abstract
- The effect of theophylline on the ATP response, the adenosine response and the inhibitory junction potential was studied on circular smooth muscle preparations of the guinea-pig stomach. The amplitude of the inhibitory junction potential evoked after stimulation of the non-cholinergic, non-adrenergic nervous system was not affected by a moderate concentration of theophylline (5 x 10(-6)-10(-5) M). At higher concentrations (5 x 10(-5)-10(-3) M) theophylline relaxed the muscle hyperpolarized the cell membrane and reduced the inhibitory junction potential slightly. ATP and adenosine (5 x 10(-6)-10(-3) M) also caused relaxation of the smooth muscle cells and hyperpolarization of the cell membrane. Theophylline (5 x 10(-6)-10(-3) M) did not antagonize these effects; in the presence of theophylline (5 x 10(-5)-10(-3) M) additional relaxations produced by ATP and adenosine were limited in view of the muscle tone. These results indicate that theophylline does not inhibit either the effect of the non-adrenergic inhibitory transmitter on the smooth muscle cells of the guinea-pig stomach or the actions of ATP and adenosine. This suggests that the existence of theophylline-sensitive adenosine receptors in the stomach-muscle cell membrane is unlikely and that theophylline is not the drug of choice to support the purinergic nerve hypothesis.