Properties of contractions induced by ouabain and K+-free solution in guinea pig taenia coli.

The properties of contractions induced by ouabain and by K depletion were studied in comparison with those induced by other stimulants in guinea pig taenia coli. Ouabain 7.5 X 10(-6) M and K depletion produced biphasic contractions with similar time courses. Both contractions were slightly inhibited by low (0.25 mM) and high (7.5 mM) Ca concentrations, while the high K contraction was strongly inhibited by low Ca and potentiated by high Ca. Contractions induced by ouabain and K depletion were highly sensitive to lowering of the temperature and abolished at 15 degrees C, although contractions induced by carbachol 1.1 X 10(-7) M and histamine 5 X 10(-7) M were still observed below 15 degrees C. In Cl deficient solution substituted by SO4 or propionate, contractions induced by ouabain and K depletion were potentiated, while contractions induced by high K, carbachol and histamine were suppressed. These results indicate a striking similarity between contractions induced by ouabain and K depletion suggesting a common mechanism for both contractions.