DIHYDROPYRIDINE BINDING-SITES ON TRANSVERSE TUBULES ISOLATED FROM TRIADS OF RABBIT SKELETAL-MUSCLE

Receptors for the dihydropyridine class of Ca2+ channel antagonists are present on transverse tubules isolated by mechanical disruption of skeletal muscle triads. These observations account for the presence of nitrendipine binding sites in heavy sarcoplasmic reticulum [SR]. Nitrendipine receptors were not found in the terminal cisternae after disruption of the triad junctions. The number of sites in junctional T-tubules (27 pmol/mg) is only half that reported for transverse tubules isolated as free vesicles (pmol/mg). The presence of nitrendipine receptors in that region of the transversed tubules held in close apposition to the SR cisternae is consistent with the architectural requirements for the Ca2+ induced Ca2+ release phenomenon to be the mechanism of excitation-contraction coupling.