Differential targeting and signalling of voltage‐gated T‐type Ca v 3.2 and L‐type Ca v 1.2 channels to ryanodine receptors in mesenteric arteries

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.