Voltage-dependent Ca²⁺ channels (Ca_V) form an important route for Ca²⁺ entry into cells upon deviations from the cell's resting membrane potential.  There are ten Ca_V α₁ subunit genes, divided into three subfamilies on both a functional and sequence homology basis. The Ca_V1 subfamily includes four genes which encode the L-type channels, the Ca_V3 subfamily includes three genes encoding the T-type channels and the Ca_V2 subfamily consists of three isoforms encoding P/Q- , N- and R-type channels, with all three contributing to neurotransmitter release in neurons.