The effect of ionophore A23187 on albumin internalization in cultured human umbilical vein endothelial cells

The effects of calcium and the calcium ionophore A23187 on endocytosis were studied in cultured human umbilical vein endothelial cells using iodinated human albumin to measure bulk phase endocytosis. In the absence of the ionophore, varying the levels of extracellular calcium did not affect endocytosis. In the presence of 10 μM A23187, the endocytic clearance of albumin decreased approx. 50% when exposed to physiological concentrations of extracellular calcium, but increased approx. 50% at lower calcium concentrations. Since the ionophore is known to alter cellular calcium levels, these results are compatible with a role for intracellular calcium in the modulation of endothelial cell endocytosis.