Effects of sphingosine 1-phosphate on excitation-contraction coupling in mammalian skeletal muscle

Sphingosine 1- phosphate ( S1P) activates a subset of plasma membrane receptors of the endothelial differentiation gene family ( EdgRs) in many cell types. In C2C12 myoblasts, exogenous S1P elicits Ca2+ transients by activating voltage- independent plasma membrane Ca2+ channels and intracellular Ca2+- release channels. In this study, we investigated the effects of exogenous S1P on voltage- dependent L- type Ca2+ channels in skeletal muscle fibers from adult mice. To this end, intramembrane charge movements ( ICM) and L- type Ca (2+) current ( I-Ca) were measured in single cut fibers using the double Vaseline- gap technique. Our data showed that submicromolar concentrations of S1P ( 100 nM) caused a similar to 10- mV negative shift of the voltage threshold and transition voltages of q(gamma) and q(h) components of ICM, and of ICa activation and inactivation. Biochemical studies showed that EdgRs are expressed in skeletal muscles. The involvement of EdgRs in the above S1P effects was tested with suramin, a specific inhibitor of Edg- 3Rs. Suramin ( 200 muM) significantly reduced, by similar to 90%, the effects of S1P on ICM and I-Ca, suggesting that most of S1P action occurred via Edg- 3Rs. Moreover, S1P at concentration above 10 muM elicited intracellular Ca2+ transients in muscle fibers loaded with the fluorescent Ca2+ dye Fluo- 3, as detected by confocal laser scanning microscopy.