Zinc ions block the second but not the first phasic response to repetitive application of carbachol and histamine in guinea-pig taenia caeci.

In the presence of Zn2+ (0.3 mM), carbachol (10(-6) M) or histamine (10(-5) M) induced the phasic response in guinea-pig taenia caeci while the tonic response was markedly inhibited. However, when the muscles were kept in Zn(2+)-containing medium following the first stimulation with either carbachol or histamine, neither application of carbachol nor of histamine elicited another phasic contraction. Caffeine (25 mM) did not induce contraction in the presence of Zn2+. After the washing out of caffeine in the presence of Zn2+, however, the muscle did then develop the phasic response on the application of carbachol or histamine. In conclusion, Zn2+ did not affect the carbachol or histamine-induced Ca2+ release from the storage sites. However, when Zn2+ was continuously present, Ca2+ was not supplied to the storage sites. Furthermore, carbachol and histamine mobilized a common cellular Ca2+ store, but they activated Ca2+ release channels different from the ones activated by caffeine in the Ca2+ storage sites.