Propagation and entrainment of slow waves in cat small intestine

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Abstract
Slow-wave propagation was established in everted mucosa-free preparations of intestinal muscle. Following the establishment of a control propagation direction and phase relationship between wave forms at 4 recording locations, rings of circular muscle were removed leaving only longitudinal muscle bridging intact segments. Slow waves, recorded extracellularly, remained phase-locked across bridges of longitudinal muscle less than 5 mm wide although the lag between wave forms at recording sites to either side of the ring was sometimes greater than control. Microelectrode recordings made at various locations on the bridging longitudinal muscle showed slow-wave amplitude to be greater near the driving than the following side or at intermediate locations. Azimuthal recordings from the longitudinal bridge midline demonstrated appreciable variations in slow-wave amplitude. Propagation was also examined with the preparation mounted in the normal configuration (longitudinal muscle out). Slow waves remain phase-locked after circumferential transection of the longitudinal muscle, although sometimes changes in propagation velocity occurred. Tetraethylammonium greatly increased the distance over which electrical activity was conducted in isolated circular muscle. Slow-wave activity could be entrained to pulse stimuli whose repetition rate was higher than the spontaneous frequency in strips of both isolated longitudinal and mixed muscle. Neither muscle layer is by itself necessary for the maintenance of propagation over short distances. The circular muscle layer is important in supplying excitatory current necessary for normal propagation.

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