Alexander Mauro

Double mode of action of black widow spider venom on frog neuromuscular junction.

SummaryBlack widow spider venom (BWSV) contains a toxin, α-latrotoxin, which is capable of stimulating vesicle release, resulting eventually in depletion of vesicles and block of neuromuscular transmission at the frog neuromuscular junction. Since it has been shown that α-latrotoxin very markedly increases the cation conductance of artificial lipid bilayers, it was postulated that BWSV stimulates release by opening channels permeable to Ca2+ and, in the case of Ca2+-free Ringers, to Na+ which would release Ca2+ from intracellular stores. To test this hypothesis we chose as a sodium substitute, glucosamine, which is impermeable to the venom-induced channels in the lipid bilayers and to the postsynaptic membrane of the frog neuromuscular junction. Electron microscopical analysis showed that up to 75 min perfusion in Na+ and Ca2+-free medium did not alter the ultrastructure of the nerve terminals. However when BWSV was applied in this medium a significant depletion was noticeable within 15 min and after 60 min the terminals were depleted of vesicles whereas the mitochondria were unchanged in number and structure. If BWSV is applied for 60 min in glucosamine Ringers containing 1.8 mM Ca2+, most of the nerve terminals still have synaptic vesicles scattered in the cytoplasm or clustered around amorphous structures and the mitochondria are swollen. Application of large doses of BWSV in low Ca2+ Ringers leads to damage of the mitochondria and to very pronounced swelling of the nerve endings, whereas this is not observed if the dose of venom is applied in Na+-free and Ca2+-free Ringers. Electrophysiological recording showed that neuromuscular transmission is already blocked after 15 min treatment with BWSV in glucosamme-Ringers. From these results we conclude that BWSV increases the conductance of the nerve terminal membrane to cations such as Na+ and Ca2+ and stimulates release by a mechanism which may not involve its ionophore property.

Osmotic Flow in a Rigid Porous Membrane

The concept of an internal pressure gradient in a rigid porous membrane has been proposed as the basis for osmotic flow. The origin of the pressure in terms of the theory of the chemical potential implies also the existence of states of negative pressure, that is, tension. These states have been observed experimentally by means of a Hepp-type osmometer.

Effect of concanavalin A on black widow spider venom activity at the neuromuscular junction: implications for mechanisms of venom action.

Concanavalin A (Con A) inhibits black widow spider venom-induced transmitter release at both tissue-cultured and adult neuromuscular junctions and also inhibits the venom-induced destruction of cultured neurites. This inhibitory action is partially or completely prevented by prior treatment with colchicine. Neither colchicine nor Con A interacts significantly with depolarization-induced transmitter release. These results are analogous to those obtained from experiments on lymphocyte surface receptor capping. They suggest that redistribution of neuronal membrane components may be a crucial step in spider venom action. This membrane redistribution appears to be modulated in neurons, as in other cell types, by microtubule-microfilament array. How such a redistribution causes increased transmitter release cannot as yet be specified. Changes in the ionic permeability of sodium and potassium were examined as likely mechanisms. Increased sodium influx (and seondary release of calcium from intracellular stores) cannot be the basis for spider venom action. Increased potassium efflux remains a possibility, but is not consistent with all of the data. Other possible mechanisms are also suggested.

Capacity Electrode for Chronic Stimulation

An electrode is described which can be used for electrical stimulation over prolonged periods without danger of contaminating tissue with electrode products. Use of a thoroughly insulated metal surface precludes all electrode processes, although a transient current can occur to stimulate the tissue.

Radio Frequency Stimulation: A Research and Clinical Tool Stimulation of excitable tissues by radio frequency induction methods is discussed

The radio frequency induction technique is now an important tool in physiological experiments and in the treatment of certain diseases. It has come to play an important role in the treatment of heart block in human patients, where medication has been ineffective. In the case of bladder stimulation, work with animals has shown that the voiding of urine can be induced by electrical stimulation. The successful use of this technique on human patients has yet to be consistently achieved, but there is reason to be optimistic.

The role of calcium ions in the suppression of the photoresponse during anoxia and application of metabolic inhibitors.

Abstract In these experiments, it was found that anoxia could abolish (reversibly) the generator potential of Limulus ventral photoreceptors in the absence of extracellular calcium. When the photoreceptors were poisoned with the metabolic inhibitor DNP, which has similar effects to anoxia, it was found that intracellular injection of the calcium chelator EGTA could restore the amplitude of the generator potential. Anoxia and DNP may exert their effects by raising the intracellular calcium ion concentration.