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 sarcoplasmic reticulum and ultimately results in muscle contraction. Long-lasting (L-type) calcium channels belong to the 'high-voltage activated' (HVA) group

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 STAC, STAC2 and STAC3 (via their SH3 domains) (PubMed:29078335).

Interacts with CALM (PubMed:19473981)

Skeletal muscle specific

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

• Periodic paralysis hypokalemic 1 (HOKPP1)

  An autosomal dominant disorder manifested by episodic flaccid generalized muscle weakness associated with falls of serum potassium levels.

• Malignant hyperthermia 5 (MHS5)

  Autosomal dominant disorder that is potentially lethal in susceptible individuals on exposure to commonly used inhalational anesthetics and depolarizing muscle relaxants.

• Thyrotoxic periodic paralysis 1 (TTPP1)

  A sporadic muscular disorder characterized by episodic weakness and hypokalemia during a thyrotoxic state. It is clinically similar to hereditary hypokalemic periodic paralysis, except for the fact that hyperthyroidism is an absolute requirement for disease manifestation. The disease presents with recurrent episodes of acute muscular weakness of the four extremities that vary in severity from paresis to complete paralysis.

  Attacks are triggered by ingestion of a high carbohydrate load or strenuous physical activity followed by a period of rest. Thyrotoxic periodic paralysis can occur in association with any cause of hyperthyroidism, but is most commonly associated with Graves disease.

• Congenital myopathy 18 (CMYO18)

  A congenital myopathy of variable severity, ranging from severe fetal akinesia to milder forms of muscle weakness. Most affected individuals show delayed motor development with generalized hypotonia and progressive axial and limb muscle weakness beginning soon after birth or in infancy. Additional features may include swallowing difficulties, external ophthalmoplegia, ptosis, high-arched palate, and respiratory insufficiency.

  Muscle biopsy shows variable morphologic abnormalities, including alveolar changes in the intermyofibrillar network, fiber size variability, focal disorganization, internal nuclei, and dilated sarcoplasmic reticulum and T-tubules. CMYO18 inheritance is autosomal dominant or recessive.