Effects of sodium, potassium and calcium ions on the slow wave in the circular muscle of the guinea-pig stomach.

1. The contribution of Na, K and Ca ions to the generation of slow waves in the circular muscle of the guinea-pig stomach was studied.2. The slow waves had a lower, potential-independent (first) and an upper, potential-dependent (second) component. Reduction of the external Na prolonged the first component, but complete removal of Na depolarized the membrane and caused deterioration of the slow wave.3. Readmission of Na (5-10 mM) restored the slow wave; this action was not abolished by ouabain.4. Removal of K depolarized the membrane and slightly reduced the amplitude and duration of the slow waves. Readmission of K hyperpolarized the membrane and increased the amplitude and duration of the slow waves, particularly of the first component. Ouabain blocked the effects on the membrane potential, but not the effects on the slow waves.5. An increase in extracellular Ca prolonged the first component and reduced the frequency. Removal of extracellular Ca abolished the slow wave activity. Excess Ca enhanced, and low Ca reduced the effects of altering the concentrations of external K.6. It is concluded that the ouabain-sensitive Na-K pump may not be directly involved in generating slow waves, but that some other metabolic process is involved, which is regulated to a large extent by Ca, and possibly also by Na and K.