Signal Transmission and Transduction in Excitation-Contraction Coupling
For the better understanding of the molecular mechanism of E-C coupling, two key questions remain to be resolved: (a) how the excitation signal elicited in the T-tubule membrane is transmitted to the ryanodine receptor, RyR (signal transmission), and (b) how the signal transmitted from the T-tubule to the RyR is translated into the action of opening the sarcoplasmic reticulum Ca2+ channel to induce Ca2+ release and muscle contraction (signal transduction). Our recent studies on E-C coupling with the use of the isolated triads and synthetic peptides have provided several pieces of new information. It appears that the signal transmission is mediated by the voltage-controlled binding of the Thr671-Leu690 region (Trigger) of the cytoplasmic II-III loop of the dihydropyridine receptor α1 subunit to the putative activator site on the RyR. The transmitted signal is translated to the action of channel opening by mediation of rapid conformational changes occurring in the RyR. Upon T-tubule polarization the Glu724-Pro760 region of the loop (Blocker) replaces the RyR-bound Trigger. This reprimes the RyR to the original conformational state.
KeywordsSarcoplasmic Reticulum Ryanodine Receptor Excitation Signal Dihydropyridine Receptor Chimeric Peptide
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