Possible involvement of sodium pump in the relaxation of rat aorta induced by alpha-human atrial natriuretic polypeptide.
In order to clarify whether the sodium handling of smooth muscle is associated with the relaxing action of alpha-human atrial natriuretic polypeptide (alpha-hANP), we examined the sodium pump-related effects of alpha-hANP on rat aortic smooth muscles. Application of Ca2+ (1.0 to 10.0 mM) to the muscle preincubated in Ca2+-free, and K+-free or 0.5 mM K+ medium for 60 min induced a contraction. Pretreatment with alpha-hANP (1 x 10(-8) M) decreased the contraction evoked in 0.5 mM [K+]o but not that in K+-free medium. After a contraction was elicited by norepinephrine in K+-free solution, an addition of KCl (1.4-5.4 mM) caused a transient relaxation in a concentration-dependent manner, presumably due to the activation of electrogenic Na pump. The alpha-hANP enhanced the relaxation, which was sensitive to ouabain, and the potentiation by alpha-hANP was inversely related to the concentration of K+ added. When alpha-hANP was applied to relax the muscle precontracted by norepinephrine in the varied concentration of external K+, alpha-hANP-induced relaxation was greater in 1.4 or 2.7 mM [K+]o than in 0 or 5.4 mM [K+]o. These results suggest that the vasodilating effect of alpha-hANP is at least partially mediated by the activation of electrogenic Na, K-pump and this effect is prominent when the Na, K-pump is partially suppressed.
Sato
K
K
Department of Veterinary Pharmacology, Faculty of Agriculture, University of Miyazaki, Japan.
Murakami
K
K
Nishimura
K
K
Ito
K
K
Kangawa
K
K
Matsuo
H
H
D000818:Animals; D001013:Aorta, Thoracic; D009320:Atrial Natriuretic Factor / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*
D009320:Atrial Natriuretic Factor; D012964:Sodium; D011188:Potassium; D009638:Norepinephrine