Transmission from intramural excitatory nerves to the smooth muscle cells of the guinea-pig taenia coli.

1. A study has been made of transmission from intramural excitatory nerves to the smooth muscle cells of the guinea-pig taenia coli.2. Only ten cells out of eighty gave depolarizing (i.e. excitatory junction potentials, E.J.P.S) on stimulating the intramural nerves, the remaining cells gave hyperpolarizing responses (i.e. inhibitory junction potentials, I.J.P.S). E.J.P.S were recorded in cells which were less than 1 mm away from cells which gave I.J.P.S.3. In some cells stimulation of the intramural nerves with single pulses of maximal strength gave E.J.P.S of about 20 mV amplitude after a latency of 100-200 msec. In quiescent cells these E.J.P.S gave rise to action potentials. Repetitive stimulation above 1 c/s depolarized the membrane for less than about 1 sec, and during the remainder of the stimulation no action potentials fired, even in spontaneous cells.4. In some cells stimulation of the intramural nerves gave an I.J.P. The largest sized I.J.P.S were generally only about half the size of the I.J.P.S recorded in atropinized preparations. The decreased amplitude of the I.J.P.S enabled rebound action potentials to be fired by successive I.J.P.S when the intramural nerves were stimulated at about 1 c/s. At higher frequencies all spontaneous activity was suppressed.5. The effect of neostigmine (10(-9)-10(-7) g/ml.) on the transmission was studied. There was no detectable increase in the number of cells giving E.J.P. responses in the presence of neostigmine.6. The electrophysiological characteristics of intramural excitatory and inhibitory nerve transmission are discussed.