Journal
BIOPHYSICAL JOURNAL
Volume 94, Issue 7, Pages 2631-2638Publisher
CELL PRESS
DOI: 10.1529/biophysj.107.116467
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Funding
- NHLBI NIH HHS [R01 HL069911] Funding Source: Medline
- NIAMS NIH HHS [AR44750, P01 AR044750] Funding Source: Medline
- NINDS NIH HHS [R01 NS024444, NS24444] Funding Source: Medline
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In skeletal muscle, the L-type voltage-gated Ca2+ channel (1,4-dihydropyridine receptor) serves as the voltage sensor for excitation-contraction (EC) coupling. In this study, we examined the effects of Rem, a member of the RGK ((R) under bar em, (R) under bar em2, (R) under bar ad, (G) under bar em/(K) under bar ir) family of Ras-related monomeric GTP-binding proteins, on the function of the skeletal muscle L-type Ca2+ channel. EC coupling was found to be weakened in myotubes expressing Rem tagged with enhanced yellow fluorescent protein (YFP-Rem), as assayed by electrically evoked contractions and myoplasmic Ca2+ transients. This impaired EC coupling was not a consequence of altered function of the type 1 ryanodine receptor, or of reduced Ca2+ stores, since the application of 4-chloro-m-cresol, a direct type 1 ryanodine receptor activator, elicited myoplasmic Ca2+ release in YFP-Rem-expressing myotubes that was not distinguishable from that in control myotubes. However, YFP-Rem reduced the magnitude of L-type Ca2+ current by similar to 75% and produced a concomitant reduction in membrane-bound charge movements. Thus, our results indicate that Rem negatively regulates skeletal muscle EC coupling by reducing the number of functional L-type Ca2+ channels in the plasma membrane.
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