FIG. 2.

Effects of divalent cations on beta-toxin insertion and channel conductance. The influence of Zn²⁺ (A), Cd²⁺ (B), and Mg²⁺ (C) on Na⁺ current through a BLM treated with beta-toxin is shown. In all experiments, toxin was added to the cis side of the membrane at a concentration of 10.8 nM. This concentration of beta-toxin was 12-fold lower than that used to generate the channels shown in Fig. 1 and typically did not produce significant numbers of channels for long periods of time. The divalent cations were added to the cis compartment at a final concentration of 2 mM at the times indicated. For these experiments the holding potential was −60 mV. Channel openings appear as upward deflections. Each panel represents a different membrane. (Inset) Blocking of the steady-state current, produced by multiple beta-toxin channels, by Zn²⁺ ions. Zn²⁺ was added to the cis side of the membrane to a final concentration of 5 mM. For this experiment the membrane was bathed in a symmetric solution of 100 mM NaCl, and the holding potential was maintained at +50 mV.