MG2-INDUCED INTRACELLULAR CA2+ RELEASE IN HUMAN VASCULAR ENDOTHELIAL-CELLS( AND CAFFEINE)

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 microsc opy. In 1.2 mM [Mg2+]o, basal [Ca2+]i was 73.7 +/- 22.4 nM, with a het erogeneous distribution within the cells. No significant changes of ba sal [Ca2+]i were found either when cells were treated with 10 mM caffe ine or when [Mg2+]o was lowered from 1.2 mM to 0.3 mM. However, a comb ined superfusion of the cells with 0.3 mM [Mg2+)o and 10 mM caffeine r esulted in a significant elevation of [Ca2+]i to 382.8 +/- 57.1 nM, pr obably by release of Ca2+ from internal stores, which was attenuated b y 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+.