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Biomedical subjects

M W Bitensky

Publications and source records attributed to M W Bitensky.

At least 91 records · Page 5Linked to original sources
PubMed1972

Digitonin effects on photoreceptor adenylate cyclase.

Adenylate cyclase is described in a number of photoreceptor membranes. Vertebrate rod outer segments contain light-regulated cyclase, and light regulation is abolished by digitonin. Disruption of microvilli in cone and rhabdomphotoreceptors is also associated with loss of light regulation and retention of full enzymic activity. The data suggest that inhibitory constraint provides regulation in cyclase systems and that disruption of membrane structure uncouples catalytic and regulatory elements.

Adenylyl Cyclases↗
PubMed1972

Biochemical characterization and cytochemical localization of a catecholamine-sensitive adenylate cyclase in isolated capillary endothelium.

Capillaries were isolated from epididymal fat, and a catecholamine-sensitive adenylate cyclase found in these capillaries was characterized. The effect of various hormones on the accumulation of adenosine 3':5'-cyclic monophosphate in capillary endothelial cells was determined and the cyclase was found to exhibit mixed alpha and beta characteristics. Cyclase was cytochemically localized in these endothelial cells with 5'-adenylyl-imidodiphosphate as a specific cyclase substrate and alloxan as a specific cyclase inhibitor. Lead imidodiphosphate was precipitated at or near the site of cyclase activity upon hydrolysis of 5'-adenylyl-imidodiphosphate by cyclase. This reaction product was observed primarily on the luminal surface of intact capillaries, in micropinocytic invaginations, in free vesicles within the cytoplasm, and in the intracellular junctions.

Adenosine Triphosphate↗
PubMed1971

Cyclic adenosine monophosphate: function in photoreceptors.

Inactivation of adenylate cyclase in outer segments of retinal photoreceptor cells is proportional to the bleaching of rhodopsin. Membranes of the outer segments also contain a particulate, light-insensitive phosphodiesterase of high specific activity. In electrophysiological experiments, application of cyclic adenosine monophosphate along with a methylxanthine mimics the effects of illumination on the photoreceptor cell of the compound eye of Limulus.

Action Potentials↗
PubMed1971

Adenyl cyclase as a link between photon capture and changes in membrane permeability of frog photoreceptors.

Tomita has shown by electrophysiological measurements that the photoreceptors of the vertebrate retina are depolarized (excited) by darkness and hyperpolarized (inhibited) by light. Excitation is accompanied by an increase, and inhibition by a decrease, in the sodiumion permeability of the receptor cell. The retinal-rod outer segments of the frog contain an adenyl cyclase that is active in darkness and inactivated by light. This cyclase has a specific activity ten-times higher than the activity in previously described tissues. It is suggested that cyclic AMP is an intermediate in the light- and dark-induced changes in sodium permeability in the photoreceptor cell.

Adenine Nucleotides↗
PubMed1966

Studies of PPLO infection. II. The neurotoxin of Mycoplasma neurolyticum.

Rolling disease has been produced and studied in rats and mice, using the exotoxin of the A strain of Mycoplasma neurolyticum. The primary lesion of the brain consists of spongiform degeneration, associated with vesicle formation in the cortex and underlying white matter of the cerebral hemispheres, and in the molecular layer of the cerebellum. The brains of animals surviving 2 days or longer show extensive necrotizing lesions resembling ischemic necrosis, in both cerebral hemispheres. The brains of rats and mice with rolling disease become deeply stained by intraperitoneally injected trypan blue, indicating early disruption of the blood brain barrier. The toxin appears to be a thermolabile protein with a molecular weight exceeding 200,000. It is only active when injected by vein, and causes no disease when injected intracerebrally, intraperitoneally or subcutaneously, suggesting the existence of specific receptors within the vascular bed of the central nervous system. Protection is afforded by rabbit antibody against the toxin, but only when antibody is injected within less than 3 min after intravenous injection of toxin, indicating rapid fixation to receptors in the brain. The toxin is inactivated by incubation for 10 min at 37 degrees C with suspensions of the sedimentable component of normal brain. The inactivating factor in brain sediment is very thermostable, not affected by trypsin, and eliminated by treatment with periodate. Similar inactivation of toxin is demonstrable with water-soluble gangliosides of brain. A theoretical concept to explain the action of the toxin is proposed.

Animals↗
PubMed1966

Studies of PPLO infection. IV. The neurotoxicity of intact mycoplasmas, and their production of toxin in vivo and in vitro.

Concentrated suspensions of washed Mycoplasma neurolyticum produce rolling disease in mice and rats, with neurological manifestations and pathological lesions similar to those seen with the exotoxin of this organism. Pretreatment of animals with tetracycline protects completely against the toxic effects of washed suspensions of mycoplasmas, while tetracycline affords no protection against the exotoxin. Freeze-thawing disruption of mycoplasma suspensions eliminates their neurotoxicity, while the same treatment does not affect exotoxin. The toxicity of intact organisms is not affected by exposure to the sedimentable component of brain, nor to ganglioside. These observations are interpreted to indicate that the neurotoxicity of living mycoplasmas must be due to their production of toxin after they have been injected into the animal. Resting mycoplasmas, suspended in Ringer's solution in dialysis sacs submerged in PPLO broth) produce considerable amounts of toxin within 15 min of incubation at 37 degrees C. Toxin is also produced, although in somewhat less amount, by washed organisms suspended in phosphate buffer containing glucose. The formation of toxin is prevented by the presence of puromycin, but not by the aminonucleoside analogue of puromycin, indicating that active protein synthesis is involved in the elaboration of toxin. The similarities between the neurotoxicity of the intact organisms of M. neurolyticum and Mycoplasma gallisepticum are discussed.

Animals↗