Effects of intracellular magnesium on Kv1.5 and Kv2.1 potassium channels

摘要

We characterized the effects of intracellular Mg2+ (Mg2+ i) on potassium currents mediated by the Kv1.5 and Kv2.1 channels expressed in Xenopus oocytes. Increase in Mg2+ i caused a voltage-dependent block of the current amplitude, apparent acceleration of the current kinetics (explained by a corresponding shift in the steady-state activation) and leftward shifts in activation and inactivation dependencies for both channels. The voltage-dependent block was more potent for Kv2.1 [dissociation constant at 0 mV, K d(0), was ~70 mM and the electric distance of the Mg2+ binding site, δ, was 0.2] than for the Kv1.5 channel [K d(0)~40 mM and δ=0.1]. Similar shifts in the voltage-dependent parameters for both channels were described by the Gouy-Chapman formalism with the negative charge density of 1 e−/100 Å2. Additionally, Mg2+ i selectively reduced a non-inactivating current and increased the accumulation of inactivation of the Kv1.5, but not the Kv2.1 channel. A potential functional role of the differential effects of Mg2+ i on the Kv channels is discussed.