Effect of Vanadate on ATP-Induced Increase in Intracellular Calcium Ion Levels in Human Umbilical Vein Endothelial Cells

Abstract

We investigated the effect of ammonium vanadate (vanadate) on ATP-induced increases in intracellular calcium ion level ([Ca²⁺]_i) of human umbilical vein endothelial cells (HUVEC) by fluorescence confocal microscopic imaging using the Ca²⁺-sensitive probe Calcium Green 1/AM. The ATP analogue 2-methylthio-ATP (2meS-ATP), at 10 μM, significantly increased the [Ca²⁺]_i of HUVEC, and this was abolished by 1 μM thapsigargin (a calcium pump inhibitor), whereas extracellular free calcium had no effect. Vanadate at 10 μM also significantly increased the [Ca²⁺]_i of HUVEC, which was abolished by 1 μM thapsigargin. However, vanadate at 1 μM did not exert such a significant effect. We thus examined the influence of ≤1 μM vanadate for 24 h on 2meS-ATP-induced increase in [Ca²⁺]_i. Vanadate significantly reduced the action of 2meS-ATP at 1 μM but not at 0.1 μM. Endogenously released ATP is known to induce various actions on endothelial cells. The present results suggest that vanadate exerts a regulatory influence on the function of vascular endothelial cells.