FIG. 11.

Typical single-channel current traces of X-InsP₃R-1 in various [Mg²⁺] and [ATP]_free. A: current trace was recorded at optimal (6.2 μM) [Ca²⁺]_i and saturating (10 μM) [InsP₃] in the absence of ATP and Mg²⁺.[Modified from Mak et al. (279).] The remaining current traces were recorded at 0.25 μM [Ca²⁺]_i and saturating [InsP₃] (10 μM). [Modified from Mak et al. (281).] B: [ATP]_free = 0.5 mM, [Mg²⁺] = 0 mM. C: [ATP]_free = 0 mM, [Mg²⁺] = 0 mM. D: [ATP]_free = 0 mM, [Mg²⁺] = 3 mM. E: total [ATP] = 0.5 mM, [Mg²⁺] = 3 mM, [ATP]_free = 12 μM calculated by MaxChelator software (29). F: total [ATP] = 4.8 mM, [Mg²⁺] = 3 mM, [ATP]_free = 1.9 mM calculated by MaxChelator. Arrows indicate closed-channel current level in the traces. Channel P_o evaluated for the single-channel patch-clamp experiments yielding the current traces shown in A–F are 0.79, 0.46, 0.10, 0.10, 0.10, and 0.76, respectively.