Functional Tuning of Intrinsic Endothelial Ca2+ Dynamics in Swine Coronary Arteries

Rationale: Recent data from mesenteric and cerebral beds have revealed spatially restricted Ca2+ transients occurring along the vascular intima that control effector recruitment and vasodilation. Although Ca2+ is pivotal for coronary artery endothelial function, spatial and temporal regulation of functional Ca2+ signals in the coronary endothelium is poorly understood. Objective: We aimed to determine whether a discrete spatial and temporal profile of Ca2+ dynamics underlies endothelium-dependent relaxation of swine coronary arteries. Methods and Results: Using confocal imaging, custom automated image analysis, and myography, we show that the swine coronary artery endothelium generates discrete basal Ca2+ dynamics, including isolated transients and whole-cell propagating waves. These events are suppressed by depletion of internal stores or inhibition of inositol 1,4,5-trisphosphate receptors but not by inhibition of ryanodine receptors or removal of extracellular Ca2+. In vessel rings, inhibition of specific Ca2+-dependent endothelial effectors, namely, small and intermediate conductance K+ channels (K(Ca)3.1 and K(Ca)2.3) and endothelial nitric oxide synthase, produces additive tone, which is blunted by internal store depletion or inositol 1,4,5-trisphosphate receptor blockade. Stimulation of endothelial inositol 1,4,5-trisphosphate-dependent signaling with substance P causes idiosyncratic changes in dynamic Ca2+ signal parameters (active sites, event frequency, amplitude, duration, and spatial spread). Overall, substance P-induced vasorelaxation corresponded poorly with whole-field endothelial Ca2+ measurements but corresponded precisely with the concentration-dependent change in Ca2+ dynamics (linearly translated composite of dynamic parameters). Conclusions: Our findings show that endothelium-dependent control of swine coronary artery tone is determined by spatial and temporal titration of inherent endothelial Ca2+ dynamics that are not represented by tissue-level averaged Ca2+ changes.