Transient receptor potential cation channels in normal and dystrophic mdx muscle.

To investigate the defective calcium regulation of dystrophin-deficient muscle fibres we studied gene expression and localization of non-voltage gated cation channels in normal and mdx mouse skeletal muscle. We found TRPC3, TRPC6, TRPV4, TRPM4 and TRPM7 to be the most abundant isoforms. Immunofluorescent staining of muscle cross-sections with antibodies against TRP proteins showed sarcolemmal localization of TRPC6 and TRPM7, both, for mdx and control. TRPV4 was found only in a fraction of fibres at the sarcolemma and around myonuclei, while TRPC3 staining revealed intracellular patches, preferentially in mdx muscle. Transcripts of low abundance coding for TRPC5, TRPA1 and TRPM1 channels were increased in mdx skeletal muscle at certain stages. The increased Ca(2+)-influx into dystrophin-deficient mdx fibres cannot be explained by increased gene expression of major TRP channels. However, a constant TRP channel expression in combination with the well described weaker Ca(2+)-handling system of mdx fibres may indicate an imbalance between Ca(2+)-influx and cellular Ca(2+)-control.