Genetic ablation of caveolin-1 modifies Ca2+ spark coupling in murine arterial smooth muscle cells

L-type, voltage-dependent calcium (Ca2+) channels, ryanodine-sensitive Ca2+ release (RyR) channels, and large-conductance Ca2+-activated potassium (K-Ca) channels comprise a functional unit that regulates smooth muscle contractility. Here, we investigated whether genetic ablation of caveolin-1 (cav-1), a caveolae protein, alters Ca2+ spark to K-Ca channel coupling and Ca2+ spark regulation by voltage-dependent Ca2+ channels in murine cerebral artery smooth muscle cells. Caveolae were abundant in the sarcolemma of control (cav-1(+/+)) cells but were not observed in cav-1-deficient (cav-1(-/-)) cells. Ca2+ spark and transient K-Ca current frequency were approximately twofold higher in cav-1(-/-) than in cav-1(+/+) cells. Although voltage-dependent Ca2+ current density was similar in cav-1(+/+) and cav-1(-/-) cells, diltiazem and Cd2+, voltage-dependent Ca2+ channel blockers, reduced transient K-Ca current frequency to similar to 55% of control in cav-1(+/+) cells but did not alter transient K-Ca current frequency in cav-1(-/-) cells. Furthermore, although K-Ca channel density was elevated in cav-1(-/-) cells, transient K-Ca current amplitude was similar to that in cav-1(+/+) cells. Higher Ca2+ spark frequency in cav-1(-/-) cells was not due to elevated intracellular Ca2+ concentration, sarcoplasmic reticulum Ca2+ load, or nitric oxide synthase activity. Similarly, Ca2+ spark amplitude and spread, the percentage of Ca2+ sparks that activated a transient K-Ca current, the amplitude relationship between sparks and transient K-Ca currents, and K-Ca channel conductance and apparent Ca2+ sensitivity were similar in cav-1(+/+) and cav-1(-/-) cells. In summary, cav-1 ablation elevates Ca2+ spark and transient KCa current frequency, attenuates the coupling relationship between voltage-dependent Ca2+ channels and RyR channels that generate Ca2+ sparks, and elevates K-Ca channel density but does not alter transient K-Ca current activation by Ca2+ sparks. These findings indicate that cav-1 is required for physiological Ca2+ spark and transient K-Ca current regulation in cerebral artery smooth muscle cells.