Atherosclerosis affects calcium signalling in endothelial cells from apolipoprotein E knockout mice before plaque formation

Little is known about how hypercholesterolaemia affects Ca(2+) signalling in the vasculature of ApoE(−/−) mice, a model of atherosclerosis. Our objectives were therefore to determine (i) if hypercholesterolaemia alters Ca(2+) signalling in aortic endothelial cells before overt atherosclerotic lesions occur, (ii) how Ca(2+) signals are affected in older plaque-containing mice, and (iii) whether Ca(2+) signalling changes were translated into contractility differences. Using confocal microscopy we found agonist-specific Ca(2+) changes in endothelial cells. ATP responses were unchanged in ApoE(−/−) cells and methyl-β-cyclodextrin, which lowers cholesterol, was without effect. In contrast, Ca(2+) signals to carbachol were significantly increased in ApoE(−/−) cells, an effect methyl-β-cyclodextrin reversed. Ca(2+) signals were more oscillatory and store-operated Ca(2+) entry decreased as mice aged and plaques formed. Despite clearly increased Ca(2+) signals, aortic rings pre-contracted with phenylephrine had impaired relaxation to carbachol. This functional deficit increased with age, was not related to ROS generation, and could be partially rescued by methyl-β-cyclodextrin. In conclusion, carbachol-induced calcium signalling and handling are significantly altered in endothelial cells of ApoE(−/−) mice before plaque development. We speculate that reduction in store-operated Ca(2+) entry may result in less efficient activation of eNOS and thus explain the reduced relaxatory response to CCh, despite the enhanced Ca(2+) response.