Inhibitory junction potentials of the guinea-pig duodenum in the treatment with catecholamines

The inhibitory junction potentials (IJPs) in response to single and repetitive stimulation were recorded from the smooth muscle cells of the guinea-pig duodenum intracellularly. In adrenaline and noradrenaline (10(-8)-10(-5) g/ml), the IJP could be evoked in spite of a hyperpolarization of the cell membrane. The amplitude of the IJP was slightly changed in these agents but not abolished. Similar results were obtained in isoprenaline (10(-5) g/ml) and phenylephrine (10(-5) g/ml). The IJPs evoked by single and repetitive stimulation were not blocked by phentolamine (10(-7) g/ml) and propranolol (10(-5) g/ml). In propranolol (10(-7)-10(-5)/g/ml), the membrane was depolarized and the amplitude and the rate of hyperpolarization in the IJP were decreased. The membrane potential was decreased and the amplitude of the IJP was slightly increased in the presence of guanethidine (10(-5) g/ml). The amplitude of the IJP was increased with increasing the concentration of tyramine (10(-6)-10(-5) g/ml). These results suggest that the transmitter released from the intramural inhibitory nerve in the duodenum is nonadrenergic and this type of inhibition seems to be independent from adrenergic inhibition.