Myogenic electrical control activity in longitudinal muscle of human and dog colon

1. The myogenic electrical activities of longitudinal muscle cells of the dog and human colon were investigated using intracellular microelectrodes. 2. The resting membrane potentials of dog and human longitudinal muscle cells at the serosal side of the muscle layer were -49.4 +/- 0.9 and -44.8 +/- 1.3 mV respectively. 3. Spontaneous electrical activity consisted of electrical oscillations of 13.7 +/- 1.1 mV and 8.6 +/- 2.1 mV amplitude, and 19.8 +/- 1.0 cycles/min and 26.1 +/- 1.6 cycles/min frequency for dog and human cells respectively. 4. Spiking activity only occurred superimposed on the electrical oscillations; the mean rate of rise of spikes was approximately 150 mV/s in the dog and approximately 260 mV/s in human cells and that of the oscillations was approximately 18 mV/s in the dog and approximately 16 mV in human cells. 5. Spiking activity was abolished by calcium influx blockers and 0.01 mM-calcium Krebs solution. The amplitude of the electrical oscillations was reduced to 0.2-1.0 mV 30 min after calcium influx blockade or 30 min in 0.01 mM-calcium Krebs solution. 6. Because of the high frequency of the oscillation-spike complexes, there was summation of associated contractile events in such a way that contraction frequency corresponded to frequency of bursts of oscillations and not to the frequency of the individual oscillations. 7. The resting membrane potential of the longitudinal muscle cells at the myenteric plexus side of the layer was -44.9 +/- 1.0 mV, significantly lower than at the serosal side. 8. A gradient in membrane potential and slow-wave amplitude exists in circular muscle of dog colon, with the highest value at the mucosal side (-68.4 and 28.1 mV respectively) and the lowest at the myenteric side (-62.5 and 8.6 mV) of the muscle layer. 9. Differences between resting membrane potential and electrical activity of longitudinal and circular muscle cells of the dog colon measured at the myenteric side of both muscle layers suggests absence of electrotonic coupling between the two types of cells. 10. Similarity of resting membrane potentials of longitudinal and circular muscle of the human colon suggests possible electronic coupling. 11. Since the electrical oscillations in longitudinal muscle control occurrence of spiking activity and type of contraction, they may be called 'electrical control activity'.