Regulation of transient receptor potential canonical channel 1 (TRPC1) by sphingosine 1-phosphate in C2C12 myoblasts and its relevance for a role of mechanotransduction in skeletal muscle differentiation.

Transient receptor potential canonical (TRPC) channels provide cation and Ca(2+) entry pathways, which have important regulatory roles in many physio-pathological processes, including muscle dystrophy. However, the mechanisms of activation of these channels remain poorly understood. Using siRNA, we provide the first experimental evidence that TRPC channel 1 (TRPC1), besides acting as a store-operated channel, represents an essential component of stretch-activated channels in C2C12 skeletal myoblasts, as assayed by whole-cell patch-clamp and atomic force microscopic pulling. The channel's activity and stretch-induced Ca(2+) influx were modulated by sphingosine 1-phosphate (S1P), a bioactive lipid involved in satellite cell biology and tissue regeneration. We also found that TRPC1 was functionally assembled in lipid rafts, as shown by the fact that cholesterol depletion resulted in the reduction of transmembrane ion current and conductance. Association between TRPC1 and lipid rafts was increased by formation of stress fibres, which was elicited by S1P and abolished by treatment with the actin-disrupting dihydrocytochalasin B, suggesting a role for cytoskeleton in TRPC1 membrane recruitment. Moreover, TRPC1 expression was significantly upregulated during myogenesis, especially in the presence of S1P, implicating a crucial role for TRPC1 in myoblast differentiation. Collectively, these findings may offer new tools for understanding the role of TRPC1 and sphingolipid signalling in skeletal muscle regeneration and provide new therapeutic approaches for skeletal muscle disorders.