Factors controlling changes in intracellular Ca2+ concentration produced by noradrenaline in rat mesenteric artery smooth muscle cells.
1. The intracellular Ca2+ concentration ([Ca2+]i) was measured in mesenteric artery smooth muscle cells using the fluorescent indicator indo-1. 2. Noradrenaline (1-10 microM) produced a transient increase in [Ca2+]i. This response was unaffected by the removal of external calcium suggesting that the bulk of the increase in [Ca2+]i produced by noradrenaline is due to release from an intracellular store. 3. The maintained application of caffeine (10 mM) produced a transient rise in [Ca2+]i. The rate of relaxation was slower than that of the noradrenaline response. If caffeine was removed at the peak of the rise in [Ca2+]i then [Ca2+]i recovered more quickly than was the case in both the maintained response to noradrenaline and that to caffeine. 4. In the presence of noradrenaline, caffeine or thapsigargin elevated [Ca2+]i. However, if thapsigargin or caffeine was added first, the subsequent application of noradrenaline did not increase [Ca2+]i, suggesting that only part of the caffeine-sensitive store is sensitive to noradrenaline. 5. The recovery of [Ca2+]i during the application of caffeine was unaffected by the removal of external sodium suggesting that Na+-Ca2+ exchange is not important in the reduction in [Ca2+]i. The addition of lanthanum (1 mM) did, however, greatly slow [Ca2+]i recovery. 6. We conclude that the three major factors responsible for removing Ca2+ ions from the cytoplasm are: (i) a caffeine- and noradrenaline-sensitive store (43%), (ii) a caffeine-sensitive but noradrenaline-insensitive store (36%), and (iii) a sarcolemmal Ca(2+)-ATPase (16%). Finally, a 5% contribution remains to be accounted for.
Baró
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Department of Veterinary Preclinical Sciences, University of Liverpool, UK.
Eisner
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D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002463:Cell Membrane Permeability / Q000187:drug effects; D004594:Electrophysiology; D007811:Lanthanum / Q000494:pharmacology; D008638:Mesenteric Arteries / Q000166:cytology / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism* / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology*; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000187:drug effects; D012964:Sodium / Q000378:metabolism; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D013729:Terpenes; D002110:Caffeine; D019284:Thapsigargin; D007811:Lanthanum; D012964:Sodium; D000252:Calcium-Transporting ATPases; D002118:Calcium; D009638:Norepinephrine