Fig. 2.

Voltage dependence of inactivation and recovery from inactivation of P/Q-type Ca²⁺ currents.A, The voltage protocol for measuring inactivation caused by a 1 sec conditioning prepulse is shown above representative Ca²⁺ currents evoked by a 10 msec test pulse to +20 mV after prepulses to the indicated voltages. B, The relationship between the inactivating prepulse voltage and peak Ca²⁺ currents is shown. Peak Ca²⁺currents elicited by the +20 mV test pulse after the conditioning prepulse were recorded with intracellular solutions containing 0.5 mm EGTA (closed circles;n = 6) or 10 mm BAPTA (open circles; n = 9) and were normalized to Ca²⁺ currents evoked after a −30 mV prepulse.Open inverted triangles represent the current–voltage relationship for Ca²⁺ currents (0.5 mmintracellular EGTA) elicited by test pulses to the indicated voltages without a prepulse and normalized to the current amplitude of the +10 mV test pulse (n = 8). C, Recovery from inactivation induced by a 2 sec conditioning pulse to +10 mV (+20 mV for BAPTA) was monitored using +10 mV test pulses (+20 mV for BAPTA) (6 msec) at 0.2 Hz. Test currents were normalized to the noninactivated Ca²⁺ current evoked before the inactivating prepulse. The voltage protocol is shown above the sample current records. The current during the 5 sec interval between test pulses was not recorded. D, Fractional recovery from inactivation obtained by plotting Ca²⁺ current amplitudes normalized to the noninactivated test current against time after the inactivating prepulse is shown. Intracellular recording solutions contained either 0.5 mm EGTA (n = 6) or 10 mm BAPTA (n = 5).