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

Abstract

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⁺.