FIGURE 3.

Ca²⁺-dependence of CA-NSC gating immediately after patch excision. Kinetics of channel gating was analyzed for segments of record immediately after excision of patches into bath solutions containing various [Ca²⁺]. Membrane potential was −40 mV. P_o (A), mean opening rate (B), and closing rate (C) as a function of [Ca²⁺]_i. Plots of P_o (A) and opening rate (B) were fitted (solid lines) with the Hill equation and yielded parameters P_o,max = 0.90 ± 0.05, K_1/2 = 20 ± 3 μM, n = 1.5 ± 0.4 for P_o; and r_CO,max = 49 ± 11 s⁻¹, K_1/2 = 145 ± 112 μM, and n = 1.3 ± 0.9 for the opening rate. Plot of mean closing rate (C) was not fitted; instead, average closing rate of 3.5 ± 0.7 s⁻¹ calculated from the data over the whole range of Ca_i²⁺ is shown (solid line). Numbers of experiments: n = 3, 4, 5, 16, 8, and 13, respectively, for [Ca²⁺]_i = 1, 6, 13, 22, 113 μM, and 1 mM.