The effect of alpha-latrotoxin on a synaptic connection between identified neurons in the brain of the mollusc Helix pomatia L.

The effect of alpha-latrotoxin on identified monosynaptic peptidergic contacts between identified neurons from the brain of the snail Helix pomatia L. was studied. It was found that, after extracellular application, toxin evoked an increase in the amplitude of the postsynaptic response. Neither amplitude nor duration of the action potential in a presynaptic neuron was affected. Intracellular injection of toxin into the soma of a presynaptic neuron led to a decrease in the postsynaptic current amplitude. The current induced by intracellular injection of cAMP into a postsynaptic neuron was also inhibited by extracellular or intracellular application of toxin. These data indicate that toxin evokes both an increase of transmitter release from a presynaptic neuron and a decrease in amplitude of the postsynaptic response.

[Functioning of latrotoxin channels during pH changes]. / Funktsionirovanie latrotoksinovykh kanalov pri izmenenii pH.

Using the fluorescent probe BCECP, the pH dependence of Ca2+ transport in synaptosomes along alpha-latrotoxin-formed channels, was studied. It was found that the pH value in synaptosomes is equivalent to 7.16 +/- 0.09. Acidification or alkalinization of the intracellular medium by 0.1-0.3 pH units had no appreciable influence on the Ca2+ influx along latrotoxin-formed channels. Alteration of external pH caused a parallel shift in the cytoplasmic pH in the synaptosomes. The pH decrease in the external medium down to 6.0 caused the inhibition of Ca2+ fluxes along latrotoxin-formed channels. Dissipation of the proton gradient by high concentrations of KCl in the presence of nigericin decreased the latrotoxin ability to form ionic channels without any loss in the activity of the preformed channels. The influx of bivalent cations along latrotoxin-formed channels led to alkalinization of the synaptosomal cytoplasm to pH of the external medium. This pH change did not depend on the presence of Na+ in the external medium and was blocked by cadmium.

[Effect of alpha-latrotoxin on synaptic transmission between identified neurons in Helix central nervous system]. / Deistvie alpha-latrotoksina na sinapticheskuiu peredachu mezhdu identifitsirovannymi neironami v tsentral'noi nervnoi sisteme ulitki.

An identified monosynaptic peptidergic contact between identified neurons from the brain of snail Helix pomatia L. has been used to study the effect of alpha-latrotoxin. It was found that being applied extracellularly the toxin evoked an increase of the postsynaptic response amplitude. Intracellular injection of the toxin into the soma of the presynaptic neuron led to a decrease of the postsynaptic current amplitude. Current induced by intracellular injection of cAMP into postsynaptic neuron was also inhibited either by extra- or intracellular application of the toxin. According to previous data which demonstrate similarity between the postsynaptic response and the current which was induced by intracellular injection of cAMP into postsynaptic neuron it has been proposed that the toxin evokes both an increase of the transmitter release from the presynaptic neuron and a decrease of the postsynaptic response amplitude.