Voltage-sensitive calcium channels (VSCCs) 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 blocked by the funnel toxin (ftx) and by the omega-agatoxin-IVA (omega-aga-IVA). They are however insensitive to dihydropyridines (dhp), and omega- conotoxin-GVIA (omega-ctx-GVIA). 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.