Organization of electrical activity in the canine pyloric canal

1. The electrical activity of the canine gastroduodenal junction was investigated using cross-sectional muscle preparations and intracellular recording techniques. 2. Spontaneous electrical slow waves were recorded from antral and pyloric cells but not from duodenal cells adjacent to the pyloric region. Slow waves were generated in the antrum and propagated to the pyloric region via the circular layer. Pyloric slow waves consisted of an upstroke phase, a plateau phase and oscillations superimposed upon the plateau, whereas antral slow waves had smooth plateau potentials. 3. Within the pylorus slow waves decayed in amplitude with distance from the myenteric border of the circular muscle; the majority of pyloric circular cells were normally electrically quiescent. 4. The longitudinal muscle in the pylorus was electrically coupled and paced by the circular muscle. In longitudinal cells slow waves were usually of long duration with multiple spikes superimposed upon the plateau phase. 5. Nifedipine (10(-8) to 10(-5) M) decreased slow waves amplitude and duration. Tetraethylammonium ions (TEA; 10 mM) increased the duration of slow waves, caused spiking activity during the plateau phase and also elicited spiking in the quiescent regions. 6. The results suggest that gastric slow waves pace the myenteric portion of the circular muscle layer and the longitudinal layer of the pylorus, but do not traverse the gastroduodenal junction, nor pace the majority of cells within the circular muscle of the pylorus. Other excitatory mechanisms are necessary to activate these regions and to co-ordinate their motility with gastric motility.