Three-dimensional structure of the Golgi apparatus in mouse spermatids: a scanning electron microscopic study. (1/157)

In this study, the three-dimensional organization of the Golgi apparatus in mouse spermatids was elucidated by preparing testicular tissue with the osmium-DMSO-osmium method and examining it by stereo-scanning electron microscopy. The cis-most saccule was found to be a regular network of anastomotic membranous tubules covered by a single cisterna of ER. The trans-Golgi network was seen to be composed of irregular saccules perforated by pores at the edge. It appears that the anastomosing trans-Golgi network breaks down into strings of connected vesicles which arise from the edge of the saccules during the cap phase of spermiogenesis. Many apparently individual vesicles seen in thin sections through the trans-Golgi network are actually joined in continuous strings. This was the first time that these structures could be visualized directly without three-dimensional image reconstruction. By correlating the morphology of the Golgi apparatus with the stage of acrosome formation, the Golgi cisternae were found to change dynamically in a cis-trans direction from fenestrated saccules to continuous strings of vesicles, which finally dissipated as transport vesicles at the trans aspect. This suggests that the hypothetical model of cisternal maturation, which dictates that cargo moves through the Golgi apparatus without leaving the cisternal lumen and the secretion occurs by progressive maturation of the Golgi cisternae as they move in the cis-trans direction, may be applicable to acrosome formation.  (+info)

Ultrastructural histochemical alteration of the plasma membrane in chronic myelocytic leukemia. (2/157)

Ultrastructural histochemical evaluation of the surface of normal human blood and bone marrow cells exposed to the pyroantimonate-osmium (PAO) reaction indicated the selective binding of pyroantimonate to certain cations (calcium, magnesium, and possibly sodium) associated with the plasma membrane of neutrophilic leukocytes and their developmental forms. Other leukocytes and their precursors did not exhibit plasma membrane PAO reactivity. The extent of surface binding was related to cell maturity, with maximal labeling evident in the mid and late promyelocytes; decreased binding occurred with subsequent maturation while myeloblasts were nonreactive. This study was initiated to ascertain if histochemical surface modifications of neutrophilic cells occur in certain myeloproliferative disorders. In this regard, we have been able to demonstrate a distinctive defect in the plasma membrane PAO binding characteristics of the leukemic cells in chronic myelocytic leukemia (CML). Limited binding of pyroantimonate to the plasma membrane of the leukemic cell series in four patients with CML contrasted with that of the normal granulocytic cell series and the neutrophilic cells seen in myelomonocytic leukemia (two patients), myelofibrosis (one patient), and acute myelocytic leukemia (three patients). Comparison of surface PAO reactivity of neutrophilic cells in all stages of maturation in two patients with CML in blast crisis revealed that, in the patient with 30% circulating blast cells, PAO reactivity was identical to that noted in CML, while in the patient with 80% circulating blast forms, the PAO reactivity of the maturing neutrophilic cells more nearly resembled that observed in neutrophilic cells from normal individuals. Many neutrophilic cells from patients with myelofibrosis and myelomonocytic leukemia and from one patient in severe blast crisis had large surface deposits of pyroantimonate considered to reflect increased membrane-associated reactive cation.  (+info)

Accretion rates of meteorites and cosmic dust in the Early Ordovician. (3/157)

Abundant fossil meteorites in marine, condensed Lower Ordovician limestones from Kinnekulle, Sweden, indicate that accretion rates of meteorites were one to two orders of magnitude higher during an interval of the Early Ordovician than at present. Osmium isotope and iridium analyses of whole-rock limestone indicate a coeval enhancement of one order of magnitude in the influx rate of cosmic dust. Enhanced accretion of cosmic matter may be related to the disruption of the L chondrite parent body around 500 million years ago.  (+info)

Calcium in smooth muscle sarcoplasmic reticulum in situ. Conventional and X-ray analytical electron microscopy. (4/157)

Numerous electron-opaque deposits appear in the SR of the relaxed smooth muscle cells of the guinea pig Taenia coli that had been treated, before fixation, with a depolarizing medium containing oxalate to precipitate calcium ions in situ. X-ray spectra obtained by spot and line-scanning analyses of these deposits in situ show characteristic calcium signals, thus providing direct evidence for calcium accumulation inside the sarcoplasmic reticulum of smooth muscle.  (+info)

Electrochemical behavior of dopamine and ascorbic acid at osmium(II) complex cationic monolayer modified gold electrodes. (5/157)

The electrooxidation of dopamine (DA) and ascorbic acid (AA) was studied using gold electrodes modified by a cationic self-assembled monolayer of [Os(bpy)2(bpy-(CH2),3SH)]2+ by cyclic voltammetry. At an [Os(bpy)2(bpy-(CH2)13SH)]2+/Au electrode, the oxidation peak of DA shifted to a much more positive potential as compared with that of a bare gold electrode, while the oxidation peak potential of AA showed a slightly negative shift due to their different electrostatic interactions with the cationic monolayer. Thus, a sufficient potential difference was achieved for distinguishing the electrochemical responses of DA and AA. However, when CH3(CH2)11SH was mixed into the cationic monolayer, the enhanced packing of the mixed monolayer blocked the access of DA or AA to the electrode, resulting in further positive shifts for both oxidation-peak potentials.  (+info)

Electrochemical characterization and DNA-binding property of dipyridophenazine complexes of osmium (II). (6/157)

Novel dipyridophenazine (DPPZ) complexes of osmium (II), [Os(L)2(DPPZ)]2+ [L = 2,2'-bipyridyl (bpy)(1), 4,4'-diamino-2,2'-bipyridyl (DA-bpy)(2), 4,4'-dimethyl-2,2'-bipyridyl(DM-bpy)(3), and 4,4'-dicarboxyl-2,2'-bipyridyl (DC-bpy)(4)] have been synthesized and characterized. The DNA-binding properties of the complexes were studied by electrochemical methods. As the results, complex 2 shows higher affinity to DNA than other osmium complexes. The binding constant, K of complex 2 to calf thymus DNA has been determined to be 2.3 x 10(7) M-1 by normal pulse voltammetry (NPV).  (+info)

Buffered osmium tetroxide (OsO4) fixation for cytological and Feulgen microspectrophotometric studies of human rectal polyps. (7/157)

Evidence has been presented that when human rectal mucosa and polyps are fixed with buffered OsO(4) according to the method of Palade, staining of paraffin sections by basic and acidic dyes results in a distinct color difference between chromatin and cytoplasm. Furthermore, the Feulgen reaction also can be carried out successfully and such OsO(4)-fixed Feulgen-stained sections are especially suitable for microspectrophotometric determinations of DNA in individual nuclei.  (+info)

The use of OsO4 as fixative for Feulgen-stained preparations. (8/157)

OsO(4) has many advantages over Carnoy's fixative mixture for the Feulgen nuclear staining in the protozoan Tokophrya infusionum. While Carnoy's fluid used prior to the Feulgen reaction produces shrinkage of the macronucleus and coarse clumping of its chromatin bodies, OsO(4) preserves faithfully the size and shape of the macronucleus and its chromatin material. This finding seems to be of special importance in view of the fact that electron microscopy relies on OsO(4) fixation. The satisfactory preservation of structured detail in Feulgen-stained preparations is of importance for the correlation of histochemical and morphological information.  (+info)