Purification and Structure of L-Type Calcium Channels

Calcium channels are an essential part of the cellular signal trans duction system, since they produce changes in cytosolic calcium. Three types of voltage-dependent calcium channels (T, L, and N channels) have been identified by electrophysiological and pharmacological tech- niques. L and N-type channels have attracted intensive interest since their opening and closing is modulated by hormones, G proteins, pro- tein kinases, toxins, and drugs. The permeation of calcium through L-type channels is blocked by several organic drugs, the calcium chan- nel blockers (CaCB), including the dihydropyridines (DHP), phenylalkylamines, and benzothiazepines. Each class of CaCB binds to a specific site that is present on the α₁ -subunit of the Gtype calcium channel. The binding to these CaCB-specific sites is modulated allos terically by the membrane potential, calcium, and the occupancy of the other binding sites (1 –3 ).