Human Colonic Smooth Muscle Research Articles

Electrical basis of excitation and inhibition of human colonic smooth muscle

Excitation and inhibition of electrical activities of the musculature of the human colon and the consequent changes in motor activities were studied in vitro. The mechanisms of excitation and inhibition were very different from those of the small intestine and colons from animal models. Carbachol increased spiking activity and the frequency of bursts of electrical oscillations in longitudinal muscle. Each longitudinal muscle contraction was related to a burst of electrical oscillations. Carbachol induced one of three patterns of activity in circular muscle: (a) continuous electrical oscillatory activity (14–24 cpm) with spikes, associated with tonic contraction; (b) bursts of such electrical activity, associated with broad phasic contractions; or (c) prolonged membrane potential depolarizations (frequency 1–3 cpm) with superimposed intense spiking activity, associated with phasic contractions. Isoproterenol inhibited all electrical and mechanical activities in both muscle layers. These results may provide a better understanding of (a) the origins of the variable patterns of electrical and motor activities and (b) the relationship between electrical and mechanical activities of the human colon musculature.

Human colonic smooth muscle: electrical and contractile activity in vitro.

Extracellular electrical and contractile activities were recorded in vitro from strips of human colonic smooth muscle obtained at the time of surgery. Serosal electrical activity of longitudinally oriented strips from the taenia and intertaenial region was characterised by continuous oscillation at a frequency of 28 +/- 1/min. Contractions were marked electrically by a series of oscillations upon which spikes were superimposed. The electrical activity recorded from the submucosal surface of circularly oriented strips exhibited oscillations at 24 +/- 4/min, a frequency significantly lower (p less than 0.001) than that recorded from the serosal surface of similar preparations. The contractile force and frequency was dependent upon the part of the colon from which the strip originated; the most powerful contractions were recorded from strips of sigmoid colon. The contractile frequency of circularly oriented strips from the right colon was 6.3 +/- 0.6/min, significantly higher (p less than 0.001) than that of strips from the left colon (3.4 +/- 0.3/min). Stretching these strips caused an increase in contractile frequency to that of the electrical oscillation.

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.