A purified toxin (the B5 fraction) from black widow spider venom added to the solution on one side of a lipid bilayer membrane interacts irreversibly with the membrane to produce a continuous, linear rise of membrane conductance with time. Conductances greater than 10-4 reciprocal ohm per square centimeter can eventually be attained without any loss of membrane stability. Membranes treated with toxin are ideally selective for alkali cations over unions and are substantially permeable to calcium ion. These effects of the toxin result from the formation of permanent channels in the membrane of uniform conductance, 3.6 × 10-10 reciprocal ohm (in 0.1 molar potassium chloride), that remain open almost all the time. Both the divalent cation permeability and the smaller conductances at low pH of toxin-treated membranes suggest that there is negative charge (possibly from carboxyl groups) associated with the channels. We discuss the possible relation of the action of this toxin on lipid bilayer membranes to its ability to stimulate massive transmitter release at the neuromuscular junction and to produce profound morphological changes on tissue cultured neurons.
ASJC Scopus subject areas