Mechanism of alpha-latrotoxin action as revealed by patch-clamp experiments on Xenopus oocytes injected with rat brain messenger RNA.

Single-channel currents produced by alpha-latrotoxin from the black widow spider venom were recorded on Xenopus oocytes injected with rat brain messenger RNA fraction of 7-8 kb. Single-channel conductance varied from 3 pS to 200 pS and sublevels of similar conductance were observed at both normal and high external concentration of Ca2+. Currents reversed at 0 mV, and the channels were permeable to Ca2+, Na+ and K+ indicating non-selective cation channel produced by the toxin.

Generation of twitch tension in frog atrial fibers by Na/Ca exchange.

Electrical and mechanical responses of frog atrial trabeculae were studied simultaneously using the double-sucrose gap method. Action potentials and twitch tension could be successively generated in fibers in which the slow inward calcium channel current was not observed. As a rule, this could be obtained in the course of a long experiment (3 to 4 hours).