Inwardly rectifying current-voltage relationship of small-conductance Ca2+-activated K+ channels rendered by intracellular divalent cation blockade.
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, calmodulin, and SK(Ca) channels can be considered as Ca2+-activated inward rectifier K+ channels.
Soh
H
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Department of Life Science, Kwangju Institute of Science and Technology, Kwangju 500-712, Korea.
Park
C S
CS
D000818:Animals; D001464:Barium / Q000378:metabolism; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000378:metabolism*; D002412:Cations; D003001:Cloning, Molecular; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D008274:Magnesium / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated; D011485:Protein Binding; D051381:Rats; D051640:Small-Conductance Calcium-Activated Potassium Channels; D013324:Strontium / Q000378:metabolism; D014981:Xenopus
D002412:Cations; C496899:Kcnn2 protein, rat; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D051640:Small-Conductance Calcium-Activated Potassium Channels; D001464:Barium; D008274:Magnesium; D002118:Calcium; D013324:Strontium