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Ca²⁺ Modulation of Ca²⁺ Release-Activated Ca²⁺ Channels Is Responsible for the Inactivation of Its Monovalent Cation Current

Zhengchang Su ^*, Richard L. Shoemaker ^*, Richard B. Marchase  and J. Edwin Blalock ^*

^* Department of Physiology and Biophysics and Department of Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294-0005

Correspondence: Address reprint requests to J. Edwin Blalock, PhD, University of Alabama at Birmingham, Dept. of Physiology and Biophysics, MCLM 898, 1918 University Blvd., Birmingham, AL 35294-0005. Tel.: 205-934-6439; Fax: 205-934-1446; E-mail: blalock{at}uab.edu.

The Ca²⁺ release-activated Ca²⁺ (CRAC) channel is the most well documented of the store-operated ion channels that are widely expressed and are involved in many important biological processes. However, the regulation of the CRAC channel by intracellular or extracellular messengers as well as its molecular identity is largely unknown. Specifically, in the absence of extracellular divalent cations it becomes permeable to monovalent cations with a larger conductance, however this monovalent cation current inactivates rapidly by an unknown mechanism. Here we found that Ca²⁺ dissociation from a site on the extracellular side of the CRAC channel is responsible for the inactivation of its Na⁺ current, and Ca²⁺ occupancy of this site otherwise potentiates its Ca²⁺ as well as Na⁺ currents. This Ca²⁺-dependent potentiation is required for the normal functioning of CRAC channels.

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