Structural determinants of calcium channel subunit function

L-, Nand P-lQ-type voltage-dependent calcium channels share a common structure, and are composed o f a t least one primary a, subunit and auxiliary P and a26 subunits. Expression o f the a, subunit alone in mammalian cells usually results in small calcium currents, and these are increased many times in amplitude by coexpression o f auxiliary P and a26 subunits. The P subunit, a cytoplasmically located protein, clearly regulates the calcium current through its interaction wi th the a, subunit, altering the latter's conformation and promoting its transportation t o the plasma membrane. In the presence o f P subunits in heterologous expression systems, calcium current amplitude is comparable t o that o f native channels; the kinetic properties and voltage-dependence o f the channels also resemble those o f native calcium channels.