[Synaptic Processes in Smooth Muscles]

Junction potentials evoked by intramural stimulation were investigated in smooth muscles of guinea-pig gastrointestinal tract by means of intracellular recording and sucrose-gap methods. It was shown that cholinergic nerve-muscle transmission is only excitatory and more effective in fundic smooth muscles as compared with other part of the gut. Adrenergic nerve control of gastrointestinal motility is carried out both by excitation and inhibition of the smooth muscles. Nonadrenergic inhibition was observed in circular muscle layer of all parts of the gut and was more effective in distal colon. Noncholinergic, nonadrenergic excitation in caecum smooth muscles is shown to be of complex nature. It consists of an initial excitatory junction potential followed by a slow late wave of depolarization. In other parts of the gastrointestinal tract such an excitation is manifested only by a slow late wave of depolarization.