High density lipoproteins increase cytoplasmic free calcium in bovine aortic endothelial cells

This study examined the mttuence of human high density ltpoproteins (HDL) on the intracellular free calcium of cultured bovine aortic endothelial cells (BAECs). Intracellular Ca²⁺ concentration ([Ca²⁺]_i) was determined by a fluorescent calcium indicator, Fura-2. It was found that, in the presence of 1 mmol/L extracellular calcium, HDL resulted in a biphasic elevation of [Ca²⁺]_i in BAECs, consisting of an initial, transient component followed by a lower, but more sustained component. Doses of HDL from 25 to 200 μg protein/ml induced marked concentration-dependent elevations of [Ca²⁺]_i in BAECs. The sustained component was abolished by deprivation of extracellular calcium or by pretreatment of endothelial cells with a calcium influx blocker, NiCl₂. HDL-induced elevation of [Ca²⁺]_i was attenuated in a concentration-dependent way by an inhibitor of calcium release, tetracaine. Repeated applications of HDL (100 μg protein/ml) markedly blunted the initial peak component of the calcium transient of BAECs. These results demonstrate that both intracellular and extracellular calcium pools are responsible for the biphasic elevation of [Ca²⁺]_i induced by HDL in cultured BAECs.