Fig. 2.

κ-Opioids inhibited GVIA-sensitive, nicardipine-sensitive, and MVIIC-sensitive Ca²⁺current components. A, upper, Recordings from a single nerve terminal show the effects of U69,593 (traces marked with asterisks) on Ca²⁺ currents evoked by 50 msec steps to +10 mV from a holding potential of −90 mV before the application and in the presence of Ca²⁺ channel-type selective blockers. Sequential administration of GVIA (0.5 μm), nicardipine (10 μm), and MVIIC (1 μm) completely abolished whole-terminal current. The ability of U69,593 to suppress Ca²⁺ current was greatly reduced after application of each of these blockers. A, lower, Subtraction of the corresponding currents evoked before and after application of antagonists yielded pharmacologically distinguished N-, L-, and P/Q-type current components in control conditions and in the presence of U69,593. B, Relative contribution of pharmacologically distinguished N-, L-, and P/Q-type current components to the total whole-terminal current and their sensitivity to the inhibitory effect of U69,593. Bars in the graph represent the mean ± SEM of the normalized current amplitudes obtained from the number of terminals shown, examined using the experimental protocol depicted in A.