Skeletal muscle dihydropyridine (DHP) receptors function both as voltage-activated Ca2+ channels and as voltage sensors for coupling membrane depolarization to release of Ca2+ from the sarcoplasmic reticulum. In skeletal muscle, the principal or α1S subunit occurs in full-length (∼10% of total) and post-transcriptionally truncated (∼90%) forms, which has raised the possibility that the two functional roles are subserved by DHP receptors comprised of different sized α1S subunits. We tested the functional properties of each form by injecting oocytes with cRNAs coding for full-length (α1S) or truncated (α1SΔC) α subunits. Both translation products were expressed in the membrane, as evidenced by increases in the gating charge (Qmax 80–150 pC). Thus, oocytes provide a robust expression system for the study of gating charge movement in α1S, unencumbered by contributions from other voltage-gated channels or the complexities of the transverse tubules. As in recordings from skeletal muscle, for heterologously expressed channels the peak inward Ba2+ currents were small relative to Qmax. The truncated α1SΔC protein, however, supported much larger ionic currents than the full-length product. These data raise the possibility that DHP receptors containing the more abundant, truncated form of the α1S subunit conduct the majority of the L-type Ca2+ current in skeletal muscle. Our data also suggest that the carboxyl terminus of the α1S subunit modulates the coupling between charge movement and channel opening.
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1 September 2000
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August 14 2000
Cooh-Terminal Truncated Alpha1S Subunits Conduct Current Better than Full-Length Dihydropyridine Receptors
James A. Morrill,
James A. Morrill
aProgram in Neuroscience, Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115
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Stephen C. Cannon
Stephen C. Cannon
aProgram in Neuroscience, Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115
bDepartment of Neurology, Massachusetts General Hospital, Boston, Massachusetts 02114
Search for other works by this author on:
James A. Morrill
aProgram in Neuroscience, Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115
Stephen C. Cannon
aProgram in Neuroscience, Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115
bDepartment of Neurology, Massachusetts General Hospital, Boston, Massachusetts 02114
Abbreviations used in this paper: DHP, dihydropyridine; E-C, excitation–contraction.
Received:
April 20 2000
Revision Requested:
July 05 2000
Accepted:
July 18 2000
Online ISSN: 1540-7748
Print ISSN: 0022-1295
© 2000 The Rockefeller University Press
2000
The Rockefeller University Press
J Gen Physiol (2000) 116 (3): 341–348.
Article history
Received:
April 20 2000
Revision Requested:
July 05 2000
Accepted:
July 18 2000
Citation
James A. Morrill, Stephen C. Cannon; Cooh-Terminal Truncated Alpha1S Subunits Conduct Current Better than Full-Length Dihydropyridine Receptors. J Gen Physiol 1 September 2000; 116 (3): 341–348. doi: https://doi.org/10.1085/jgp.116.3.341
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