Functional Expression and Characterization of Skeletal Muscle Dihydropyridine Receptors in Xenopus Oocytes

Dejian Ren; Linda M. Hall

doi:10.1074/jbc.272.36.22393

Functional Expression and Characterization of Skeletal Muscle Dihydropyridine Receptors in Xenopus Oocytes*

Dejian Ren‡,§¶ and
Linda M. Hall‡‖

From the ^‡State University of New York, Department of Biochemical Pharmacology, Buffalo, New York 14260-1200 and the ^§Department of Biophysics, State University of New York at Buffalo, Buffalo, New York 14214

Abstract

Dihydropyridine receptors in vertebrate skeletal muscle serve a dual role: as voltage sensors for excitation-contraction coupling and as voltage-activated calcium channels. Although they were the first of six classes of calcium channels to be cloned, skeletal muscle dihydropyridine receptors remain the only ones not functionally expressed as calcium channels in Xenopus oocytes, leading to the hypothesis that an interacting component is missing. Using β_1b, an isoform previously found in brain, we have for the first time reconstituted skeletal muscle calcium channel function in Xenopus oocytes. We show that this β subunit is necessary for functional expression and that the α₂δ subunit significantly enhances the expressed current. The majority of the α₁ subunit in skeletal muscle is a truncated form. Here we show that both the full-length and truncated forms produce functional calcium channels in Xenopus oocytes, but the truncated form gives significantly larger currents. In addition, we show that the β_1b transcript is expressed in rat skeletal muscle, although at a much lower level than the abundant β_1a isoform.

Footnotes

↵* This work was supported by National Institutes of Health Merit Award HL39369, Muscular Dystrophy Association Grant 95-011, and an American Cancer Society Scholar Award (to L. M. H.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¶ Present address: Harvard Medical School, Rm. 1309, Enders Bldg., 320 Longwood Ave., Boston, MA 02115.
↵‖ To whom correspondence should be addressed: State University of New York, Dept. of Biochemical Pharmacology, 329 Hochstetter Hall, Buffalo, NY 14260-1200. Tel.: 716-645-2834; Fax: 716-645-3871; E-mail:LMHALL{at}acsu.buffalo.edu.