Decreased endothelium-dependent hyperpolarization to acetylcholine in smooth muscle of the mesenteric artery of spontaneously hypertensive rats.

The endothelium-dependent vascular relaxation to acetylcholine (ACh) in spontaneously hypertensive rats (SHR) may be impaired because of an imbalance of endothelium-derived relaxing factor and contracting factor. However, the role of the endothelium-dependent hyperpolarization remains undetermined. We examined the ACh-induced hyperpolarization and its contribution to relaxation in arteries of SHR. Membrane potentials were recorded from the mesenteric artery trunk of 6-8-month-old male SHR and also Wistar-Kyoto (WKY) rats. Endothelium-dependent hyperpolarization to ACh was unaffected by NG-nitro-L-arginine, indomethacin, or glibenclamide; was reduced by tetraethylammonium or high K+ solution; and was enhanced by low K+ solution or methylene blue, thereby indicating that hyperpolarization is not mediated by nitric oxide (endothelium-derived relaxing factor) but is presumably mediated by a hyperpolarizing factor and is due to an opening of K+ channels that probably differ from the ATP-sensitive ones. Hyperpo...