Mechanism of contractile action of barium ion on rat aortic smooth muscle.
The mechanism of Ba2+-induced contraction has been examined in helical strips of Ca2+-depleted, 60 mM K+-depolarized rat aortae. The concentration-response curves to Ca2+ or Ba2+ were significantly potentiated by exposure to 3 X 10(-8) M Bay K 8644 (a Ca2+ channel agonist) in the order Ca2+ greater than Ba2+, suggesting an action of Ba2+ ions through potential-sensitive membrane Ca2+ channels. Exposure of strips to background concentration of Ca2+ (0.05 mM) enhanced the contractile responses to Ba2+, whereas background exposure to Ba2+ (0.1 mM) attenuated Ca2+ responses. Repeated stimulation with Ba2+ resulted in tachyphylaxis, contrary to the result when Ca2+ was used. The results suggest that Ba2+ ions enter rat aortic smooth muscle cells through Ca2+ channels and mobilize a noradrenaline-insensitive intracellular Ca2+ pool. Ba2+ may also cause a desensitization of some intracellular process.
Ebeigbe
A B
AB
Department of Physiology, College of Medical Sciences, University of Benin, Nigeria.
Aloamaka
C P
CP
D000818:Animals; D001012:Aorta, Abdominal / Q000187:drug effects; D001464:Barium / Q000494:pharmacology*; D017609:Barium Compounds; D002122:Calcium Chloride / Q000494:pharmacology; D002712:Chlorides; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D013618:Tachyphylaxis / Q000187:drug effects
D017609:Barium Compounds; D002712:Chlorides; C024986:barium chloride; D001464:Barium; D002122:Calcium Chloride