Figure 4.

Effect of P-CTX-1b on action potentials recorded under current-clamp conditions (holding potential: −90 mV) in a cultured rat myotube using the nystatin perforated patch technique. Depolarizing current pulses of 10 ms duration and increasing intensity (in steps of 200 pA) were applied before (a), and after addition of 2 nM (b) or 10 nM P-CTX-1b (c) to the external physiological solution. Note, that using the same pulse-protocol (0.25 Hz) the threshold potential for action potential generation was attained in the fifth pulse during controls (a), and during the third and second pulse in the presence of 2 and 12 nM P-CTX-1b respectively (b and c). The dashed line indicates the zero membrane potential level, the continuous solid line indicates as reference the −95 mV membrane potential. Evoked (arrows) and repetitive spontaneous action potentials (d), and spontaneous transient membrane depolarization (arrow heads) and action potentials (e), recorded from the same myotube at a holding membrane potential of −90 mV after toxin addition.