Decreased number of caveolae in endothelial cells impairs the relaxation induced by acetylcholine in hypertensive rat aortas

The present study was designed to investigate the contribution of endothelial cell caveolae to vascular relaxation in aortas from a normotensive (2K) and renal hypertensive (2K-1C) rat. For that purpose, concentration–effect curves to acetylcholine were constructed in 2K and 2K-1C intact endothelium aortic rings, in the absence or in the presence of the caveolae disassembler methyl-β-ciclodextrin. The potency (pD2) and the maximum relaxant effect to acetylcholine were greater in 2K than in 2K-1C aortas. Methyl-β-ciclodextrin reduced the pD2 in 2K and the maximum relaxant effect in both 2K and 2K-1C. The quantification of the caveolae number by electronic microscopy has shown a larger number of caveolae in 2K than in 2K-1C endothelial cells, which was reduced by methyl-β-ciclodextrin in both 2K and 2K-1C. The production of NO stimulated with acetylcholine was greater in 2K than in 2K-1C endothelial cells, and this effect was impaired by methyl-β-ciclodextrin in both 2K and 2K-1C. The cytosolic Ca2+ concentration ([Ca2+]c) was simultaneously measured in endothelial and smooth muscle cells stimulated with acetylcholine by confocal image of aortic slices. Acetylcholine produced a greater [Ca2+]c increase in 2K than in 2K-1C endothelial cells, which response was inhibited by methyl-β-ciclodextrin only in 2K cells. In smooth muscle cells the reduction of [Ca2+]c was higher in 2K than in 2K-1C. This effect was inhibited by methyl-β-ciclodextrin only in 2K cells. Taken together, our results suggest that the decreased number of caveolae in the endothelial cells from 2K-1C rat aortas is involved in the impaired effect of acetylcholine on [Ca2+]c and NO.