FIGURE 7.

Ca²⁺-dependence of dwell-time distributions. (A and B) Dwell-time histograms of closed (left) and open (right) dwell times of single CA-NSC channels at −40 mV membrane potential in 0.1 mM (A) and 1 mM (B) Ca_i²⁺. Events were binned at 10 bins per decade; ordinate is square-root transformed. Dead time was 1 ms, events were pooled from eight patches, and fitted to distributions with four (open times) or five (closed times) exponential components using maximum likelihood (solid lines; see Methods). Fit parameters were: 0.1 mM Ca²⁺: τ_c1 = 1.7 ± 0.2 ms, τ_c2 = 10 ± 0.7 ms, τ_c3 = 48 ± 4 ms, τ_c4 = 266 ± 37 ms, τ_c5 = 6997 ± 1420 ms, a_c1 = 0.36 ± 0.03, a_c2 = 0.38 ± 0.04, a_c3 = 0.19 ± 0.02, a_c4 = 0.057 ± 0.009, a_c5 = 0.016 ± 0.002, τ_o1 = 2.9 ± 0.4 ms, τ_o2 = 18 ± 1 ms, τ_o3 = 93 ± 11 ms, τ_o4 = 466 ± 68 ms, a_o1 = 0.32 ± 0.03, a_o2 = 0.51 ± 0.05, a_o3 = 0.13 ± 0.02, and a_o4 = 0.040 ± 0.004. 1 mM Ca²⁺: τ_c1 = 2.0 ± 0.1 ms, τ_c2 = 12 ± 0.4 ms, τ_c3 = 61 ± 3 ms, τ_c4 = 328 ± 20 ms, τ_c5 = 2175 ± 613 ms, a_c1 = 0.36 ± 0.02, a_c2 = 0.37 ± 0.02, a_c3 = 0.21 ± 0.01, a_c4 = 0.059 ± 0.004, a_c5 = 0.0025 ± 0.0001, τ_o1 = 4.2 ± 0.2 ms, τ_o2 = 21 ± 0.8 ms, τ_o3 = 106 ± 4 ms, τ_o4 = 394 ± 23 ms, a_o1 = 0.33 ± 0.02, a_o2 = 0.38 ± 0.02, a_o3 = 0.23 ± 0.01, and a_o4 = 0.063 ± 0.003. Also shown are the best fits to closed- and open-time distributions using three or four, and two or three exponential components, respectively (dotted and dashed lines).