Fig. 6.

Onset of facilitation of P/Q-type Ca²⁺ channels. A, The voltage protocol (top) and representative currenttraces (bottom) recorded with 10 mm extracellular Ca²⁺ and 0.5 mm EGTA or 10 mm BAPTA in the intracellular recording solution. Currents were elicited by test pulses to 0 mV (+10 mV for BAPTA) before (P1) and 5 msec after (P2) conditioning prepulses (+10 mV for 0.5 mm EGTA; +20 mV for 10 mm BAPTA) of the indicated durations. B, Effect of intracellular Ca²⁺ chelators (0.5 mm EGTA;n = 8; 10 mm BAPTA;n = 7) on facilitation as a function of prepulse duration. Facilitation was obtained by normalizing the peak current from P2 to that from P1. Single-exponential fits of the data are shown; only the first seven points of the data obtained with 0.5 mm EGTA were included in the fit because of the onset of inactivation after longer prepulses.C, Effect of prepulse voltage on time constants for the onset of facilitation. Mean time constants were obtained from single-exponential fits to the data in B. Shown are results obtained with intracellular solutions containing 0.5 mm EGTA or 10 mm BAPTA at the indicated prepulse voltages. The number of cells recorded for each condition is indicated in parentheses.