Zinc ions block the intracellular calcium release induced by caffeine in guinea-pig taenia caeci.
Zn2+ in low concentrations (0.005-0.1 mM) inhibited the transient contractions in response to caffeine (25 mM) in a dose-dependent manner in smooth muscle of intact guinea-pig taenia caeci. At Zn2+ concentrations higher than 0.1 mM, caffeine did not elicit any response. After saponin-treatment of the fibres, which leaves the Ca2+ storage sites intact, caffeine contraction was completely inhibited by Zn2+ at a relatively low concentration (0.003 mM). However, in Triton-X-100-treated fibres, in which the Ca2+ release sites are destroyed, the contraction could be induced in the presence of Zn2+ by an increase in Ca2+. In conclusion, Zn2+ can block the intracellular Ca2+ release from caffeine-sensitive release sites in taenia caeci.
Nasu
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Department of Veterinary Pharmacology, Faculty of Agriculture, Yamaguchi University, Japan.
D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent; D002432:Cecum / Q000187:drug effects / Q000378:metabolism*; D006168:Guinea Pigs; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D017830:Octoxynol / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012503:Saponins / Q000494:pharmacology; D015032:Zinc / Q000494:pharmacology*
D002413:Cations, Divalent; D012503:Saponins; D002110:Caffeine; D017830:Octoxynol; D015032:Zinc; D011188:Potassium; D002118:Calcium