In vitro electrical activity in human colon.

Extracellular electrical activity was measured in vitro in 28 specimens of human colon taken at the time of operation. The mucosa was removed, and the muscle strips were mounted in an organ bath irrigated with oxygenated Krebs. Records were made from 3-7 silver/silver chloride electrodes placed directly on the circular muscle, for periods of 15-30 min. Data were stored on magnetic tape, digitized, analyzed by the fast Fourier transform method and plotted in three-dimensional form (signal power vs. frequency vs. time). Some plots showed a single frequency peak in the range 2-9 cpm, which was present throughout the study. However, multiple peaks were frequently seen and were of two types: (a) peaks of two or three closely related frequencies in the 2-9 cpm range, which divided and fused during the recording time. The power of the fused peak was greater than that of the components. And (b) peaks at frequencies which were integer multiples of the fundamental frequency; we interpret these to be the second and third harmonics of the fundamental frequency. When the fundamental frequency peak developed into several components, similar components also appeared at their individual harmonic frequencies, i.e., the second harmonic components were separated by twice the interval between the fundamental components. We conclude that only one fundamental frequency of electrical activity exists in any one site in human colon. Multiple frequencies are due either to the simultaneous recording from two or more poorly coupled electrical oscillators or to harmonics of the fundamental frequency.