Electrical activity of human colonic smooth muscle in vitro.

1. Extracellular and intracellular recordings were made of the electrical activity of isolated strips of human colonic smooth muscle, cut from sixty surgical specimens. 2. Strips of taenia were spontaneously active. The myogenic activity consisted in half the strips of intermittent periods of regular spike activity (frequency 22 +/- 5 (S.D.) c/min) accompanied by tetanic contractions; in the other half of the strips activity was continuous. In half the specimens, slow potentials were recorded between periods of spike activity. Slow potentials were not accompanied by contractions. 3. Spikes in taenia were abolished by verapamil. Spikes disappeared in low Ca and low Na solutions, but in low Na solution spikes could be stimulated by 15 mM-KCl. 4. ACh and physotigmine produced tetanic contractions in taenia. 5. Circular muscle was not spontaneously active within 1 h of incubation in the water bath, possibly due to inhibition by prostaglandins. 6. Circular muscle responded to ACh with irregular bursts of spikes associated with discrete contractions. Similar activity was seen after inhibition of prostaglandin synthesis with indomethacin. After treatment with tetrodotoxin, ACh produced regular spikes and tetanic contractions in circular muscle. 7. The possible relationships of these results to the myoelectrical activity of the human colon in vivo are discussed.