Figure 4. Increasing [Ca²⁺] augments open probability through enhancing transition from a closed state.

Representative current traces at +40 mV are shown for experiments with pipette solutions containing either 1 μM (A) or 100 μM (B) Ca²⁺. (C) Increasing pipette [Ca²⁺] from 1 μM (black bar) to 100 μM (red bar) increased average channel open probability from 0.04 to 0.36. (D) Mean (± SE) channel open (left) and closed (right) times in the presence of either 1 μM (black bars) or 100 μM (red bars) pipette [Ca²⁺]. All points histograms for open (E, F) and closed times (G, H) were constructed for 1 μM (E, G) and 100 μM (F, H) [Ca²⁺] and fitted with single exponential functions. Time constants for open channel dwell times were unaltered, but τ_closed was 10 times longer in 1 μM Ca²⁺. Thus, higher [Ca²⁺] destabilized the closed state, thereby permitting faster transitions into the open state. *p < 0.05