ZINC IONS BLOCK THE INTRACELLULAR CALCIUM-RELEASE INDUCED BY CAFFEINEIN GUINEA-PIG TAENIA CECI

Zn2+ in low concentrations (0.005 - 0.1 mM) inhibited the transient co ntractions in response to caffeine (25 mM) in a dose-dependent manner in smooth muscle of intact guinea-pig taenia caeci. At Zn2+ concentrat ions higher than 0.1 mM, caffeine did not elicit any response. After s aponin-treatment of the fibres, which leaves the Ca2+ storage sites in tact, caffeine contraction was completely inhibited by Zn2+ at a relat ively low concentration (0.03 mM). However, in Triton-X-100-treated fi bres, in which the Ca2+ release sites are destroyed, the contraction c ould be induced in the presence of Zn2+ by an increase in Ca2+. In con clusion, Zn2+ can block the intracellular Ca2+ release from caffeine-s ensitive release sites in taenia caeci.