A voltage-dependent noradrenaline-sensitive intracellular calcium store in smooth muscle cells of the guinea-pig aorta.
In this study we investigated the effects of K+ depolarization on the contractile responses of guinea-pig aortic smooth muscle to noradrenaline (NA) and caffeine (CAF) in Ca(2+)-free Krebs solution (CafKS). NA (1 microM) or CAF (10 mM) in regular CafKS induced a (termed first) phasic contraction, but responses to a second NA or CAF stimulation were significantly reduced, suggesting a depletion of the common intracellular (NA/CAF sensitive) store previously reported by investigators. After the depletion of this store (i) neither 105 mM KCl CafKS nor 10 mM CAF in this high K+ solution induced contraction; (ii) NA-induced contractions were enhanced by KCl, increasing dose dependently with KCl ranging from 25 to 105 mM; (iii) in 105 mM KCl CafKS repetitive NA stimulations elicited enhanced and nondecreasing responses equal to or greater than the first contraction, suggesting an efficient recycling of intracellular Ca2+. In the presence of 10 microM cyclopiazonic acid NA-induced contraction was enhanced, but the response to a subsequent NA stimulation in the absence of cyclopiazonic acid was greatly reduced, implying an inhibition of the Ca2+ recycling function; (iv) 2.0 mM EGTA (ethylene glycol bis-(beta-aminoethyl ether)-N,N'-tetraacetic acid) attenuated the NA-induced contractions in regular and 105 mM KCl CafKS. On the basis of the above results we propose that in the smooth muscle cells of guinea-pig aorta, there are two intracellular Ca2+ stores: a NA/CAF-sensitive store and a voltage-dependent NA-sensitive store with effective Ca2+ recycling capability.
Zhang
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Y
Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada.
Vohra
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MM
Wong
A Y
AY
D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism* / Q000502:physiology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D014662:Vasoconstrictor Agents; D002110:Caffeine; D004533:Egtazic Acid; D011189:Potassium Chloride; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine