FIG. 6.

Typical single-channel current traces of X-InsP₃R-1 in various cytoplasmic Ca²⁺ concentrations and saturating 10 μM InsP₃. Current traces were recorded during nuclear patch-clamp experiments at cytoplasmic Ca²⁺ concentrations as tabulated, in 0.5 mM free ATP. All current traces in this and other graphs were recorded at 20 mV. Arrows indicate closed-channel current level in all current traces. Channel open probability (P_o) was evaluated for the single-channel patch-clamp experiments yielding the current traces shown in A, B, C, and D of 0.008, 0.50, 0.89, and 0.002, respectively. [Modified from Mak et al. (282).]