[Molecular structure and functional sites of the cardiac calcium channels]

Voltage gated L-type and T-type calcium channels are electrophysiologically characterized in the cardiac tissues. L-Type calcium channels are abundant in skeletal muscle and results from molecular studies have stimulated researches on the cardiac counterpart. This paper briefly reviews the recent progress in molecular constituents and functional sites of the cardiac calcium channel. The channel is composed of five subunits, alpha 1, alpha 2, beta, gamma, and delta, at least, but heterogeneous existence of alpha 1, beta, and gamma is also observed. The 1,4-dihydropyridine binding site has been identified in the skeletal muscle and cardiac calcium channels by photoaffinity labeling. Their sites are compared in the primary structures. PKA modulation of the cardiac channel is also discussed with the respect to phosphorylation site.