Microvilli: Minute projections of cell membranes which greatly increase the surface area of the cell.Microscopy, Electron, Scanning: Microscopy in which the object is examined directly by an electron beam scanning the specimen point-by-point. The image is constructed by detecting the products of specimen interactions that are projected above the plane of the sample, such as backscattered electrons. Although SCANNING TRANSMISSION ELECTRON MICROSCOPY also scans the specimen point by point with the electron beam, the image is constructed by detecting the electrons, or their interaction products that are transmitted through the sample plane, so that is a form of TRANSMISSION ELECTRON MICROSCOPY.Microscopy, Electron: Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.Epithelium: One or more layers of EPITHELIAL CELLS, supported by the basal lamina, which covers the inner or outer surfaces of the body.Microfilament Proteins: Monomeric subunits of primarily globular ACTIN and found in the cytoplasmic matrix of almost all cells. They are often associated with microtubules and may play a role in cytoskeletal function and/or mediate movement of the cell or the organelles within the cell.Cell Membrane: The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells.Actins: Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or F-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or G-actin. In conjunction with MYOSINS, actin is responsible for the contraction and relaxation of muscle.Cytoskeleton: The network of filaments, tubules, and interconnecting filamentous bridges which give shape, structure, and organization to the cytoplasm.Microscopy, Immunoelectron: Microscopy in which the samples are first stained immunocytochemically and then examined using an electron microscope. Immunoelectron microscopy is used extensively in diagnostic virology as part of very sensitive immunoassays.Epithelial Cells: Cells that line the inner and outer surfaces of the body by forming cellular layers (EPITHELIUM) or masses. Epithelial cells lining the SKIN; the MOUTH; the NOSE; and the ANAL CANAL derive from ectoderm; those lining the RESPIRATORY SYSTEM and the DIGESTIVE SYSTEM derive from endoderm; others (CARDIOVASCULAR SYSTEM and LYMPHATIC SYSTEM) derive from mesoderm. Epithelial cells can be classified mainly by cell shape and function into squamous, glandular and transitional epithelial cells.Cytoskeletal Proteins: Major constituent of the cytoskeleton found in the cytoplasm of eukaryotic cells. They form a flexible framework for the cell, provide attachment points for organelles and formed bodies, and make communication between parts of the cell possible.Intestinal Mucosa: Lining of the INTESTINES, consisting of an inner EPITHELIUM, a middle LAMINA PROPRIA, and an outer MUSCULARIS MUCOSAE. In the SMALL INTESTINE, the mucosa is characterized by a series of folds and abundance of absorptive cells (ENTEROCYTES) with MICROVILLI.Microscopy, Electron, Transmission: Electron microscopy in which the ELECTRONS or their reaction products that pass down through the specimen are imaged below the plane of the specimen.Intestine, Small: The portion of the GASTROINTESTINAL TRACT between the PYLORUS of the STOMACH and the ILEOCECAL VALVE of the LARGE INTESTINE. It is divisible into three portions: the DUODENUM, the JEJUNUM, and the ILEUM.Phalloidine: Very toxic polypeptide isolated mainly from AMANITA phalloides (Agaricaceae) or death cup; causes fatal liver, kidney and CNS damage in mushroom poisoning; used in the study of liver damage.Kidney Tubules, Proximal: The renal tubule portion that extends from the BOWMAN CAPSULE in the KIDNEY CORTEX into the KIDNEY MEDULLA. The proximal tubule consists of a convoluted proximal segment in the cortex, and a distal straight segment descending into the medulla where it forms the U-shaped LOOP OF HENLE.Cilia: Populations of thin, motile processes found covering the surface of ciliates (CILIOPHORA) or the free surface of the cells making up ciliated EPITHELIUM. Each cilium arises from a basic granule in the superficial layer of CYTOPLASM. The movement of cilia propels ciliates through the liquid in which they live. The movement of cilia on a ciliated epithelium serves to propel a surface layer of mucus or fluid. (King & Stansfield, A Dictionary of Genetics, 4th ed)Enterocytes: Absorptive cells in the lining of the INTESTINAL MUCOSA. They are differentiated EPITHELIAL CELLS with apical MICROVILLI facing the intestinal lumen. Enterocytes are more abundant in the SMALL INTESTINE than in the LARGE INTESTINE. Their microvilli greatly increase the luminal surface area of the cell by 14- to 40 fold.Mesomycetozoea: A class of parasitic and saprophytic microorganisms whose origins can be traced near the animal-fungal divergence. Members of the class are typically pathogens of FISHES, but there are exceptions. There are two recognized orders: Icthyophonida and Dermocystida.Fluorescent Antibody Technique: Test for tissue antigen using either a direct method, by conjugation of antibody with fluorescent dye (FLUORESCENT ANTIBODY TECHNIQUE, DIRECT) or an indirect method, by formation of antigen-antibody complex which is then labeled with fluorescein-conjugated anti-immunoglobulin antibody (FLUORESCENT ANTIBODY TECHNIQUE, INDIRECT). The tissue is then examined by fluorescence microscopy.Sodium-Hydrogen Antiporter: A plasma membrane exchange glycoprotein transporter that functions in intracellular pH regulation, cell volume regulation, and cellular response to many different hormones and mitogens.Cell Polarity: Orientation of intracellular structures especially with respect to the apical and basolateral domains of the plasma membrane. Polarized cells must direct proteins from the Golgi apparatus to the appropriate domain since tight junctions prevent proteins from diffusing between the two domains.Cytochalasin D: A fungal metabolite that blocks cytoplasmic cleavage by blocking formation of contractile microfilament structures resulting in multinucleated cell formation, reversible inhibition of cell movement, and the induction of cellular extrusion. Additional reported effects include the inhibition of actin polymerization, DNA synthesis, sperm motility, glucose transport, thyroid secretion, and growth hormone release.Actin Cytoskeleton: Fibers composed of MICROFILAMENT PROTEINS, which are predominately ACTIN. They are the smallest of the cytoskeletal filaments.Cytochalasins: 11- to 14-membered macrocyclic lactones with a fused isoindolone. Members with INDOLES attached at the C10 position are called chaetoglobosins. They are produced by various fungi. Some members interact with ACTIN and inhibit CYTOKINESIS.Pigment Epithelium of Eye: The layer of pigment-containing epithelial cells in the RETINA; the CILIARY BODY; and the IRIS in the eye.Intestines: The section of the alimentary canal from the STOMACH to the ANAL CANAL. It includes the LARGE INTESTINE and SMALL INTESTINE.Freeze Etching: A replica technique in which cells are frozen to a very low temperature and cracked with a knife blade to expose the interior surfaces of the cells or cell membranes. The cracked cell surfaces are then freeze-dried to expose their constituents. The surfaces are now ready for shadowing to be viewed using an electron microscope. This method differs from freeze-fracturing in that no cryoprotectant is used and, thus, allows for the sublimation of water during the freeze-drying process to etch the surfaces.Intercellular Junctions: Direct contact of a cell with a neighboring cell. Most such junctions are too small to be resolved by light microscopy, but they can be visualized by conventional or freeze-fracture electron microscopy, both of which show that the interacting CELL MEMBRANE and often the underlying CYTOPLASM and the intervening EXTRACELLULAR SPACE are highly specialized in these regions. (From Alberts et al., Molecular Biology of the Cell, 2d ed, p792)Ependyma: A thin membrane that lines the CEREBRAL VENTRICLES and the central canal of the SPINAL CORD.Photoreceptor Cells, Invertebrate: Specialized cells in the invertebrates that detect and transduce light. They are predominantly rhabdomeric with an array of photosensitive microvilli. Illumination depolarizes invertebrate photoreceptors by stimulating Na+ influx across the plasma membrane.PhosphoproteinsOvum: A mature haploid female germ cell extruded from the OVARY at OVULATION.Cell Line: Established cell cultures that have the potential to propagate indefinitely.Digestive System: A group of organs stretching from the MOUTH to the ANUS, serving to breakdown foods, assimilate nutrients, and eliminate waste. In humans, the digestive system includes the GASTROINTESTINAL TRACT and the accessory glands (LIVER; BILIARY TRACT; PANCREAS).Jejunum: The middle portion of the SMALL INTESTINE, between DUODENUM and ILEUM. It represents about 2/5 of the remaining portion of the small intestine below duodenum.Olfactory Mucosa: That portion of the nasal mucosa containing the sensory nerve endings for SMELL, located at the dome of each NASAL CAVITY. The yellow-brownish olfactory epithelium consists of OLFACTORY RECEPTOR NEURONS; brush cells; STEM CELLS; and the associated olfactory glands.Membrane Proteins: Proteins which are found in membranes including cellular and intracellular membranes. They consist of two types, peripheral and integral proteins. They include most membrane-associated enzymes, antigenic proteins, transport proteins, and drug, hormone, and lectin receptors.Immunohistochemistry: Histochemical localization of immunoreactive substances using labeled antibodies as reagents.Choroid Plexus: A villous structure of tangled masses of BLOOD VESSELS contained within the third, lateral, and fourth ventricles of the BRAIN. It regulates part of the production and composition of CEREBROSPINAL FLUID.Sodium-Phosphate Cotransporter Proteins, Type II: A family of sodium-phosphate cotransporter proteins with eight transmembrane domains. They are present primarily in the KIDNEY and SMALL INTESTINE and are responsible for renal and small intestinal epithelial transport of phosphate.Thorium: Thorium. A radioactive element of the actinide series of metals. It has an atomic symbol Th, atomic number 90, and atomic weight 232.04. It is used as fuel in nuclear reactors to produce fissionable uranium isotopes. Because of its radioopacity, various thorium compounds are used to facilitate visualization in roentgenography.Cloaca: A dilated cavity extended caudally from the hindgut. In adult birds, reptiles, amphibians, and many fishes but few mammals, cloaca is a common chamber into which the digestive, urinary and reproductive tracts discharge their contents. In most mammals, cloaca gives rise to LARGE INTESTINE; URINARY BLADDER; and GENITALIA.Coated Pits, Cell-Membrane: Specialized regions of the cell membrane composed of pits coated with a bristle covering made of the protein CLATHRIN. These pits are the entry route for macromolecules bound by cell surface receptors. The pits are then internalized into the cytoplasm to form the COATED VESICLES.Myosin Type I: A subclass of myosins found generally associated with actin-rich membrane structures such as filopodia. Members of the myosin type I family are ubiquitously expressed in eukaryotes. The heavy chains of myosin type I lack coiled-coil forming sequences in their tails and therefore do not dimerize.Rhodnius: A genus of the subfamily TRIATOMINAE. Rhodnius prolixus is a vector for TRYPANOSOMA CRUZI.Chickens: Common name for the species Gallus gallus, the domestic fowl, in the family Phasianidae, order GALLIFORMES. It is descended from the red jungle fowl of SOUTHEAST ASIA.Histocytochemistry: Study of intracellular distribution of chemicals, reaction sites, enzymes, etc., by means of staining reactions, radioactive isotope uptake, selective metal distribution in electron microscopy, or other methods.Vomeronasal Organ: An accessory chemoreceptor organ that is separated from the main OLFACTORY MUCOSA. It is situated at the base of nasal septum close to the VOMER and NASAL BONES. It forwards chemical signals (such as PHEROMONES) to the CENTRAL NERVOUS SYSTEM, thus influencing reproductive and social behavior. In humans, most of its structures except the vomeronasal duct undergo regression after birth.Cryoultramicrotomy: The technique of using a cryostat or freezing microtome, in which the temperature is regulated to -20 degrees Celsius, to cut ultrathin frozen sections for microscopic (usually, electron microscopic) examination.Actinin: A protein factor that regulates the length of R-actin. It is chemically similar, but immunochemically distinguishable from actin.Sucrase-Isomaltase Complex: An enzyme complex found in the brush border membranes of the small intestine. It is believed to be an enzyme complex with different catalytic sites. Its absence is manifested by an inherited disease called sucrase-isomaltase deficiency.Blastomeres: Undifferentiated cells resulting from cleavage of a fertilized egg (ZYGOTE). Inside the intact ZONA PELLUCIDA, each cleavage yields two blastomeres of about half size of the parent cell. Up to the 8-cell stage, all of the blastomeres are totipotent. The 16-cell MORULA contains outer cells and inner cells.Caco-2 Cells: Human colonic ADENOCARCINOMA cells that are able to express differentiation features characteristic of mature intestinal cells, such as ENTEROCYTES. These cells are valuable in vitro tools for studies related to intestinal cell function and differentiation.Parietal Cells, Gastric: Rounded or pyramidal cells of the GASTRIC GLANDS. They secrete HYDROCHLORIC ACID and produce gastric intrinsic factor, a glycoprotein that binds VITAMIN B12.Agglutination: The clumping together of suspended material resulting from the action of AGGLUTININS.Bacterial Adhesion: Physicochemical property of fimbriated (FIMBRIAE, BACTERIAL) and non-fimbriated bacteria of attaching to cells, tissue, and nonbiological surfaces. It is a factor in bacterial colonization and pathogenicity.Swine: Any of various animals that constitute the family Suidae and comprise stout-bodied, short-legged omnivorous mammals with thick skin, usually covered with coarse bristles, a rather long mobile snout, and small tail. Included are the genera Babyrousa, Phacochoerus (wart hogs), and Sus, the latter containing the domestic pig (see SUS SCROFA).Cells, Cultured: Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.Triatominae: A subfamily of assassin bugs (REDUVIIDAE) that are obligate blood-suckers of vertebrates. Included are the genera TRIATOMA; RHODNIUS; and PANSTRONGYLUS, which are vectors of TRYPANOSOMA CRUZI, the agent of CHAGAS DISEASE in humans.Rabbits: The species Oryctolagus cuniculus, in the family Leporidae, order LAGOMORPHA. Rabbits are born in burrows, furless, and with eyes and ears closed. In contrast with HARES, rabbits have 22 chromosome pairs.Cell Adhesion: Adherence of cells to surfaces or to other cells.Microscopy, Fluorescence: Microscopy of specimens stained with fluorescent dye (usually fluorescein isothiocyanate) or of naturally fluorescent materials, which emit light when exposed to ultraviolet or blue light. Immunofluorescence microscopy utilizes antibodies that are labeled with fluorescent dye.Freeze Fracturing: Preparation for electron microscopy of minute replicas of exposed surfaces of the cell which have been ruptured in the frozen state. The specimen is frozen, then cleaved under high vacuum at the same temperature. The exposed surface is shadowed with carbon and platinum and coated with carbon to obtain a carbon replica.Cytoplasm: The part of a cell that contains the CYTOSOL and small structures excluding the CELL NUCLEUS; MITOCHONDRIA; and large VACUOLES. (Glick, Glossary of Biochemistry and Molecular Biology, 1990)LLC-PK1 Cells: Epithelial cell line originally derived from porcine kidneys. It is used for pharmacologic and metabolic studies.Glycocalyx: The carbohydrate-rich zone on the cell surface. This zone can be visualized by a variety of stains as well as by its affinity for lectins. Although most of the carbohydrate is attached to intrinsic plasma membrane molecules, the glycocalyx usually also contains both glycoproteins and proteoglycans that have been secreted into the extracellular space and then adsorbed onto the cell surface. (Alberts et al., Molecular Biology of the Cell, 3d ed, p502)Leukocyte Rolling: Movement of tethered, spherical LEUKOCYTES along the endothelial surface of the microvasculature. The tethering and rolling involves interaction with SELECTINS and other adhesion molecules in both the ENDOTHELIUM and leukocyte. The rolling leukocyte then becomes activated by CHEMOKINES, flattens out, and firmly adheres to the endothelial surface in preparation for transmigration through the interendothelial cell junction. (From Abbas, Cellular and Molecular Immunology, 3rd ed)Vitelline Membrane: The plasma membrane of the egg.Microscopy, Confocal: A light microscopic technique in which only a small spot is illuminated and observed at a time. An image is constructed through point-by-point scanning of the field in this manner. Light sources may be conventional or laser, and fluorescence or transmitted observations are possible.Ranvier's Nodes: Regularly spaced gaps in the myelin sheaths of peripheral axons. Ranvier's nodes allow saltatory conduction, that is, jumping of impulses from node to node, which is faster and more energetically favorable than continuous conduction.Heymann Nephritis Antigenic Complex: A complex of antigenic proteins obtained from the brush border of kidney tubules. It contains two principal components LOW DENSITY LIPOPROTEIN RECEPTOR-RELATED PROTEIN-2 and LDL-RECEPTOR RELATED PROTEIN-ASSOCIATED PROTEIN. The name of this complex is derived from researcher, Dr. Walter Heymann, who developed an experimental model of membranous glomerulonephritis (GLOMERULONEPHRITIS) by injecting this antigenic complex into rats to induce an autoimmune response.Myosins: A diverse superfamily of proteins that function as translocating proteins. They share the common characteristics of being able to bind ACTINS and hydrolyze MgATP. Myosins generally consist of heavy chains which are involved in locomotion, and light chains which are involved in regulation. Within the structure of myosin heavy chain are three domains: the head, the neck and the tail. The head region of the heavy chain contains the actin binding domain and MgATPase domain which provides energy for locomotion. The neck region is involved in binding the light-chains. The tail region provides the anchoring point that maintains the position of the heavy chain. The superfamily of myosins is organized into structural classes based upon the type and arrangement of the subunits they contain.Microscopy, Phase-Contrast: A form of interference microscopy in which variations of the refracting index in the object are converted into variations of intensity in the image. This is achieved by the action of a phase plate.Organoids: An organization of cells into an organ-like structure. Organoids can be generated in culture. They are also found in certain neoplasms.SucraseTime Factors: Elements of limited time intervals, contributing to particular results or situations.Photoreceptor Cells: Specialized cells that detect and transduce light. They are classified into two types based on their light reception structure, the ciliary photoreceptors and the rhabdomeric photoreceptors with MICROVILLI. Ciliary photoreceptor cells use OPSINS that activate a PHOSPHODIESTERASE phosphodiesterase cascade. Rhabdomeric photoreceptor cells use opsins that activate a PHOSPHOLIPASE C cascade.Membrane Glycoproteins: Glycoproteins found on the membrane or surface of cells.Carrier Proteins: Transport proteins that carry specific substances in the blood or across cell membranes.Placenta: A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (CHORIONIC VILLI) derived from TROPHOBLASTS and a maternal portion (DECIDUA) derived from the uterine ENDOMETRIUM. The placenta produces an array of steroid, protein and peptide hormones (PLACENTAL HORMONES).Malpighian Tubules: Slender tubular or hairlike excretory structures found in insects. They emerge from the alimentary canal between the mesenteron (midgut) and the proctodeum (hindgut).Octoxynol: Nonionic surfactant mixtures varying in the number of repeating ethoxy (oxy-1,2-ethanediyl) groups. They are used as detergents, emulsifiers, wetting agents, defoaming agents, etc. Octoxynol-9, the compound with 9 repeating ethoxy groups, is a spermatocide.Models, Biological: Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.Opossums: New World marsupials of the family Didelphidae. Opossums are omnivorous, largely nocturnal and arboreal MAMMALS, grow to about three feet in length, including the scaly prehensile tail, and have an abdominal pouch in which the young are carried at birth.DisaccharidasesCytochalasin B: A cytotoxic member of the CYTOCHALASINS.Pinocytosis: The engulfing of liquids by cells by a process of invagination and closure of the cell membrane to form fluid-filled vacuoles.Apocrine Glands: Large, branched, specialized sweat glands that empty into the upper portion of a HAIR FOLLICLE instead of directly onto the SKIN.Hair Cells, Auditory: Sensory cells in the organ of Corti, characterized by their apical stereocilia (hair-like projections). The inner and outer hair cells, as defined by their proximity to the core of spongy bone (the modiolus), change morphologically along the COCHLEA. Towards the cochlear apex, the length of hair cell bodies and their apical STEREOCILIA increase, allowing differential responses to various frequencies of sound.Cytoplasmic Granules: Condensed areas of cellular material that may be bounded by a membrane.Destrin: A member of the actin depolymerizing factors. Its depolymerizing activity is independent of HYDROGEN-ION CONCENTRATION.Sodium-Phosphate Cotransporter Proteins, Type IIa: An electrogenic sodium-dependent phosphate transporter. It is present primarily in BRUSH BORDER membranes of PROXIMAL RENAL TUBULES.Myosin Heavy Chains: The larger subunits of MYOSINS. The heavy chains have a molecular weight of about 230 kDa and each heavy chain is usually associated with a dissimilar pair of MYOSIN LIGHT CHAINS. The heavy chains possess actin-binding and ATPase activity.

Neural modulation of cephalexin intestinal absorption through the di- and tripeptide brush border transporter of rat jejunum in vivo. (1/2805)

Intestinal absorption of beta-lactamine antibiotics (e.g., cefixime and cephalexin) has been shown to proceed through the dipeptide carrier system. In a previous study, nifedipine (NFP), an L-type calcium channel blocker, enhanced the absorption of cefixime in vivo but not in vitro, and it was suggested that neural mechanisms might be involved in the effect of NFP. The aim of the present study was to assess the involvement of the nervous system on the intestinal absorption of cephalexin (CFX). To investigate this, we used a single-pass jejunal perfusion technique in rats. NFP and diltiazem enhanced approximately 2-fold the plasma levels of CFX in treated rats versus untreated controls. NFP also increased approximately 2-fold the CFX level in portal plasma and increased urinary excretion of CFX, thus indicating that CFX did effectively increase CFX intestinal absorption. Perfusing high concentrations of dipeptides in the jejunal lumen competitively reduced CFX absorption and inhibited the enhancement of CFX absorption produced by NFP. Hexamethonium and lidocaine inhibited the effect of NFP, whereas atropine, capsaicin, clonidine, and isoproterenol enhanced CFX absorption by the same order of magnitude as NFP. Thus, complex neural networks can modulate the function of the intestinal di- and tripeptide transporter. Sympathetic noradrenergic fibers, intestinal sensory neurons, and nicotinic synapses are involved in the increase of CFX absorption produced by NFP.  (+info)

Evidence for an anion exchange mechanism for uptake of conjugated bile acid from the rat jejunum. (2/2805)

Absorption of conjugated bile acids from the small intestine is very efficient. The mechanisms of jejunal absorption are not very well understood. The aim of this study was to clarify the mechanism of absorption of conjugated bile acid at the apical membrane of jejunal epithelial cells. Brush-border membrane vesicles from intestinal epithelial cells of the rat were prepared. Absorption of two taurine-conjugated bile acids that are representative of endogenous bile acids in many variate vertebrate species were studied. In ileal, but not jejunal brush-border membrane vesicles, transport of conjugated bile acids was cis-stimulated by sodium. Transport of conjugated bile acids was trans-stimulated by bicarbonate in the jejunum. Absorption of conjugated dihydroxy-bile acids was almost twice as fast as of trihydroxy-bile acids. Coincubation with other conjugated bile acids, bromosulfophthalein, and DIDS, as well as by incubation in the cold inhibited the transport rate effectively. Absorption of conjugated bile acids in the jejunum from the rat is driven by anion exchange and is most likely an antiport transport.  (+info)

Immunohistochemical localization of multispecific renal organic anion transporter 1 in rat kidney. (3/2805)

Renal proximal convoluted tubules have an important role, i.e., to excrete organic anions, including numerous drugs and endogenous substances. Recently, multispecific organic anion transporter 1 (OAT1) was isolated from rat kidney. In this study, the cellular and subcellular localization of OAT1 in rat kidney was investigated. Kidneys from normal rats were perfused and fixed with periodate-lysine-paraformaldehyde solution and were then processed for immunohistochemical analysis using the labeled streptavidin-biotin method, preembedding horseradish peroxidase method, and immunogold method. Light microscopic examination revealed immunostaining for OAT1 in the middle portion of the proximal tubule (S2 segment), but not in the initial portion of the proximal convoluted tubule, next to the glomerulus. Nephron segments other than the S2 segment and the renal vasculature were not stained with antibody to OAT1. Electron-microscopic observation using a preembedding method revealed that OAT1 was exclusively expressed in the basolateral membrane of S2 segments of proximal tubules. The immunogold method showed no labeling for OAT1 in the cytoplasmic vesicles, suggesting that OAT1 may not move together with organic anions into the cells. These results are consistent with previous physiologic data showing that organic anions, including para-aminohippurate, are taken up by the basolateral Na+-independent organic anion/dicarboxylate exchanger and excreted at S2 segments. In conclusion, OAT1 was localized to the basolateral membrane of S2 segments of proximal tubules in rat kidneys.  (+info)

Calcium does not inhibit iron absorption or alter iron status in infant piglets adapted to a high calcium diet. (4/2805)

The purpose of this study was to investigate whether a dietary calcium:iron ratio similar to that often consumed by premature human infants inhibits iron absorption in infant piglets adapted to a high calcium diet. Male Yorkshire piglets were randomized at 3 to 4 d of age to a high calcium diet (4.67 g/L = HC) or a normal calcium diet (2.0 g/L = NC) and fed for 2 to 2.5 wk. An iron dextran injection was administered in amounts to achieve a marginal state of iron repletion to simulate iron status of premature infants. In vivo iron absorption from the diet was determined using the radiotracers 55Fe and 59Fe and whole body counting. Calcium:iron interactions at absorption sites in piglets fed HC and NC were investigated by measurements of time-dependent 59Fe uptake in response to different calcium:iron ratios in vitro in brush border membrane vesicles (BBMV). In vivo iron absorption from the diet did not differ between NC and HC diet groups [57 +/- 8% versus 55 +/- 17% (mean +/- SD), respectively]. Iron status and iron contencentrations in spleen, liver, intestine, kidney and heart did not differ between diet groups. Iron uptake in BBMV was significantly reduced by calcium in both HC and NC (P < 0.001); but there were no significant differences in iron uptake in response to different calcium:iron ratios between HC and NC. With feeding a HC diet for 2 wk there may be an adaptive response to counteract the inhibitory effects of calcium on iron absorption, thus resulting in similar in vivo iron absorption and iron status irrespective of the 1.3-fold difference in dietary calcium:iron ratio between piglet groups. However, future studies are needed to determine the specific sites of calcium:iron interactions and adaptation mechanisms. Since the calcium:iron ratios used in this study reflect the usual calcium:iron ratios in diets for premature infants, it is unlikely that interactive effects of calcium with iron will compromise iron status in this infant population when diets are supplemented with calcium.  (+info)

Multiplicity of the H+-dependent transport mechanism of dipeptide and anionic beta-lactam antibiotic ceftibuten in rat intestinal brush-border membrane. (5/2805)

To elucidate the transport characteristics of the H+/dipeptide carrier that recognizes the orally active beta-lactam antibiotic ceftibuten, the uptake behaviors were compared of ceftibuten and Gly-Sar by rat intestinal brush-border membrane vesicles. The results show that 1) both the uptake of ceftibuten and that of Gly-Sar were dependent on an inwardly directed H+ gradient; 2) anionic compounds such as hippurylphenyllactic acid competitively inhibited ceftibuten uptake in the presence of H+ gradient, whereas this anion did not inhibit Gly-Sar uptake; and 3) the carrier-mediated uptake of ceftibuten did not disappear even in the presence of 20 mM Gly-Sar. The results provide an evidence that several transporters with different features are potentially responsible for the uptake of beta-lactam antibiotics into the intestinal cells. It is suggested that the dianionic beta-lactam antibiotics that carry a net negative charge such as ceftibuten use multiple H+-dependent transport systems for absorption.  (+info)

Cimetidine transport in brush-border membrane vesicles from rat small intestine. (6/2805)

In previous studies, sulfoxide metabolite was observed in animal and human intestinal perfusions of cimetidine and other H2-antagonists. A sequence of follow-up studies is ongoing to assess the intestinal contributions of drug metabolism and drug and metabolite transport to variable drug absorption. An evaluation of these contributions to absorption variability is carried out in isolated fractions of the absorptive cells to uncouple the processes involved. In this report, data is presented on the drug entry step from a study on [3H]cimetidine uptake into isolated brush-border membrane vesicles from rat small intestine. A saturable component for cimetidine uptake was characterized with a Vmax and Km (mean +/- S.E.M.) of 6.1 +/- 1.5 nmol/30s/mg protein and 8.4 +/- 2.0 mM, respectively. Initial binding, and possibly intravesicular uptake, was inhibited by other cationic compounds including ranitidine, procainamide, imipramine, erythromycin, and cysteamine but not by TEA or by the organic anion, probenecid. Initial uptake was not inhibited by amino acids methionine, cysteine, or histidine, by the metabolite cimetidine sulfoxide, or by inhibitors of cimetidine sulfoxidation, methimazole, and diisothiocyanostilbene-2,2'-disulfonic acid. Equilibrium uptake was inhibited by ranitidine, procainamide, and cysteamine but not by erythromycin or imipramine. Initial cimetidine uptake was stimulated by an outwardly directed H+ gradient, and efflux was enhanced by an inwardly directed H+ gradient. Collapse of the H+ gradient as well as voltage-clamping potential difference to zero significantly reduced initial cimetidine uptake. The data is supportive of both a cimetidine/H+ exchange mechanism and a driving-force contribution from an inside negative proton or cation diffusion potential.  (+info)

Cyclical changes in epithelial cells of the vaginal cul-de-sac of brushtail possums (Trichosurus vulpecula). (7/2805)

The aim of this study was to describe and quantify the changes that occur in cul-de-sac tissue, in particular to epithelial cells and their constituents, at specific stages of the estrous cycle in the brushtail possum. Stereological techniques were used to quantify changes in cul-de-sac epithelial cells collected at four stages of the estrous cycle; the time of removal of pouch young (RPY; n = 5), of initial follicle development (n = 5), of preovulatory follicle formation (n = 5), of midluteal stage (n = 4), and again at RPY (n = 5) after completion of the experiment to examine for any effects due to season or time. Tissue was weighed and processed for light microscopy, transmission electron microscopy, and stereological analysis. Cul-de-sac epithelial cell volume increased approximately 17-fold at the time of preovulatory follicle formation compared with that at the time of RPY, before declining (approximately four-fold greater than at RPY) during the midluteal phase. Epithelial cell volume enlargement was correlated strongly with the size of the preovulatory follicle present, and maximum size was coincidental with the formation of extracellular spaces and projection of cell processes between lateral cell membranes. Maximum cell volume was associated with an approximate 25-fold and six-fold increase in cytoplasmic and nuclear volume, respectively. Enlargement of the epithelial cells coincided with an increase in cytoplasmic organelle numbers, microvilli prominence, and accumulation of secretory vesicles. In the possum, the cul-de-sac epithelial cell undergoes phenomenal remodelling during the estrous cycle to accommodate an approximate 17-fold increase in volume. This increase in cell volume is coincident with morphological changes characteristic of secretory activity and appears to be under estrogen regulation.  (+info)

The meningococcal PilT protein is required for induction of intimate attachment to epithelial cells following pilus-mediated adhesion. (8/2805)

The ability of Neisseria meningitidis (MC) to interact with cellular barriers is essential to its pathogenesis. With epithelial cells, this process has been modeled in two steps. The initial stage of localized adherence is mediated by bacterial pili. After this phase, MC disperse and lose piliation, thus leading to a diffuse adherence. At this stage, microvilli have disappeared, and MC interact intimately with cells and are, in places, located on pedestals of actin, thus realizing attaching and effacing (AE) lesions. The bacterial attributes responsible for these latter phenotypes remain unidentified. Considering that bacteria are nonpiliated at this stage, pili cannot be directly responsible for this effect. However, the initial phase of pilus-mediated localized adherence is required for the occurrence of diffuse adherence, loss of microvilli, and intimate attachment, because nonpiliated bacteria are not capable of such a cellular interaction. In this work, we engineered a mutation in the cytoplasmic nucleotide-binding protein PilT and showed that this mutation increased piliation and abolished the dispersal phase of bacterial clumps as well as the loss of piliation. Furthermore, no intimate attachment nor AE lesions were observed. On the other hand, PilT- MC remained adherent as piliated clumps at all times. Taken together these data demonstrate that the induction of diffuse adherence, intimate attachment, and AE lesions after pilus-mediated adhesion requires the cytoplasmic PilT protein.  (+info)

  • Seeking to depict microvilli in a new light, Betty set out to handcraft a large-scale collage of an intestinal brush border using cutouts from discarded vintage travel books. (artlabvanderbilt.com)
  • Several drugs, including epidermal growth factor, octreotide, glutamine, and chlorpromazine, have been tried to counteract the massive secretory diarrhea in patients with microvillus atrophy. (medscape.com)
  • She also created several logos for the Tyska Lab, all of which incorporate microvilli that were previously imaged by members of the lab. (artlabvanderbilt.com)
  • The web of microfilaments is from the bundles of apical filaments at the core of a microvillus as well as from adherens junctions in myosin and in other proteins characteristic of an actomyosin motor system. (biology-online.org)
  • Though these are cellular extensions, there are little or no cellular organelles present in the microvilli. (wikipedia.org)
  • For example, enzymes that digest carbohydrates called glycosidases are present at high concentrations on the surface of enterocyte microvilli. (wikipedia.org)
  • Their name derives from the characteristic morphology of their apical or lumen-facing surface which has few if any microvilli. (iphone-cheats.com)