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

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Abstract
L-type, voltage-dependent calcium (Ca2+) channels, ryanodine-sensitive Ca2+release (RyR) channels, and large-conductance Ca2+-activated potassium (KCa) 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 KCachannel 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 KCacurrent 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 KCacurrent frequency to ∼55% of control in cav-1+/+cells but did not alter transient KCacurrent frequency in cav-1−/−cells. Furthermore, although KCachannel density was elevated in cav-1−/−cells, transient KCacurrent 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 KCacurrent, the amplitude relationship between sparks and transient KCacurrents, and KCachannel conductance and apparent Ca2+sensitivity were similar in cav-1+/+and cav-1−/−cells. In summary, cav-1 ablation elevates Ca2+spark and transient KCacurrent frequency, attenuates the coupling relationship between voltage-dependent Ca2+channels and RyR channels that generate Ca2+sparks, and elevates KCachannel density but does not alter transient KCacurrent activation by Ca2+sparks. These findings indicate that cav-1 is required for physiological Ca2+spark and transient KCacurrent regulation in cerebral artery smooth muscle cells.