Anisotropic propagation in the small intestine

Measuring propagation anisotropy may help in determining the tissue layers involved in the propagation of electrical impulses in the intestine. We used 240 extracellular electrograms recorded from the isolated feline duodenum. The conduction velocities of slow waves and of individual spikes were measured from their site of origin into all directions. Both slow waves and spikes propagate anisotropically in the small intestine but in different directions and to a different degree. Slow waves propagated anisotropically faster in the circumferential (1.7 ± 0.8 cm s^-1) than in the axial direction (1.3 ± 0.5 cm s^-1; P < 0.001). Spikes, on the other hand, propagated faster in the longitudinal direction (7.8 ± 4.5 cm s^-1) than in the circumferential direction (3.3 ± 4.3 cm s^-1; P < 0.001). Furthermore, the average conduction velocity of spikes (6.3 ± 4.5 cm s^-1) was significantly higher than that of slow waves (1.5 ± 1.1 cm s^-1; P < 0.001). The anisotropic propagation of spikes supports the argument that these propagate in the longitudinal muscle layer. The anisotropic propagation of slow waves may be the result of the interaction between the myenteric layer of interstitial cells of Cajal and their electrotonic connection to both the longitudinal and the circular muscle layer.