Voltage-sensitive calcium channels (VSCC) mediate the entry of calcium ions into excitable cells and are also involved in a variety of calcium-dependent processes, including muscle contraction, hormone or neurotransmitter release, gene expression, cell motility, cell division and cell death. The isoform alpha-1A gives rise to P and/or Q-type calcium currents. P/Q-type calcium channels belong to the 'high-voltage activated' (HVA) group and are specifically blocked by the spider omega-agatoxin-IVA (AC P30288) (PubMed:1311418). They are however insensitive to dihydropyridines (DHP). Voltage-dependent calcium channels are multisubunit complexes, consisting of alpha-1, alpha-2, beta and delta subunits in a 1:1:1:1 ratio. The channel activity is directed by the pore-forming and voltage-sensitive alpha-1 subunit. In many cases, this subunit is sufficient to generate voltage-sensitive calcium channel activity. The auxiliary subunits beta and alpha-2/delta linked by a disulfide bridge regulate the channel activity (By similarity). Interacts (via C-terminal CDB motif) with CABP1 in the pre- and postsynaptic membranes (PubMed:11865310). Interacts with the spider omega-agatoxin-IVA (AC P30288) (PubMed:1311418). Additional isoforms seem to exist. Brain specific. Purkinje cells contain predominantly P-type VSCC, the Q-type being a prominent calcium current in cerebellar granule cells. Also found in heart, in kidney distal convoluted tubule (DCT), and in pituitary. 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. Belongs to the calcium channel alpha-1 subunit (TC 1.A.1.11) family. CACNA1A subfamily.