Disruption of Caveolae Results in Attenuated Endothelium Dependent Relaxation
A significant pathology associated with hypertension is endothelial dysfunction caused by reduced availability of endothelial nitric oxide. There are several potential contributing mechanisms to the decreased nitric oxide availability including changes in membrane receptor function, alterations in second messenger systems, or decreases in crucial cofactors associated with enzyme regulation. Recently it has been demonstrated that endothelial nitric oxide synthase is concentrated in the caveolae of endothelial cells, presumably by formation of a heteromeric complex. The current studies hypothesize that disruption of caveolar membranes by the sterol binding agent filipin will result in the attenuation of endothelium dependent vasodilator responses. Aorta from male Sprague-Dawleys rats were removed, cleaned of adhering fat, and cut into rings for the measurement of isometric force development. Rings were incubated in the presence of filipin complex (5 ug/ml) or vehicle for one hour. To determine vasodilation all vessels were precontracted with an EC50 concentration of phenylephrine. Filipin treatment significantly attenuated endothelium dependent relaxation in response to both cholinergic activation with acetylcholine (maximum relaxation, filipin 40±7% vs. vehicle 95±2%; EC50 -5.8±.20 vs. -6.6±.03) and the Ca2+ionophore A-23187 (maximum relaxation, filipin 24±5% vs. vehicle 82±3%; EC50 -4.2±.19 vs. -6.5±.09). Maximal relaxation in response to 10-5M sodium nitroprusside was unchanged between groups. These results implicate the caveolae in endothelium dependent relaxation and suggest that the damage to the endothelium such as in hypertension may result in diminished caveolar function. This impaired caveolar function may provide a novel mechanism contributing to the reduction in nitric oxide available in hypertension.