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

We characterized the effects of intracellular Mg2+ (Mg 2+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, Kd(0), was ∼70 mM and the electric distance of the Mg2+ binding site, δ, was 0.2] than for the Kv1.5 channel [Kd(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. © EBSA 2004.