The effects of theophylline and cyclic AMP on intestinal smooth muscle contractions

The effects of 10^?4-10^?3 M theopphylline, cyclic 3'5'-adenosine monophosphate (cyclic AMP), dibutyryl cyclic AMP (DBC) and theophylline plus DBC were observed on the spontaneous and potassium (K)-induced contractions of the guinea-pig taenia coli. All of the compounds inhibited spontaneous contractions as well as the phasic and tonic components of the K-contracture. The effects of cyclic AMP, a compound which will not readily penetrate the cell membrane, were similar to those of the other compounds in inhibiting the spontaneous and phasic contractions, but it was a less effective inhibitor of the tonic contracture. Inhibition of spontaneous and phasic activity may occur at the cell membrane while the inhibitory actions on the tonic contracture may depend on cellular penetration by the inhibitor. There was no evidence that theophylline and DBC have different sites of action.