The Ca_v 1.2 Ca²⁺ channel is expressed in sarcolemma of type I and IIA myofibers of adult skeletal muscle

Although Ca²⁺-dependent signaling pathways are important for skeletal muscle plasticity, the sources of Ca²⁺ that activate these signaling pathways are not completely understood. Influx of Ca²⁺ through surface membrane Ca²⁺ channels may activate these pathways. We examined expression of two L-type Ca²⁺ channels in adult skeletal muscle, the Ca_V 1.1 and Ca_V 1.2, with isoform-specific antibodies in Western blots and immunocytochemistry assays. Consistent with a large body of work, expression of the Ca_V 1.1 was restricted to skeletal muscle where it was expressed in T-tubules. Ca_V 1.2 was also expressed in skeletal muscle, in the sarcolemma of type I and IIa myofibers. Exercise-induced alterations in muscle fiber types cause a concomitant increase in the number of both Ca_V 1.2 and type IIa-positive fibers. Taken together, these data suggest that the Ca_V 1.2 Ca²⁺ channel is expressed in adult skeletal muscle in a fiber type-specific manner, which may help to maintain oxidative muscle phenotype.