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Mg2+ and caffeine‐induced intracellular Ca2+ release in human vascular endothelial cells

Interaction of ionized magnesium ([Mg2+]o) and caffeine in regulation of intracellular free calcium concentration ([Ca2+]i) in human aortic endothelial cells was studied using fura‐2 and digital imaging microscopy. In 1.2 mm [Mg2+]o, basal [Ca2+]i was 73.7 ± 22.4 nm, with a heterogeneous distribution within the cells. No significant changes of basal [Ca2+]i were found either when cells were treated with 10 mm caffeine or when [Mg2+]o was lowered from 1.2 mm to 0.3 mm. However, a combined superfusion of the cells with 0.3 mm [Mg2+]o and 10 mm caffeine resulted in a significant elevation of [Ca2+]i to 382.8 ± 57.1 nm, probably by release of Ca2+ from internal stores, which was attenuated by NiCl2 (1 mm). These results suggest that a Ca2+‐induced Ca2+ release mechanism is involved in regulation of [Ca2+]i in endothelial cells, which may be either regulated or modulated by Mg2+.