Ca2+ buffering function of sarcoplasmic reticulum in rat tail arteries: comparison in normotensive and spontaneously hypertensive rats.
The superficial buffer barrier function of the sarcoplasmic reticulum (SR) during rest and that during stimulation with Bay k 8644, an agonist of L-type Ca2+ channels, were compared in endothelium-denuded strips of tail arteries from 13-week-old normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR), by measuring the effects of cyclopiazonic acid (CPA) and thapsigargin that inhibit SR Ca2+-ATPase and the effect of ryanodine that depletes SR Ca2+. The addition of 10 microM CPA induced a transient contraction that was not significantly different between WKY and SHR. The CPA-induced contraction was strongly inhibited by 100 nM nifedipine and was abolished by Ca2+-free solution in both strains. Thapsigargin (100 nM) or ryanodine (10 microM) induced similar, small transient contractions in the two strains. The addition of Bay k 8644 (1-100 nM) almost failed to induce a contraction in both WKY and SHR. When the strips were preincubated with 10 microM CPA, 100 nM thapsigargin or 10 microM ryanodine, Bay k 8644 induced similar concentration-dependent contractions in the two strains. The amount of Ca2+ stored in the SR, as estimated from the 20 mM caffeine-induced contraction, was not significantly different between WKY and SHR. Our results suggest that the SR of rat tail arteries can buffer a large amount of Ca2+ that enters the cell during the rest and the Bay k 8644 stimulation, and these functions are not altered in SHR.
Nomura
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Y
Department of Pharmacology, Nagoya City University Medical School, Nagoya, Japan.
Asano
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M
D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D008297:Male; D051381:Rats; D011918:Rats, Inbred SHR / Q000378:metabolism*; D011921:Rats, Inbred WKY / Q000378:metabolism*; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D013623:Tail / Q000098:blood supply* / Q000187:drug effects / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*
D004791:Enzyme Inhibitors; D007211:Indoles; D012433:Ryanodine; D019284:Thapsigargin; D002118:Calcium; C000543:cyclopiazonic acid