Figure 1.

Effect of P-CTX-1b on sodium currents normalized by capacitance, obtained from a whole-cell recording in a small myotube (67 pF) with a reduced Na⁺ gradient. The pulse protocol corresponds to a sequence of voltage–clamp steps ranging from −100 to +65 mV at 15 mV increments from a holding potential of −90 mV. The external NaCl concentration was reduced to 36 mM and the remainder 109 mM was replaced by TEA-methanesulphonate. Control currents (a), and at a 1 min (b) and 9 min (c) after the addition of 10 nM P-CTX-1b to the bath. Panels a′, b′ and c′ show at an expanded time-base the same current traces shown in a, b and c. Note, in c and c′, the decrease (33%) in peak Na⁺ current after 9 min exposure to P-CTX-1b, as well as the sustained outward Na⁺ current and the large tail currents. Panel d summarizes the normalized peak Na⁺ current-voltage relationship obtained under control conditions, and after 1 and 9 min of P-CTX-1b exposure.