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KEY POINTS: In arterial smooth muscle, Ca(2+) sparks are elementary Ca(2+)‐release events generated by ryanodine receptors (RyRs) to cause vasodilatation by opening maxi Ca(2+)‐sensitive K(+) (BK(Ca)) channels. This study elucidated the contribution of T‐type Ca(v)3.2 channels in caveolae and their functional interaction with L‐type Ca(v)1.2 channels to trigger Ca(2+) sparks in vascular smooth muscle cells (VSMCs). Our data demonstrate that L‐type Ca(v)1.2 channels provide the predominant Ca(2+) pathway for the generation of Ca(2+) sparks in murine arterial VSMCs. T‐type Ca(v)3.2 channels represent an additional source for generation of VSMC Ca(2+) sparks. They are located in pit structures of caveolae to provide locally restricted, tight coupling between T‐type Ca(v)3.2 channels and RyRs to ignite Ca(2+) sparks. ABSTRACT: Recent data suggest that T‐type Ca(v)3.2 channels in arterial vascular smooth muscle cells (VSMCs) and pits structure of caveolae could contribute to elementary Ca(2+) signalling (Ca(2+) sparks) via ryanodine receptors (RyRs) to cause vasodilatation. While plausible, their precise involvement in igniting Ca(2+) sparks remains largely unexplored. The goal of this study was to elucidate the contribution of caveolar Ca(v)3.2 channels and their functional interaction with Ca(v)1.2 channels to trigger Ca(2+) sparks in VSMCs from mesenteric, tibial and cerebral arteries. We used tamoxifen‐inducible smooth muscle‐specific Ca(v)1.2(−/−) (SMAKO) mice and laser scanning confocal microscopy to assess Ca(2+) spark generation in VSMCs. Ni(2+), Cd(2+) and methyl‐β‐cyclodextrin were used to inhibit Ca(v)3.2 channels, Ca(v)1.2 channels and caveolae, respectively. Ni(2+) (50 μmol L(−1)) and methyl‐β‐cyclodextrin (10 mmol L(−1)) decreased Ca(2+) spark frequency by ∼20–30% in mesenteric VSMCs in a non‐additive manner, but failed to inhibit Ca(2+) sparks in tibial and cerebral artery VSMCs. Cd(2+) (200 μmol L(−1)) suppressed Ca(2+) sparks in mesenteric arteries by ∼70–80%. A similar suppression of Ca(2+) sparks was seen in mesenteric artery VSMCs of SMAKO mice. The remaining Ca(2+) sparks were fully abolished by Ni(2+) or methyl‐β‐cyclodextrin. Our data demonstrate that Ca(2+) influx through Ca(V)1.2 channels is the primary means of triggering Ca(2+) sparks in murine arterial VSMCs. Ca(V)3.2 channels, localized to caveolae and tightly coupled to RyR, provide an additional Ca(2+) source for Ca(2+) spark generation in mesenteric, but not tibial and cerebral, arteries. |
