Fig. 7. Inhibition by Som involves N- and P/Q-type channels. A, Peak current amplitudes during steps to −10 mV (holding potential, −90 mV) plotted as a function of time. Nifedipine (nif, 2 μm), Som (som, 200 nm), and Cd2+ (400 μm) were applied at times indicated bybars. Application of nifedipine reduced the peak current and changed the time course (see inset) but did not prevent a further reduction by Som. B, The bars represent mean ± SEM inhibition of IBaby Som in control conditions and after application of combinations of the calcium channel blockers nifedipine (2 μm), ω-CgTx-IVA (2 μm), and ω-Aga-IVA (100 nm). The percent inhibition has been calculated referenced to the amplitude of IBa before application of any blocker. C, Peak current amplitudes during a pulse protocol identical to A. The applications of Som (200 nm), ω-Aga-IVA (100 nm), ω-CgTx-IVA (2 μm), nifedipine (2 μm), and Cd2+ (400 μm). The insets show sample traces before Som (thick lines) and during Som (thin lines) at the times indicated. Calibration bars (A, C): 20 msec, 500 pA.