Carbamate-induced rhythmic activity in the guinea-pig ileum

The action of newly synthesised basic esters of alkoxy-substituted derivatives of phenylcarbamic acid was compared with that of procaine and trimecaine in the guinea-pig small intestine. Some of the carbamate local anaesthetics, in concentrations high enough to markedly suppress cholinergic twitches, elicited regular rhythmic activity of the guinea-pig ileum. This effect of the carbamates was dependent on the position of the alkoxysubstituent and was independent of the basic group (pyrrolidine, piperidine or perhydroazepine) present. Only the ortho-substituted derivatives were active. It was also found that the rhythmic activity evoked was of myogenic origin, produced by rhythmic undulations of the sodium-pump activity, accompanied by a potential-dependent change in Ca2+ permeability. It is suggested that the mechanism by which carbamates reveal this endogenous rhythm in the guinea-pig ileum could be a selective block of noncholinergic, nonadrenergic innervation or the TEA-like activity of carbamates.