Handling of cytoplasmic Ca2+ by the sarcoplasmic reticulum during alpha 1-adrenoceptor-mediated contraction of rat mesenteric resistance arteries.
We investigated the role of the sarcoplasmic reticulum (SR) in the regulation of cytoplasmic Ca2+ ([Ca2+]i) during alpha 1-adrenoceptor-mediated contraction in rat mesenteric resistance arteries. Phenylephrine (PE) at 1 microM elevated the tension and [Ca2+]i measured with fura-2 in Ca(2+)-containing PSS, but did not do so in Ca(2+)-free PSS, suggesting that the contraction elicited by this concentration depends on the Ca2+ influx. Caffeine (100 mM) was shown to discharge Ca2+ in the SR, and cyclopiazonic acid (CPA, 10 microM) was shown to inhibit the Ca2+ uptake into the SR in these arteries. In resting arteries, both CPA and ryanodine (10 microM) sustainedly elevated [Ca2+]i without affecting the tension. In PE-stimulated arteries, both agents caused transient increase in [Ca2+]i, which was larger than that in resting arteries, and augmented the contraction. In the presence of PE, the caffeine-evoked [Ca2+]i transient was more greatly decreased after the application of ryanodine than after CPA. The CPA-induced rise in [Ca2+]i could be ascribed to inhibition of Ca2+ buffering by the SR, and the ryanodine-induced one can be attributed to the acceleration of Ca2+ release. It is suggested that both Ca2+ release from and Ca2+ uptake into the SR are enhanced during PE-induced contraction, which depends on the transmembrane Ca2+ influx.
Department of Veterinary Pharmacology, Faculty of Agriculture, Miyazaki University, Japan.
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Naganobu
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Ito
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D005453:Fluorescence; D016257:Fura-2; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000502:physiology*; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology
D007211:Indoles; D018340:Receptors, Adrenergic, alpha-1; D012433:Ryanodine; D010656:Phenylephrine; D002110:Caffeine; D002118:Calcium; D016257:Fura-2; C000543:cyclopiazonic acid