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W Shain

Publications and source records attributed to W Shain.

At least 55 records · Page 3Linked to original sources
PubMed1986

Activation of beta-adrenergic receptors stimulates release of an inhibitory transmitter from astrocytes.

Activation of beta-adrenergic receptors on astrocytes in primary cell culture results in the release of taurine, an inhibitory transmitter. Taurine release occurs via a cyclic AMP-mediated intracellular pathway, because (a) taurine release and intracellular cyclic AMP accumulation have similar pharmacologies and time courses of activation and (b) N6,O2'-dibutyryl cyclic AMP stimulates release with a time course similar to that observed with the beta-adrenergic agonist isoproterenol. These results describe a previously unrecognized physiological function of astrocytes in the CNS-receptor-mediated release of the neuroactive amino acid taurine. This observation indicates that astrocytes may function as local regulators of neuronal activity.

Alprenolol↗
PubMed1986

Identification and characterization of substance P receptors on LRM55 glial cells.

Substance P (SP) receptors were described by the specific binding of [3H]SP to several neuronal and glial cell lines. The neuronal cell lines N18 and NG108-15 were found to contain few if any SP receptors (less than 5 fmol/mg of protein). The glial cell line LRM55 contained large numbers (Bmax = 707 fmol/mg of protein) of a single class of SP binding sites (Kd = 276 pM). [3H]SP binding could be inhibited by a number of c-terminal SP fragments and the tachykinins physalaemin, eledoisin and kassinin. The binding kinetics and pharmacology of these receptors are similar to those the authors have previously described in the brain. Activation of SP receptors was shown to inhibit cyclic AMP-dependent, beta adrenergic-stimulated taurine release from LRM55 glial cells. SP inhibition must occur by mechanisms affecting taurine release after adenylate cyclase activation, inasmuch as SP has no significant effect on beta adrenergic-stimulated increases or basal levels of intracellular cyclic AMP.

Animals↗
PubMed1985

Aryl hydrocarbon hydroxylase induction in adult rat hepatocytes in primary culture by several chlorinated aromatic hydrocarbons including 2,3,7,8-tetrachlorodibenzo-p-dioxin.

The induction of aryl hydrocarbon hydroxylase (AHH) by Aroclor 1254, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other polychlorinated organic compounds was examined in primary cultures of adult rat hepatocytes isolated by a collagenase perfusion technique. Following exposure of fresh hepatocyte cultures to 1 microgram/ml Aroclor 1254, AHH induction was undetected for 48 hr and then increased dramatically up to 96 hr. Cultures maintained in control medium for either 24, 48, or 72 hr prior to a 24-hr exposure to Aroclor 1254 displayed significant inducible AHH which was sustained to 96 hr. AHH induction was extremely sensitive to two planar polyaromatic hydrocarbons, 2,3,7,8-TCDD and 2,3,7,8-tetrachlorodibenzofuran, and the PCB congener 3,4,3',4'-tetrachlorobiphenyl, but insensitive to 2,6-dichlorodibenzofuran, 2,5,2',5'-tetrachlorobiphenyl, 2,4,5,2',4',5'-hexachlorobiphenyl, and hexachlorobenzene. The induction of AHH activity in primary cultures of adult rat hepatocytes may represent a useful bioassay for screening extracts of foodstuffs, biological fluids, or environmental samples for dioxin-like activity.

Animals↗
PubMed1985

Beta-receptor-stimulated and cyclic adenosine 3',5'-monophosphate-mediated taurine release from LRM55 glial cells.

Adrenergic stimulation of LRM55 glial cells results in the release of the neuroactive amino acid taurine. The present study characterizes the receptors involved in taurine release and shows that taurine release is mediated by cyclic adenosine 3',5'-monophosphate (cAMP). beta-Receptors in LRM55 cells were first characterized by [125I]iodohydroxybenzylpindolol binding. Binding was stereospecific and saturable with time and ligand concentration. Kinetic analysis of equilibrium binding at 37 degrees C revealed a single component of high affinity (Km = 113 pm; Bmax = 52.1 +/- 5.0 fmol/mg of protein). The pharmacologies of the stimulation of cAMP accumulation and taurine release were similar. The agonists isoproterenol (IPR), epinephrine (E) and norepinephrine (NE) showed a rank order of potency characteristic of a beta-adrenergic system (IPR greater than E greater than or equal to NE). The beta-antagonists alprenolol and propranolol inhibited the IPR stimulation of both processes; the alpha-antagonist phentolamine did not. The dependence of taurine release on cAMP was further suggested by the similarity of the two time courses and was demonstrated by the stimulation of taurine release by the cAMP analogue dibutyryl cAMP. Thus, one physiological response of glial cells to beta-adrenergic stimulation is the release of taurine. Receptor-activated release of taurine from glia represents a previously undescribed neuronal-glial interaction by which glia may actively regulate neuronal excitability.

Animals↗
PubMed1980

Chemosensitivity of single smooth muscle cells to acetylcholine, noradrenaline, and histamine in vitro.

Electrical responses to acetylcholine, noradrenaline, and histamine were recorded from solitary smooth muscle cells. Iontophoresis of each transmitter elicited three fast responses: a hyperpolarization, a depolarization, or a biphasic hyperpolarization-depolarization. Each transmitter activated a specific receptor since responses were specifically blocked by antagonists, two transmitters elicited different responses in solitary cells, and desensitization of response to one transmitter did not cause desensitization of responses to other transmitters. Responses were due to increased ion conductances since input resistance decreased during responses and reversal potentials were measured for depolarizing responses (-5 mV) and hyperpolarizing responses (-60 mV). Regional differences in transmitter sensitivity were mapped on solitary cells. Biphasic responses were due to simultaneous activation of receptors mediating hyperpolarizing responses and receptors mediating depolarizing responses which were segregated in the cell membrane. Noradrenaline enhanced action potential amplitude by regulation of voltage-dependent ion conductances. Finally, noradrenaline and histamine elicited periodic hyperpolarizing potentials, which may be due to increased intracellular Ca++.

Acetylcholine↗
PubMed1980

Interaction of chemotactic factors with human polymorphonuclear leukocytes: studies using a membrane potential-sensitive cyanine dye.

Changes in the fluorescence intensity of the dye 3-3' dipentyloxacarbocyanine were measured in suspensions of purified human peripheral blood polymorphonuclear leukocytes (PMNs) during exposure to the chemotactic factors N-formyl-methionyl-leucyl-phenylalanine (f-met-leu-phe) and partially purified C5a. Incubation of PMNs with dye resulted in a stable fluorescence reflecting the resting membrane potential of the cell. Exposure of PMNs to dye did not affect stimulated chemotaxis or secretion. The mechanism of cell-associated dye fluorescence involved solvent effects from partitioning of the eye between the aqueous incubation medium and the cell and not dye aggregation, Chemotactically active concentrations of f-met-leu-phe (5 x 10(-9) M or greater) produced a biphasic response characterized as a decrease followed by an increase in fluorescence. No fluorescence response was seen in lysed PMNs, and no response was elicited by an inhibitor of f-met-leu-phe binding (carbobenzoxy-phenylalanyl-methionine). The ability of several other synthetic peptides to elicit a fluorescence response corresponded to their effectiveness as chemotactic agents. Although the first component of the response suggested a depolarization, it was not influenced by variation in the external concentration of sodium, potassium, chloride, or calcium, and could not be characterized as a membrane potential change. The second component of the response, which was inhibited by both Mg2+ (10 mM)-EGTA (10 mM) and high external potassium, was compatible with a membrane hyperpolarization. The data indicate that chemotactic factors produce changes in dye fluorescence which can, at least in part, be attributed to a hyperpolarizing membrane potential change occurring across the plasma membrane.

Albumins↗
PubMed1979

Electrophysiological properties of human oviduct smooth muscle cells in dissociated cell culture.

Intracellular recordings were made from human oviduct smooth muscle maintained in cell culture. Solitary cells isolated from one another and cells in contact with one another retained electrical properties of smooth muscle in vivo. Membrane potential of solitary cells and connected cells was -35 mV. Connected cells formed electrotonic junctions which transmitted current from one cell to another. This current spread was responsible for differences in input resistance and time constant in solitary cells, 66 Momega and 96 msec, compared to connected cells, 26 Momega and 56 msec. All cells expressed delayed rectification to depolarizing current pulses. Some cells generated action potentials spontaneously or in response to intracellular current pulses. Action potentials were abolished by cobalt or by EGTA. Slow wave potentials, 5 . 20 mV in amplitude, occurred continuously once every 15 to 45 seconds in connected cells.

Action Potentials↗
PubMed1979

Characterization of an 11,000-dalton beta-bungarotoxin: binding and enzyme activity on rat brain synaptosomal membranes.

The binding and phospholipase A2 activity of an 11,000-dalton beta-bungarotoxin, isolated from Bungarus multicincutus venom, have been characterized using rat brain subcellular fractions as substrates. 125I-labeled beta-bungarotoxin binds rapidly (k = 0.14 min-1 and 0.11 min-1), saturably (Vmax = 130.1 +/- 5.0 fmoles/mg and 128.2 +/- 7.1) fmoles/mg), and with high affinity (apparent Kd = 0.8 +/- 0.1 nM and 0.7 +/- 0.1 nM) to rat brain mitochondria and synaptosomal membranes, respectively, but not to myelin. The binding to synaptosomal membranes is inhibited by divalent cations and by pretreatment with trypsin. The binding results suggest that the toxin binds to specific protein receptor sites on presynpatic membranes. The 11,000-dalton toxin rapidly hydrolyzes synaptosomal membrane phospholipids to lysophosphatides and manifests relative substrate specificity in the order phosphatidyl ethanolamine greater than phosphatidyl choline greater than phosphatidyl serine. These results indicate that the 11,000-dalton beta-bungarotoxin is a phospholipase A2 and can use presynaptic membrane phospholipids as substrates. The binding, phospholipase activity and other biological properties of the 11,000-dalton toxin are contrasted with those of the beta-bungarotoxin found in highest concentration in the venom (the 22,000-dalton beta-bungarotoxin), and the two toxins are shown to have qualitatively similar properties. Finally the results are shown to support the hypothesis that beta-bungarotoxins act in a two-step fashion to inhibit transmitter release: first, by binding to a protein receptor site on the presynatic membrane associated with Ca2+ entry, and second, by perturbing through enzymatic hydrolyses the phospholipid matrix of the membrane and thereby causing an increase in passive Ca2+ permeability.

Animals↗
PubMed1978

Purification and biochemical characterization of an 11 000-dalton beta-bungarotoxin.

The chromatographic separation and biochemical characterization of a beta-bungarotoxin is described. This toxin is isolated as the most basic eluting protein of Bungarus multicinctus venom when separated by column chromatography on CM-Sephadex C-25. The protein migrated as a single band on pH 4.3 and sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The molecular weight of this toxin was estimated to be 10 000 +/- 1000 by analytical sedimentation analysis. This value was consistent with the electrophoretic mobility of the toxin in SDS-polyacrylamide gels. The amino acid composition of this 11 000-dalton beta-bungarotoxin was similar to that of the 22 000-dalton beta-bungarotoxin previously reported (Lee et al. (1972) J. Chromatogr. 72, 71--82; Kelly, R.B. and Brown, III, F.R. (1974) J. Neurobiol. 5, 135--150; Kondo et al. (1978) J. Biochem. Tokyo 83, 91--99), suggesting that the 11 000-dalton toxin may be one of the polypeptide chains of the larger toxin. The 11 000-dalton beta-bungarotoxin was toxic to mice when injected intravenously. Animals that received lethal doses exhibited hyperexcitability followed by ataxia, convulsions, and death. The minimum lethal dose was 0.12 microgram/g body weight. This beta-bungarotoxin exhibited Ca2+-dependent phospholipase A activity comparable to that of the 22 000-dalton beta-bungarotoxin. The enzyme exhibited phospholipid substrate specificity in the rank order of phosphatidyl-choline, phosphatidylserine, phosphatidylethanolamine, and phosphatidyl-inositol. The enzyme activity was destroyed by boiling for 3 min at pH 8.6. In addition, an enzymatically inactive quantity of the 11 000-dalton toxin, equivalent to five times the minimum lethal dose of enzymatically active toxin, was not lethal when injected into mice. To test whether phospholipase A activity is responsible for lethality, bee venom phospholipase A2 was injected into mice at similar and greater concentrations with no toxic effect. Thus, while phospholipase A activity may be required for the lethal effect of the 11 000-dalton beta-bungarotoxin, the specificity of action of the toxin is not determined by its enzyme activity.

Amino Acids↗
PubMed1978

Blockade of neuromuscular transmission by enzymatically active and inactive beta-bungarotoxin.

beta-Bungarotoxins have been shown to be presynaptic blockers of neuromuscular transmission. This paper reports experiments using the most positively charged beta-bungarotoxin that elutes from a CM-Sephadex C-25 column. The toxin is shown to be a single polypeptide with a molecular weight of approximately 11,000 and has phospholipase A2 activity. The application of the enzymatically active toxin to the frog sciatic nerve-sartorius muscle preparation results in an initial decrease in the average endplate potential amplitude followed by a temporary rebound in endplate potential amplitude, and finally a complete inhibition of endplate potentials. Similarly, minature endplate potential frequency is initially reduced upon toxin application but then increases dramatically. After the phospholipase A2 of the toxin is inactivated, treatment with the toxin results in only the initial decrease in transmitter release. There results suggest that this beta-bungarotoxin acts in two functionally separate steps: (i) by binding to a specific presynaptic site possibly associated with calcium entry, and (ii) by perturbing the presynaptic membrane by its enzyme action, which results in an increase and then a failure in transmitter release.

Action Potentials↗
PubMed1978

Immune surveillance and tumors of the nervous system.

The theory of immune surveillance postulates that one function of the immune system is to eliminate small numbers of malignant cells that arise spontaneously within the organism. Although there has been a great deal of both clinical and experimental evidence in favor of thistheory as it applies to general oncology, the question of whether or not such a surveillance system would be effective for tumors arising within the nervous system has never been studied. The young of pregnant rats which had been exposed to the neurocarcinogen ethylnitrosourea (ENU) were divided into control, immunosuppressed, and immunoenhanced groups. These lifetime alterations of the immune system had no effect on the course of nervous system tumor fromation. We believe that the most likely explanation for our results is that the "immunological privilege" of the brain prevents the usual interaction of the neoplasm and the immune system from occurring.

Animals↗
PubMed1977

Characterization of a depolarizing dopamine response in a vertebrate neuronal somatic cell hybrid.

The physiology and pharmacology of a depolarizing dopamine response was studied in the vertebrate neuronal somatic cell hybrid TCX11. The average resting membrane potential was -50 mV (S.D.=+/-7) with a membrane resistance of 40.5 mOhms (S.D.=+/-8) as determined from intracellular recordings. Depolarizing current pulses did not elicit an action potential. Cells displayed a linear current-voltage relationship when artificially depolarized up to +30 mV. Iontophoretically applied dopamine elicited a depolarizing response with a conductance increase and a reversal potential of -15 mV (S.D.=+/-4.7). Experiments altering medium ion concentrations demonstrated the conductance increase was to sodium and most likely potassium. The dopamine agonist ET495 (Piribedil) and the analogue epinine mimicked dopamine, while closely related biogenic amines, with the exception of noradrenaline, elicited no response. Apomorphine also elicited a depolarizing response but was much less efficacious than Piribedil. Noradrenaline was less potent than dopamine and appeared to act at the dopamine receptor. Methylation (3-methoxytyramine) or absence of the 3-hydroxy group (tyramine) of dopamine resulted in total loss of activity. The dopamine antagonists chlorpromazine, trifluoperazine, promazine, and bulbocapnine reversibly blocked the response to dopamine at medium concentrations less than 5 micronM. The adrenergic antagonist phentolamine blocked the response while phenoxybenzamine only reduced the response at higher concentrations. The acetylcholine antagonists alpha-bungarotoxin, hexamethonium, and scopolamine did not block the dopamine response. Both d-tubocurarine and atropine acted as antagonists. Collectively, these results demonstrate the presence of a receptor on a cultured cell line that is specific for dopamine, mediates a depolarizing and conductance increase response to dopamine, and displays the pharmacology most closely associated with dopamine receptors.

Acetylcholine↗