We examined developmental changes in calcium channel α2/δ subunit mRNA in skeletal muscle and their possible influence on L-type calcium currents (ICa−L). Several isoforms of α2/δ-1 mRNA were found in myotubes and muscle fibers, and their relative levels changed with time in culture or age of the animal. Levels of α2/δ-1a were largest in older myotubes and was the only α2/δ-1 isoform present in adult muscle. Both myotubes and muscle fibers also expressed low levels of α2/δ-2 and α2/δ-3 mRNA at all ages, α2/δ-4 mRNA could not be detected in either myotubes or muscle fibers. Changes in amplitude and voltage-dependent inactivation of the ICa−L concurred with the shift in α2/δ-1 isoform message, suggesting that alternative splicing of this subunit might be important for modulation of ICa−L.