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Biophys J, May 2001, p. 2207-2215, Vol. 80, No. 5

Inwardly Rectifying Current-Voltage Relationship of Small-Conductance Ca2+-Activated K+ Channels Rendered by Intracellular Divalent Cation Blockade

Heun Soh and Chul-Seung Park

Department of Life Science, Kwangju Institute of Science and Technology (K-JIST), Kwangju 500-712, Korea

Small conductance Ca2+-activated K+ channels (SKCa channels) are a group of K+-selective ion channels activated by submicromolar concentrations of intracellular Ca2+ independent of membrane voltages. We expressed a cloned SKCa 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 SKCa 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 SKCa channels by altering the I-V relationship as well as activates the channel by interacting with the gating machinery, calmodulin, and SKCa channels can be considered as Ca2+-activated inward rectifier K+ channels.

Biophys J, May 2001, p. 2207-2215, Vol. 80, No. 5
© 2001 by the Biophysical Society   0006-3495/01/05/2207/09  $2.00


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