Allosteric Voltage Gating of Potassium Channels II: Mslo Channel Gating Charge Movement in the Absence of Ca2+

摘要: Large-conductance Ca(2+)-activated K(+) channels can be activated by membrane voltage in the absence of Ca(2+) binding, indicating that these contain an intrinsic sensor. The properties this sensor and its relationship to channel activation were examined studying gating charge movement from mSlo virtual (<1 nM). Charge was measured response steps or sinusoidal commands. charge-voltage (Q-V) is shallower shifted more negative voltages than voltage-dependent open probability (G-V). Both ON OFF currents evoked brief (0.5-ms) pulses appear decay rapidly (tau(ON) = 60 microseconds at +200 mV, tau(OFF) 16 -80 mV). However, Q(OFF) increases slowly with pulse duration, a large fraction develops time course comparable I(K) activation. slow onset prevents detection as component I(gON), although it represents approximately 40% total moved +140 mV. I(gOFF) slowed after depolarizations channels. Yet, majority relaxation too rapid limited closing. These results understood terms allosteric voltage-gating scheme developed preceding paper (Horrigan, F.T., J. Cui, R.W. Aldrich. 1999. Gen. Physiol. 114:277-304). model contains five (O) closed (C) states arranged parallel, kinetic steady-state exhibit multiple components associated C-C, O-O, C-O transitions.