Regulation of Ca2+ Channels in Vascular Smooth Muscle Cells by Cyclic Nucleotides and by G-Protein Gating

In myocardial cells, cyclic AMP (cAMP) and cyclic GMP-dependent protein kinase (PK-A) stimulate slow Ca2+ channel activity, whereas cyclic GMP (cGMP) and cGMP-dependent protein kinase (cG-PK) inhibit channel activity (reviewed in 18). Phosphorylation by protein kinase C (PK-C) also stimulates activity of the myocardial slow Ca2+ channels (5). Intracellular ATP also modulates slow Ca2+ channel activity in myocardial cells, ATP being obligatory for channel activity (7, 14). Gating of myocardial Ca2+ slow channels by Gs-protein (GTP-activated alpha subunit) has also been demonstrated (19).