Cytosolic-free calcium in smooth-muscle and endothelial cells in an intactarterial wall from rat mesenteric artery in vitro

The regulation of cytosolic-free calcium concentration of smooth-muscle and endothelial cells was mainly studied on cultured cells where the cross tal k between these two coupled cell types is lost. In the present study, the c ytosolic-free calcium concentration in the endothelial and the smooth-muscl e cells was examined in an intact arterial wall in vitro. Strips of the mai n branch of rat mesenteric artery were used. Cytosolic-free calcium concent ration [Ca2+](i) was estimated by determining the fluorescence ratio of the two calcium probes, Fluo-4 and Fura red. The emitted fluorescence of both probes was measured with a confocal microscope. We showed that potassium an d phenylephrine, which increase the cytosolic-free calcium concentration of the smooth-muscle cells, also indirectly influence the calcium concentrati on in the endothelial cells. By simultaneously determining [Ca2+](i) in the endothelial and the smooth-muscle cells of an arterial strip, we observed that when calcium increases in the endothelial cells in response to acetylc holine, it slightly decreases in the smooth-muscle cells. We conclude that the regulation of [Ca2+](i) in the arterial endothelial cell, depends accor ding to the stimuli either upon the endothelial cells themselves, or upon t he coupled smooth-muscle cells. (C) 2001 Harcourt Publishers Ltd