| Abstract: | Inhibitory junction potentials (i.j.p.s) evoked by field stimulation were recorded from the smooth muscle cells of the guinea-pig duodenum intracellularly. The membrane potential was -54.3 mV. The parameters of the i.j.p. were as follows: latency, 71 msec; time to peak, 146 msec; amplitude, 15.5 mV; rate of hyperpolarization, 107 mV/sec; and half decay time of the i.j.p., 193 msec. Met-enkephalin (10(-7)-10(-6) M) had no effect on the membrane potential and the i.j.p. The membrane potential was decreased by beta-endorphin (1.7 X 10(-7)-6.8 X 10(-7) M). Increase in the latency and the time to peak and decrease in the amplitude and the rate of hyperpolarization of the i.j.p. were observed for beta-endorphin. "Spontaneous" excitatory junction potentials (e.j.p.s) were generated by beta-endorphin. Naloxone (3.1 X 10(-6)-3.1 X 10(-4) M) hyperpolarized the membrane of the muscle cells. At high concentrations of naloxone (3.1 X 10(-4) and 3.1 X 10(-3) M), inhibition of the i.j.p. was observed. Levallorphan (2.3 X 10(-4) M) prolonged the latency and the time to peak and reduced the amplitude of the i.j.p. The membrane potential was slightly decreased by levallorphan. "Spontaneous" e.j.p.s were generated by levallorphan in a certain population of the cells. It is concluded that Met-enkephalin does not contribute to the non-adrenergic inhibitory transmission and that beta-endorphin acts as a modulator in the control mechanism of the intestinal motility. The effects of naloxone and levallorphan on the i.j.p. are discussed. |
