Endothelial cell calcium increases during flow-induced dilation in isolated arterioles.

The influence of flow on endothelial intracellular calcium concentration ([Ca2+]i) was determined in intact, isolated arterioles by selectively loading endothelial cells with the calcium-sensitive fluorescent dye fura-2. A fluorescence microscope coupled to a digital image processor was used to simultaneously measure fura-2 fluorescence and microvessel diameter. Flow through the arteriole significantly increased endothelial [Ca2+]i and dilated arterioles. Acetylcholine also increased in endothelial [Ca2+]i and caused vasodilation. In comparison, adenosine did not alter endothelial [Ca2+]i but dilated arterioles. Removal of the endothelium abolished the responses to flow and acetylcholine but not adenosine. These results provide strong support for the involvement of calcium in endothelium-dependent dilation of isolated arterioles by flow and agonists and emphasize the importance of studying endothelial function in intact vessels.