SHAKING STACK MODEL OF ION CONDUCTION THROUGH THE CA-2+-ACTIVATED K+ CHANNEL

Motivated by the results of Neyton and Miller (1988. J. Gen. Physiol. 92:549-586), suggesting that the Ca2+-activated K+ channel has four high affinity ion binding sites, we propose a physically attractive variant of the single-vacancy conduction mechanism for this channel. Simple analytical expressions for conductance, current, flux ratio exponent, and reversal potential under bi-ionic conditions are found. A set of conductance data are analyzed to determine a realistic range of parameter values. Using these, we find qualitative agreement with a variety of experimental results previously reported in the literature. The exquisite selectivity of the Ca2+-activated K+ channel may be explained as a consequence of the concerted motion of the "stack" in the proposed mechanism.