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

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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.

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