Journal
CELL CALCIUM
Volume 38, Issue 1, Pages 35-44Publisher
CHURCHILL LIVINGSTONE
DOI: 10.1016/j.ceca.2005.05.001
Keywords
FKBP12; immunophilins; dihydropyridine receptor; excitation-contraction coupling
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Funding
- NIAMS NIH HHS [AR44657] Funding Source: Medline
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FK506 and rapamycin are immunosuppressant drugs that disrupt the interaction of FK506-binding proteins (FKBPs) with ryanodine receptors (RyR1), which form homotetrameric Ca2+ release channels in the sarcoplasmic reticulum (SR) of skeletal muscle. Here, we characterized the effects of short-term treatment (2 h) of skeletal myotubes with either 20 mu M FK506 or 20 mu M rapamycin on excitation-contraction (EC) coupling, sarcolemmal dihydropyridine receptor (DHPR) function, resting intracellular Ca2+, and levels of SR Ca2+ content. Both rapamycin and FK506 produced remarkably similar effects. Specifically, both drugs reduced the maximal amplitude of voltage-gated SR Ca2+ release ((Delta F/F)(max)) by 70-75% in parallel with a 50% reduction in both maximal immobilization resistant charge movement (Q(max)) and L-type Ca2+ channel conductance (G(max)). Neither immunosupressant significantly altered steady-state levels of either resting myoplasmic Ca2+ or SR Ca2+ content. Thus, store depletion does not account for the observed reduction in Ca2+ release during EC coupling. Instead, the inhibitory effect on voltage-gated SR Ca2+ release is explained by significant reductions in both the number of functional sarcolemmal voltage sensors and the intrinsic gain of voltage-gated Ca2+ release (i.e. the maximal rate of Ca2+ release per unit gating charge). (c) 2005 Elsevier Ltd. All rights reserved.
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