Electrophysiological and mechanical effects of substance P and acetylcholine on rabbit aorta.
1. The mechanical and electrical properties of smooth muscle cells of the rabbit aorta were recorded simultaneously using respectively a force transducer and a 3 M-KCl-filled glass microelectrode. 2. Acetylcholine had two effects depending on concentration. At low concentration, it caused a persistent endothelium-dependent relaxation and hyperpolarization. At higher concentrations the acetylcholine endothelium-dependent relaxation summed with an endothelium-independent contraction. 3. Substance P caused a transient endothelium-dependent relaxation and hyperpolarization. 4. Acetylcholine and substance P depolarized and contracted de-endothelialized smooth muscle. When the de-endothelialized strip was pre-contracted by noradrenaline, acetylcholine depolarized the muscle but substance P did not. 5. In a 'cascade' experiment, the perfusate from an upstream intact aorta passed over a downstream de-endothelialized strip. Acetylcholine and substance P relaxed the downstream strip showing that they released an endothelial humoral factor which relaxes smooth muscle. 6. The results suggest a constant release of a factor from the endothelial cells which hyperpolarizes the smooth muscle cells in the media. Activation of acetylcholine and substance P receptors on the endothelium accelerates the release of this factor and causes vasodilatation.
Bény
J L
JL
Department of Animal Biology, University of Geneva, Switzerland.
Brunet
P C
PC
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D004730:Endothelium, Vascular / Q000502:physiology; D008564:Membrane Potentials; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D011817:Rabbits; D013373:Substance P / Q000494:pharmacology*
D013373:Substance P; D000109:Acetylcholine