LIPOPOLYSACCHARIDE SUPPRESSES THROMBIN-STIMULATED AND HISTAMINE-STIMULATED RISES IN INTRACELLULAR CALCIUM-CONCENTRATION IN HUMAN ENDOTHELIAL-CELLS

We examined the effect of LPS on thrombin-and histamine-stimulated ris es in intracellular calcium concentration ([Ca2+](i)) in cultured huma n umbilical vein endothelial cells (HUVEC). HUVEC were incubated with LPS for up to 24 h. After harvesting and labeling with Quin-2/AM, HUVE C were stimulated with thrombin or histamine, and rises in [Ca2+](i) w ere monitored. LPS (0.01-10 mu g/ml) significantly suppressed the rise in [Ca2+](i) induced by 2 U/ml thrombin or 10 mu M histamine. The deg ree of suppression was dependent on the concentration of LPS, although LPS did not change unstimulated, basal intracellular calcium levels. After HUVEC were incubated with 10 mu g/ml of LPS for 24 h, the rise i n [Ca2+](i) was measured in response to various concentrations of thro mbin (0.5, 1, 2 and 4 U/ml). The rises in [Ca2+](i) were proportional to the concentration of thrombin, and the rises in [Ca2+](i), in LPS-t reated HUVEC were significantly lower than those in control HUVEC at a ny concentration of thrombin tested. The suppressive effect of LPS on rises in [Ca2+](i) appeared after 1 h incubation of HUVEC with 10 mu g /ml LPS, and reached a maximal level after 16 h. Our results raise the possibility that LPS might alter various calcium-mediated biological responses in endothelial cells in vivo.