Evidence in favor of carbon dioxide rather than H+ ion as a stimulant of the sodium efflux in barnacle muscle fibers

Acidification of the bathing medium in the absence of external bicarbonate ions was without effect on the Na efflux. By contrast, acidification in the presence of different concentrations of HCO 3 − led to stimulation of the Na efflux. Measurements of the pCO 2 indicated that stimulation of the pump always took place when the pCO 2 reached approximately 40 mm Hg.