Figure 6.

Effects of Ca²⁺ and H⁺ on mean open and closed times. Symbols corresponded to pH as indicated in Fig. 1. (A) Mean closed times as a function of [Ca²⁺] and pH. Closed times decreased steeply as a function of [Ca²⁺], ∼100-fold per doubling of [Ca²⁺], consistent with an approximately sixth power relationship. Increasing [H⁺] (decreasing pH) leads to longer mean closed times. (B) In contrast, mean open times increased less than twofold with a 100-fold increase in [Ca²⁺], over pH ranging from 6.5 to 9.0. Thus, Ca²⁺ appears to increase Po by decreasing mean closed time, while H⁺ increases mean closed time, with little effect on open times.