Pore-forming, alpha-1S subunit of the voltage-gated calcium channel that gives rise to L-type calcium currents in skeletal muscle. Calcium channels containing the alpha-1S subunit play an important role in excitation-contraction coupling in skeletal muscle via their interaction with RYR1, which triggers Ca(2+) release from the sarcplasmic reticulum and ultimately results in muscle contraction. Long-lasting (L-type) calcium channels belong to the 'high-voltage activated' (HVA) group. Channel activity is blocked by dihydropyridines (DHP), phenylalkylamines, and by benzothiazepines. Component of a calcium channel complex consisting of a pore-forming alpha subunit (CACNA1S) and the ancillary subunits CACNB1 or CACNB2, CACNG1 and CACNA2D1. The channel complex contains alpha, beta, gamma and delta subunits in a 1:1:1:1 ratio, i.e. it contains either CACNB1 or CACNB2 (By similarity). CACNA1S channel activity is modulated by the auxiliary subunits (CACNB1 or CACNB2, CACNG1 and CACNA2D1). Interacts with DYSF and JSRP1 (By similarity). Interacts with RYR1 (By similarity). Interacts with CALM (By similarity). Each of the four internal repeats contains five hydrophobic transmembrane segments (S1, S2, S3, S5, S6) and one positively charged transmembrane segment (S4). S4 segments probably represent the voltage-sensor and are characterized by a series of positively charged amino acids at every third position. The loop between repeats II and III interacts with the ryanodine receptor, and is therefore important for calcium release from the endoplasmic reticulum necessary for muscle contraction. The alpha-1S subunit is found in two isoforms in the skeletal muscle: a minor form of 212 kDa containing the complete amino acid sequence, and a major form of 190 kDa derived from the full-length form by post-translational proteolysis close to Phe-1690. Both the minor and major forms are phosphorylated in vitro by PKA. Phosphorylation by PKA activates the calcium channel. Belongs to the calcium channel alpha-1 subunit (TC 1.A.1.11) family. CACNA1S subfamily.