Class A Calcium Channel Variants in Pancreatic Islets and Their Role in Insulin Secretion*
- From the Departments of Neuroscience and Physiology, and§Division of Endocrinology, Tufts University School of Medicine, Boston, Massachusetts 02111
Abstract
The initiation of insulin release from rat islet β cells relies, in large part, on calcium influx through dihydropyridine-sensitive (α1D) voltage-gated calcium channels. Components of calcium-dependent insulin secretion and whole cell calcium current, however, are resistant toL-type channel blockade, as well as to ω-conotoxin GVIA, a potent inhibitor of α1B channels, suggesting the expression of additional exocytotic calcium channels in the islet. We used a reverse transcription-polymerase chain reaction-based strategy to ascertain at the molecular level whether the α1Acalcium channel isoform was also present. Results revealed two new variants of the rat brain α1A channel in the islet with divergence in a putative extracellular domain and in the carboxyl terminus. Using antibodies and cRNA probes specific for α1A channels, we found that the majority of cells in rat pancreatic islets were labeled, indicating expression of the α1A channels in β cells, the predominant islet cell type. Electrophysiologic recording from isolated islet cells demonstrated that the dihydropyridine-resistant current was sensitive to the α1A channel blocker, ω-agatoxin IVA. This toxin also inhibited the dihydropyridine-resistant component of glucose-stimulated insulin secretion, suggesting functional overlap among calcium channel classes. These findings confirm the presence of multiple high voltage-activated calcium channels in the rat islet and implicate a physiologic role for α1A channels in excitation-secretion coupling in β cells.
Footnotes
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↵* This work was supported by National Institutes of Health MCSDA KO8 NS01923 (to B. L.), and National Institutes of Health Grants DK34447 (to A. E. B., III and Larry Moss), NS16483 (to K. D., Jacob Javits Award), and National Institutes of Health GRASP Center Grant DK34928.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.
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↵‡ To whom correspondence should be addressed: Dept. of Neuroscience, Tufts University School of Medicine, 136 Harrison Ave., Boston, MA 02111. Tel.: 617-636-6938; Fax: 617-636-0576.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) , .
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↵† Deceased.
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↵1 The abbreviations used are: nt, nucleotide(s); PCR, polymerase chain reaction; bp, base pair(s); KRB, Krebs-Ringer buffer.
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- Received November 19, 1997.
- Revision received March 2, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
