Comparative study of the smooth muscle layers of the rabbit duodenum.

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Abstract
Intracellular electrodes were used to compare the electrical activity of smooth muscle cells from the longitudinal and circular layers of the rabbit duodenum and their responses to stimulation of the intramural nerves. The longitudinal muscle cells had an average membrane potential of 52 mV when measured between slow waves. Spontaneous action potentials were superimposed on every slow wave. The circular muscle cells had a higher membrane potential of 64 mV although the amplitude of the slow waves was similar to that of the longitudinal muscle cells. Spontaneous action potentials were rarely observed in the circular muscle cells. Excitatory responses were recorded in 9% of the circular muscle cells. Off excitation following termination of a train of repetitive stimulation pulses was also observed. The differences in membrane potentials, spontaneous spiking activities, neural responses and the failure to demonstrate good electrotonic coupling between the muscle layers suggest that there was poor electrotonic interaction between the muscle layers. The amplitude of the slow waves of the 2 layers was nevertheless similar. Thus the validity of the hypothesis that slow waves were transmitted passively from the longitudinal layer into the circular layer through electrotonic coupling must be questioned.

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