Two types of 'slow waves' in intestinal smooth muscle of cat.

1. Smooth muscle from cat small intestine shows two types of spontaneous slow electrical waves in the frequency range of 10-15 min-1. One type of slow wave is a ouabain-sensitive, atropine-insensitive spontaneous oscillation. The other type of wave can be induced by acetylcholine (ACh), is blocked by atropine, and is not blocked by ouabain. 2. Ouabain-sensitive slow waves rise directly from the baseline, are near sinusoidal and may or may not have spikes. ACh-induced waves have pre-potentials, are usually topped by spikes and show after-hyperpolarization. 3. The two types of rhythmic wave differ in ionic and metabolic requirements and drug sensitivity. Ouabain-sensitive waves occur only in intestinal muscle attached to a boundary layer containing interstitial cells; ACh-induced waves can occur in strips of muscle lacking boundary cells. 4. Na+ pump inhibitors ouabain, cold and K+-free solution, reduce amplitude but not frequency of ouabain-sensitive slow waves. 5. The ACh-induced waves require higher extracellular concentrations of Na+ and Ca2+ and can occur in preparations in Li+-Krebs solution; the ouabain-sensitive rhythm persists in lower concentrations of Na+ and Ca2+ and is not supported by Li+. The ouabain-sensitive waves are more sensitive to cyanide and less sensitive to cooling than the ACh-induced waves. 6. Guinea-pig intestine shows only one type of rhythmic wave, which is atropine sensitive and resembles in shape the ACh-induced wave of other species. Ouabain increases the frequency of the guinea-pig rhythm. 7. It is concluded that intestinal muscle of most mammals, but not of guinea-pig, is capable of two types of slow electrical rhythms.