Spatial and temporal coupling between slow waves and pendular contractions.

In contrast to the mechanisms of segmental and peristaltic contractions in the small intestine, not much is known about the mechanism of pendular contractions. High-resolution electrical and mechanical recordings were performed from isolated segments of the rabbit ileum during pendular contractions. The electrical activities were recorded with 32 extracellular electrodes while motility was assessed simultaneously by video tracking the displacements of 20-40 serosal markers. The electrical activities consisted of slow waves, followed by spikes, that propagated in either the aboral or oral direction. The mechanical activity always followed the initial electrical activity, describing a contraction phase in one direction followed by a relaxation phase in the opposite direction. Pendular displacements were always in rhythm with the slow wave, whereas the direction of the displacements was dictated by the origin of the slow wave. If the slow wave propagated aborally, then the pendular displacement occurred in the oral direction, whereas if the slow wave propagated in the oral direction, then the displacement occurred in the aboral direction. In the case of more complex propagation patterns, such as in the area of pacemaking or collision, direction of displacements remained always opposite to the direction of the slow wave. In summary, the direction and pattern of propagation of the slow wave determine the rhythm and the direction of the pendular motility. The well-known variability in pendular movements is caused by the variability in the propagation of the underlying slow wave.