Effects of intracellular magnesium on Kv1.5 and Kv2.1 potassium channels.
We characterized the effects of intracellular Mg(2+) (Mg(2+) (i)) on potassium currents mediated by the Kv1.5 and Kv2.1 channels expressed in Xenopus oocytes. Increase in Mg(2+) (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 approximately 70 mM and the electric distance of the Mg(2+) binding site, delta, was 0.2] than for the Kv1.5 channel [K(d)(0) approximately 40 mM and delta = 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 A(2). Additionally, Mg(2+) (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 Mg(2+) (i) on the Kv channels is discussed.
Tammaro
Paolo
P
Department of Pharmacy and Pharmacology, University of Bath, Bath , BA2 7AY, UK.
Smirnov
Sergey V
SV
Moran
Oscar
O
D000818:Animals; D004305:Dose-Response Relationship, Drug; D007424:Intracellular Fluid / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D051666:Kv1.5 Potassium Channel; D008274:Magnesium / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated / Q000187:drug effects / Q000378:metabolism*; D051669:Shab Potassium Channels; D014982:Xenopus laevis
D051666:Kv1.5 Potassium Channel; D024642:Potassium Channels, Voltage-Gated; D051669:Shab Potassium Channels; D008274:Magnesium