Positive Feedback Regulation of Agonist-Stimulated Endothelial Ca2+ Dynamics by KCa3.1 Channels in Mouse Mesenteric Arteries

Objective-Intermediate and small conductance K-Ca channels IK1 (K(Ca)3.1) and SK3 (K(Ca)2.3) are primary targets of endothelial Ca2+ signals in the arterial vasculature, and their ablation results in increased arterial tone and hypertension. Activation of IK1 channels by local Ca2+ transients from internal stores or plasma membrane channels promotes arterial hyperpolarization and vasodilation. Here, we assess arteries from genetically altered IK1 knockout mice (IK1(-/-)) to determine whether IK1 channels exert a positive feedback influence on endothelial Ca2+ dynamics. Approach and Results-Using confocal imaging and custom data analysis software, we found that although the occurrence of basal endothelial Ca2+ dynamics was not different between IK1(-/-) and wild-type mice (P>0.05), the frequency of acetylcholine-stimulated (2 mu mol/L) Ca2+ dynamics was greatly decreased in IK1(-/-) endothelium (515 +/- 153 versus 1860 +/- 319 events; P<0.01). In IK1(-/-)/SK3(T/T) mice, ancillary suppression (+Dox) or overexpression (-Dox) of SK3 channels had little additional effect on the occurrence of events under basal or acetylcholine-stimulated conditions. However, SK3 overexpression did restore the decreased event amplitudes. Removal of extracellular Ca2+ reduced acetylcholine-induced Ca2+ dynamics to the same level in wild-type and IK1(-/-) arteries. Blockade of IK1 and SK3 with the combination of charybdotoxin (0.1 mu mol/L) and apamin (0.5 mu mol/L) or transient receptor potential vanilloid 4 channels with HC-067047 (1 mu mol/L) reduced acetylcholine Ca2+ dynamics in wild-type arteries to the level of IK1(-/-)/SK3(T/T)+Dox arteries. These drug effects were not additive. Conclusions-IK1, and to some extent SK3, channels exert a substantial positive feedback influence on endothelial Ca2+ dynamics.