Nervous factors influencing the membrane activity of intestinal smooth muscle

The effects of various chemical agents on the spontaneous membrane activities and those electrically elicited in the smooth muscles of small intestine were investigated.

1. The effects of various chemicals on the spontaneously active membrane might be summarized as follows. (a) Cholinergic agents; atropine slightly hyperpolarized the membrane and reduced the amplitude of slow potential changes even in aged preparations. Prostigmine depolarized the membrane, and enhanced the amplitude and prolonged the duration of the slow potential changes. Atropine prevented the actions of prostigmine on the membrane. (b) Ba²⁺ depolarized the membrane, and enhanced the amplitude and prolonged the duration of the slow potential changes. The spike frequency was initially increased, then reduced. Atropine and tetrodotoxin partially prevented the action of Ba²⁺ on the membrane activities.

2. Effects of chemical agents on the membrane activity elicited by electrical stimulation might be summarized as follows. (a) Short pulse stimulation (0·5-1 msec) generated the spike as a direct response of the muscle cell membrane, then it was followed by slow depolarization, delayed hyperpolarization, i.e. the `inhibitory potential', and post-inhibitory rebound successively. (b) The slow depolarization and the post-inhibitory rebound were reduced in amplitude by treatment with atropine, and enhanced by treatments with prostigmine and Ba²⁺. Tetrodotoxin blocked all activities except the spike.

3. When repetitive stimulation (20 c/s) was applied to the membrane, the membrane hyperpolarized; then, after 3-5 sec, it gradually depolarized even if the stimulation was continued, and triggered spikes. The hyperpolarization always preceded depolarization. The duration and the amplitude of the delayed depolarization was proportionally increased by the increased intensity and duration of stimulation. Atropine and tetrodotoxin blocked the generation of the post-inhibitory rebound.

4. Effects of repetitive stimulation on the stored tissues were observed. The responses to repetitive stimulation of the membrane of muscles which had been stored 50 hr at 4 °C, were the same as those observed in the fresh tissue. The response of the tissue which had been stored 100 hr was the same as that observed in the fresh tissue treated with tetrodotoxin, i.e. all activities except the spikes were blocked.