Fig. 3.

Ca²⁺- and calmodulin-dependent facilitation and inactivation of P/Q-type Ca²⁺channels in response to repetitive depolarizations. A, Effects of intracellular Ca²⁺ chelators (0.5 mm EGTA; n = 7; 10 mm EGTA;n = 6; 10 mm BAPTA;n = 11) and extracellular Ba²⁺(n = 8) on currents elicited by 100 Hz trains of 5 msec pulses to +10 mV (+20 mV for BAPTA; 0 mV for Ba²⁺). Points represent averaged peak currents normalized to the peak current elicited by the first pulse of the train. Every third point of the train is plotted. B, Effect of a calmodulin inhibitor (ACI; n = 8) and control peptide [ACI(F-R); n = 7] on fractional current measured as described in A with 0.5 mm intracellular EGTA and 10 mm extracellular Ca²⁺. C, The same voltage protocol described in A except that the duration of test pulses during the train was reduced to 2 msec. Recordings were with 0.5 mm intracellular EGTA (n = 9) or 10 mm BAPTA (n = 8).