Hydrostatic pressure modifies the action of octanol and atropine on frog endplate conductance. (73/84)

The effects of octanol, ethanol and atropine were examined on the time course of decay (tau D) of miniature endplate currents (m.e.p.cs) in the frog neuromuscular junction at normal and high pressure. Octanol (25-100 microM) decreased reversibly the tau D of m.e.p.cs in a dose-dependent manner, 100 microM reducing tau D to 0.39 of the control value. Higher concentrations (200-500 microM) additionally depressed the amplitude of m.e.p.cs. Hydrostatic pressure (3.19 and 5.25 MPa) reduced the tau D of octanol (25-100 microM)-shortened m.e.p.cs. Thus 3.19 MPa and 5.25 MPa reduced the tau D in the presence of 100 microM octanol to 0.75 and 0.78 of the octanol treated values. This effect was not completely reversed on decompression. The m.e.p.c. amplitude is reversibly decreased by pressure in the presence of octanol. Hydrostatic pressure (3.19-15.55 MPa) did not modify the effect of ethanol on tau D. At 10.40 and 15.55 MPa the tau D was increased equally in the absence or presence of ethanol. Atropine (60 microM) reduced the tau D and amplitude of m.e.p.cs to 0.33 and 0.63 of the control values. These effects were completely reversible. Hydrostatic pressure (3.19 and 5.25 MPa) reduced the tau D of atropine-shortened m.e.p.cs to 0.82 and 0.77 of the atropine-treated values respectively. This effect was not completely reversed on decompression. Hydrostatic pressure also reversibly depressed the amplitude of atropine-treated m.e.p.cs. The implications of these drug-hydrostatic pressure interactions are discussed.  (+info)

Pressure reversal of the action of octanol on postsynaptic membranes from Torpedo. (74/84)

Octanol increases the binding of [3H]-acetylcholine to the desensitized state of the nicotinic receptor in postsynaptic membranes prepared from Torpedo californica. This increase in binding results from an increase in the affinity of [3H]-acetylcholine for its receptor without any change in the number of sites or the shape of the acetylcholine binding curve. High pressures of helium (300 atm) decrease [3H]-acetylcholine binding by a mechanism that changes only the affinity of acetylcholine binding. Helium pressure reverses the effect of octanol on the affinity of [3H]-acetylcholine for its receptor. This pressure reversal of the action of octanol at a postsynaptic membrane is consistent either with pressure counteracting an octanol-induced membrane expansion or with independent mechanisms for the actions of octanol and pressure. The data do not conform with a mechanism in which pressure displaces octanol from a binding site on the receptor protein.  (+info)

Divergent seven transmembrane receptors are candidate chemosensory receptors in C. elegans. (75/84)

Using their senses of taste and smell, animals recognize a wide variety of chemicals. The nematode C. elegans has only fourteen types of chemosensory neurons, but it responds to dozens of chemicals, because each chemosensory neuron detects several stimuli. Here we describe over 40 highly divergent members of the G protein-coupled receptor family that could contribute to this functional diversity. Most of these candidate receptor genes are in clusters of two to nine similar genes. Eleven of fourteen tested genes appear to be expressed in small subsets of chemosensory neurons. A single type of chemosensory neuron can potentially express at least four different receptor genes. Some of these genes might encode receptors for water-soluble attractants, repellents, and pheromones.  (+info)

Growth on octane alters the membrane lipid fatty acids of Pseudomonas oleovorans due to the induction of alkB and synthesis of octanol. (76/84)

Growth of Pseudomonas oleovorans GPo1, which contains the OCT plasmid, on octane results in changes in the membrane phospholipid fatty acid composition. These changes were not found for GPo12, an OCT-plasmid-cured variant of GPo1, during growth in the presence or absence of octane, implying the involvement of OCT-plasmid-encoded functions. When recombinant strain GPo12(pGEc47) carrying the alk genes from the OCT plasmid was grown on octane, the cells showed the same changes in fatty acid composition as those found for GPo1, indicating that such changes result from induction and expression of the alk genes. This finding was corroborated by inducing GPo12(pGEc47) with dicyclopropylketone (DCPK), a gratuitous inducer of the alk genes. Further experiments showed that the increase of the mean acyl chain length of fatty acids is related to the expression of alkB, which encodes a major integral membrane protein, while the formation of trans unsaturated fatty acids mainly results from the effects of 1-octanol, an octane oxidation product.  (+info)

Cell-to-cell communication in a differentiating ovine lens culture system. (77/84)

PURPOSE: This study was performed to determine whether the junctions between both the epithelial and the differentiating fiber-like cells of ovine lens cultures, like gap junctions in other tissues, exhibit cell-to-cell communication that is inhibited by n-octanol, and to determine whether lens connexins and the fiber cell membrane proteins MP20 and MP26 are expressed by these ovine lens cell cultures. METHODS: Cells were injected with Lucifer yellow CH to measure cell-to-cell communication. Antibodies to connexin-related lens membrane protein MP70, connexin 43 (Cx43), and connexin 46 (Cx46) and to membrane proteins MP20 and MP26 were used to immunofluorescently label lens cultures and probe Western blots of membranes isolated from lens cultures. RESULTS: Both epithelial cells and differentiating clear cells exhibited cell-to-cell transfer of Lucifer yellow that was inhibited by n-octanol. Although a Cx43 antibody immunofluorescently labeled small plaques between the epithelial cells, an MP70 antibody labeled large plaques as well as small punctate areas of the differentiating fiber-like cells. It is interesting that Cx43 and MP70 were frequently present in the same plaques at cell interfaces between epithelial cells as well as some of the larger plaques on the differentiating fiber-like cells. Cx46 and MP70 antibodies labeled the same plaques in membranes of differentiating fiber-like cells and late-stage epithelial cells. The electrophoretic mobility of all three connexin proteins was modified after treatment with alkaline phosphatase. Immunohistochemical staining of these differentiating regions and Western immunoblotting of purified membranes derived from differentiated cultures also showed the presence of MP20 and MP26. CONCLUSIONS: The different cell types in the ovine lens culture exhibit gap junction-mediated cell-to-cell communication that is likely effected by one or more of the connexin proteins.  (+info)

Functional role of follicular cells in the generation of osmolarity-dependent Cl- currents in Xenopus follicles. (78/84)

1. Osmolarity-dependent (osmo-dependent) ionic currents from follicle-enclosed Xenopus oocytes (follicles) were studied using the two-microelectrode voltage-clamp technique, combined with intra-oocyte pressure injection of sucrose or polyethylene glycols (PEGs). 2. Intra-oocyte injections of sucrose or PEG (3-25 nmol) generated inward membrane currents (follicles held at -60 mV) associated with an increase in membrane conductance. These currents were carried mainly by chloride ions (ICl(osm)), and were strongly attenuated by increasing the tonicity of the external medium, or by external application of La3+ (0.1-1 mM). 3. The ability to generate ICl(osm) depended on the molecular weight of the injected PEG. Injections of PEG 200 or 300 generated ICl(osm) in 95% of the follicles tested, PEG 600 generated comparable currents in only 20% of the follicles, while similar injections of PEG 1000 did not elicit ICl(osm). 4. Octanol (1-1.5 mM), a gap junction channel blocker, reversibly inhibited 50-90% of the ICl(osm) generated by injections of sucrose or PEG 300. Moreover, sucrose or PEG injections did not elicit ICl(osm) in defolliculated oocytes. 5. It is concluded that an increase in the internal osmolarity of the follicular cells activates a mechanism, probably involving cellular swelling, which leads to the opening of ICl(osm) channels most probably located in the follicular cell membrane.  (+info)

Are there functional gap junctions or junctional hemichannels in macrophages? (79/84)

The existence of functional gap junctions in migratory cells of the immune system is a controversial issue. In this report, we have focused on one particular cell type, namely the macrophages, because connexin-43, a protein that forms gap junctions, has been described in peritoneal macrophages and a macrophage cell line (J774), by Northern and Western blot analysis. To test whether these cell types expressed functional gap junctions, we assayed dye coupling by intracellular injection of Lucifer Yellow. We observed that nonstimulated macrophages are not coupled among themselves and did not form functional gap junctions with an epithelial cell line, which expresses functional gap junctions formed by connexin-43. Dye coupling was also not detected between macrophages previously activated by lipopolysaccharide or interferon-gamma. We further examined the presence of functional coupling using the more sensitive technique of dual whole cell patch-clamp, and again, did not find electrical coupling between macrophages, consistent with the dye microinjection data. We also examined the possible presence of hemigap junction channels activated by extracellular adenosine triphosphate (ATP) using a dye uptake assay and the whole cell patch-clamp technique. Conditions expected to close gap junction hemichannels (exposure to octanol and low intracellular pH) did not decrease ATP-induced Lucifer Yellow uptake, whereas conditions expected to increase hemichannel opening either did not affect ATP permeabilization (dibutyryl adenosine monophosphate) or decreased it (zero extracellular CA+2). Finally, in experiments using resident macrophages derived from conexin-43 knockout mice, we observed ATP induced dye uptake. Our experimental data thus indicate that macrophages in vitro do not form functional gap junctions and that the permeability pathway activated by extracellular ATP is not formed by a hemigap junction channel.  (+info)

Involvement of pre- and postsynaptic mechanisms in posttetanic potentiation at Aplysia synapses. (80/84)

Posttetanic potentiation (PTP) is a common form of short-term synaptic plasticity that is generally thought to be entirely presynaptic. Consistent with that idea, PTP of evoked excitatory postsynaptic potentials at Aplysia sensory-motor neuron synapses in cell culture was reduced by presynaptic injection of a slow calcium chelator and was accompanied by an increase in the frequency but not the amplitude of spontaneous excitatory postsynaptic potentials. However, PTP was also reduced by postsynaptic injection of a rapid calcium chelator or postsynaptic hyperpolarization. Thus, PTP at these synapses is likely to involve a postsynaptic induction mechanism in addition to the known presynaptic mechanisms.  (+info)