Positive feedback regulation of agonist-stimulated endothelial Ca2+ dynamics by KCa3.1 channels in mouse mesenteric arteries

Abstract

OBJECTIVE - Intermediate and small conductance KCa channels IK1 (K Ca3.1) and SK3 (KCa2.3) are primary targets of endothelial Ca signals in the arterial vasculature, and their ablation results in increased arterial tone and hypertension. Activation of IK1 channels by local Ca 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 Ca dynamics. APPROACH AND RESULTS - Using confocal imaging and custom data analysis software, we found that although the occurrence of basal endothelial Ca dynamics was not different between IK1 and wild-type mice (P>0.05), the frequency of acetylcholine-stimulated (2 μmol/L) Ca dynamics was greatly decreased in IK1 endothelium (515±153 versus 1860±319 events; P<0.01). In IK1/SK3 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 Ca reduced acetylcholine-induced Ca dynamics to the same level in wild-type and IK1 arteries. Blockade of IK1 and SK3 with the combination of charybdotoxin (0.1 μmol/L) and apamin (0.5 μmol/L) or transient receptor potential vanilloid 4 channels with HC-067047 (1 μmol/L) reduced acetylcholine Ca dynamics in wild-type arteries to the level of IK1/SK3+Dox arteries. These drug effects were not additive. CONCLUSIONS - IK1, and to some extent SK3, channels exert a substantial positive feedback influence on endothelial Ca dynamics. © 2013 American Heart Association, Inc.