Cholesterol depletion alters coronary artery myocyte Ca2+ signalling in a stimulus-specific manner

Although there is evidence that caveolae and cholesterol play an important role in myocyte signalling processes, details of the mechanisms involved remain sparse. In this paper we have studied for the first time the clinically relevant intact coronary artery and measured in situ Ca2+ signals in individual myocytes using confocal microscopy. We have examined the effect of the cholesterol-depleting agents, methyl-cyclodextrin (MCD) and cholesterol oxidase, on high K+, caffeine and agonist-induced Ca2+ signals. We find that cholesterol depletion produces a stimulus-specific alteration in Ca2+ responses; with 5-HT (10 μM) and endothelin-1 (10 nM) responses being selectively decreased, the phenylephrine response (100 μM) increased and the responses to high K+ (60 mM) and caffeine (10 mM) unaffected. Agonist-induced Ca2+ signals were restored when cholesterol was replenished using cholesterol-saturated MCD. In additional experiments, enzymatically isolated myocytes were patch clamped. We found that cholesterol depletion caused a selective modification of ion channel function, with whole cell inward Ca2+ current being unaltered, whereas outward K+ current was increased, due to BKCa channel activation. There was also a significant decrease in cell capacitance. These data are discussed in terms of the involvement of caveolae in receptor localisation, Ca2+ entry pathways and SR Ca2+ release, and the role of these in agonist signalling.