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J. Biol. Chem., Vol. 282, Issue 42, 30406-30413, October 19, 2007

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Zebrafish Acid-sensing Ion Channel (ASIC) 4, Characterization of Homo- and Heteromeric Channels, and Identification of Regions Important for Activation by H^+*

From the Department of Physiology II, University of Würzburg, Röntgenring 9, 97070 Würzburg, Germany

There are four genes for acid-sensing ion channels (ASICs) in the genome of mammalian species. Whereas ASIC1 to ASIC3 form functional H⁺-gated Na⁺ channels, ASIC4 is not gated by H⁺, and its function is unknown. Zebrafish has two ASIC4 paralogs: zASIC4.1 and zASIC4.2. Whereas zASIC4.1 is gated by extracellular H⁺, zASIC4.2 is not. This differential response to H⁺ makes zASIC4 paralogs a good model to study the properties of this ion channel. In this study, we found that surface expression of homomeric zASIC4.2 is higher than that of zASIC4.1. Surface expression of zASIC4.1 was much increased by formation of heteromeric channels, suggesting that zASIC4.1 contributes to heteromeric ASICs in zebrafish neurons. Robust surface expression of H⁺-insensitive zASIC4.2 suggests that zASIC4.2 functions as a homomer and is gated by an as yet unknown stimulus, different from H⁺. Moreover, we identified a small region just distal to the first transmembrane domain that is crucial for the differential H⁺ response of the two paralogs. This post-TM1 domain may have a general role in gating of members of this gene family.

Received for publication, March 14, 2007 , and in revised form, July 30, 2007.

^* This work was supported by Grant GR 1771 from the Deutsche Forschungsgemeinschaft (to S. G.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed. Tel.: 49-931-31-6046; Fax: 49-931-31-2741; E-mail: stefan.gruender{at}uni-wuerzburg.de.

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