Relationship between cyclic AMP, phosphodiesterase activity, calcium and contraction in intestinal smooth muscle.

Abstract

AbstractEffects of contracting agents on the mechanical and the metabolic activity in smooth muscle have been studied. The contraction induced by carbacholine in colon muscle from rabbit was preceded by a decrease of the cyclic AMP content. After development of the tension, the level of cyclic AMP was increased, the phosphodiesterase activity was reduced, and the phosphorylase SaL activity and glycogenosis were stimulated. These effects were blocked by atropine but not by an adrenergic β‐blocking agent. In the Ca‐poor muscle there was a sustained decrease of the cyclic AMP content by carbacholine. Contraction induced by K+ ions showed similar metabolic actions as carbacholine and these effects were Ca++ dependent too. The contracting effect of imidazole was preceded by an activation of phosphodiesterase and by reduction of cyclic AMP. The metabolic effects induced by imidazole were not Ca++ dependent. Imidazole potentiated the contracting action of carbacholine and K+. Ca++ in the same concentrations as those activating the contractile system, inhibited the phosphodiesterase activity in homogenate of colon muscle. The relationship between cyclic AMP, Ca++ and contraction in smooth muscle is discussed.