Regulation of Cardiac L-Type Calcium Current by Phosphorylation and G Proteins

Voltage-dependent Ca2+ channels play a major role in the electromechanical coupling of cardiac cells. During the plateau phase Ca2+ entry induces a Ca2+ -dependent Ca2+ release from the sarcoplasmic reticulum and con­ sequently the initiation of contraction (for review see 41). Voltage-dependent Ca2+ channels are also involved in the spontaneous impulse generation as well as in the duration of the action potentials and hence in refractoriness. Ca2+ channels are also the target of various hormones and neurotransmitters. In an Annual Review of Physiology that appeared ten years ago, Reuter (112) suggested a hypothetical scheme for the �-adrenergic control of Ca2+ chan­ nels by cAMP-dependent phosphorylation, but direct experimental evidence for this was still missing (further reviews see 90, 125, 133, 134). In the subsequent decade the concept of regulation via the signal transduction process and phosphorylation became more elaborate by analysis of the