Barium removes the ouabain-induced increase in the rod response to light

The mass receptor potential of the excised, superfused retina of the bullfrog was isolated with aspartate. Rods were selectively stimulated by using very dim flashes of light. In the presence of 0.1 mM ouabain, the amplitude of the receptor response was found first to increase transiently and, subsequently, to decrease progressively. The ouabain-induced transient increase in receptor response was completely eliminated by 0.4 mM barium chloride. However, barium did not affect the rate at which the response decayed in the presence of ouabain. The ability of barium to remove the ouabain-induced transient increase in the amplitude of the receptor response is discussed in terms of reducing the coupling ratio of the postulated electrogenic sodium-potassium pump of rods.