The action of ouabain on the smooth muscle cells of the guinea-pig's taenia coli.

1. The action of 10(-6) g/ml. of ouabain on the membrane potential, membrane activity, tension development and the ion content of the smooth muscle of the guinea-pig's taenia coli has been investigated.2. This ouabain concentration produced a depolarization of the membrane, accompanied by an initial increase of the spike frequency and later a depolarization block. Removal of the ouabain produced a sudden and pronounced hyperpolarization leading to a block of spike discharge.3. Reduction of the external sodium concentration, or an increase of the external calcium concentration, or exposure to 10(-7) g/ml. adrenaline repolarized the cell membrane in the presence of ouabain.4. Ouabain decreased the tension development of the taenia coli.5. Ouabain decreased the intracellular potassium and chloride and increased the intracellular sodium concentration. However, the corresponding changes of the equilibrium potentials were not sufficient to explain the changes of the membrane potential.6. A possible explanation for the action of ouabain is presented suggesting that the drug may decrease the calcium binding properties of the cell membrane.