Abstract
The present study was undertaken to investigate the role of cyclic AMP and cyclic GMP in the regulation of the contraction-relaxation cycle in isolated smooth muscle cells from guinea pig taenia caeci. The contraction of isolated smooth muscle cells induced by both caffeine (4 X 10(-3) M) and carbachol (10(-4) M) consisted of an initial activation phase and a following spontaneous relaxation phase. Isoproterenol (10(-4) M) inhibited the carbachol-induced contraction and raised intracellular cyclic AMP level of isolated smooth muscle cells. Both the inhibition of the carbachol-induced contraction and the rise in cyclic AMP level elicited by isoproterenol were blocked by propranolol (10(-4) M). Caffeine increased intracellular cyclic AMP level significantly and contracted isolated smooth muscle cells. Caffeine and carbachol contracted isolated smooth muscle cells and increased intracellular cyclic GMP level. Cyclic GMP was significantly increased in spontaneous relaxation phase. The data suggest that beta-adrenergic inhibitory effect on cholinergic excitation in the mammalian isolated smooth muscle cells is mediated by the change in intracellular cyclic AMP level and that cyclic GMP related to the relaxation in these single cells. Thus, it appears that caffeine-induced contraction might be due to the stimulation of Ca2+-induced Ca2+ release by cyclic AMP.
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