Generation of slow waves in the antral region of guinea-pig stomach--a stochastic process.

1. Slow waves were recorded from the circular muscle layer of the antral region of guinea-pig stomach. Slow waves were abolished by 2APB, an inhibitor of IP(3)-induced Ca2+ release. 2. When the rate of generation of slow waves was monitored it was found to vary from cycle to cycle around a mean value. The variation persisted after abolishing neuronal activity with tetrodotoxin. 3. When simultaneous recordings were made from interstitial cells in the myenteric region (ICC(MY)) and smooth muscle cells of the circular layer, variations in the rate of generation of slow waves were found to be linked with variations in the rate of generation of driving potentials by ICC(MY). 4. A preparation was devised which consisted of the longitudinal muscle layer and ICC(MY). In this preparation ICC(MY) and smooth muscle cells lying in the longitudinal muscle layer generated driving potentials and follower potentials, synchronously. 5. Driving potentials had two components, a rapid primary component that was followed by a prolonged plateau component. Caffeine (3 mM) abolished the plateau component; conversely reducing the external concentration of calcium ions [Ca2+](o) mainly affected the primary component. 6. Analysis of the variations in the rate of generation of driving potentials indicated that this arose because both the duration of individual driving potentials and the interval between successive driving potentials varied. 7. It is suggested that the initiation of pacemaker activity in a network of ICC(MY) is a stochastic process, with the probability of initiating a driving potential slowly increasing, after a delay, from a low to a higher value following the previous driving potential.