Inwardly rectifying current-voltage relationship of small-conductance Ca2+-activated K+ channels rendered by intracellular divalent cation blockade
Abstract
Small conductance Ca2+-activated K+ channels (SK(Ca) channels) are a group of K+-selective ion channels activated by submicromolar concentrations of intracellular Ca2+ independent of membrane voltages. We expressed a cloned SK(Ca) channel, rSK2, in Xenopus oocytes and investigated the effects of intracellular divalent cations on the current-voltage (I-V) relationship of the channels. Both Mg2+ and Ca2+ reduced the rSK2 channel currents in voltage-dependent manners from the intracellular side and thus rectified the I-V relationship at physiological concentration ranges. The apparent affinity of Mg2+ was changed as a function of both transmembrane voltage and intracellular Ca2+ concentration. Extracellular K+ altered the voltage dependence as well as the apparent affinities of Mg2+ binding from intracellular side. Thus, the inwardly rectifying I-V relationship of SK(Ca) channels is likely due to the voltage-dependent blockade of intracellular divalent cations and that the binding site is located within the ion-conducting pathway. Therefore, intracellular Ca2+ modulates the permeation characteristics of SK(Ca) channels by altering the I-V relationship as well as activates the channel by interacting with the gating machinery, calmo...Continue Reading
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Ca2+-activated K+ channels in murine endothelial cells: block by intracellular calcium and magnesium
Inhibition of K(Ca)2.2 and K(Ca)2.3 channel currents by protonation of outer pore histidine residues
Functional effects of auxiliary beta4-subunit on rat large-conductance Ca(2+)-activated K(+) channel
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