Hyperpolarization contributes to endothelium-dependent relaxations to acetylcholine in femoral veins of rats.
The contribution of membrane hyperpolarization to endothelium-dependent relaxations induced by acetylcholine was investigated in the femoral vein of the rat using a microelectrode technique and isometric tension recordings. Acetylcholine caused endothelium-dependent relaxations and hyperpolarization in tissues contracted with norepinephrine. The relaxation was sustained during a prolonged exposure to acetylcholine (less than or equal to 10 min). In contrast, the hyperpolarization declined with time. In the presence of nitro-L-arginine, a blocker of nitric oxide synthesis, the relaxation became smaller and transient, whereas the hyperpolarization was not affected. There was a temporal relationship between the relaxation and the hyperpolarization in the presence of nitro-L-arginine, when the two parameters were recorded simultaneously. In tissues contracted with 60 mM K+, in which hyperpolarization could not be observed, acetylcholine caused relaxations and these relaxations were abolished by nitro-L-arginine. The results suggest a contribution of both nitric oxide and membrane hyperpolarization to the endothelium-dependent relaxation induced by acetylcholine in the femoral vein of the rat.
Nagao
T
T
Center for Experimental Therapeutics, Baylor College of Medicine, Houston, Texas 77030.
Vanhoutte
P M
PM
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D004594:Electrophysiology; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000502:physiology; D005268:Femoral Vein / Q000187:drug effects* / Q000502:physiology; D008297:Male; D019335:Nitroarginine; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation
D019335:Nitroarginine; D001120:Arginine; D000109:Acetylcholine; D011188:Potassium; D009638:Norepinephrine