Ion Transport in Hyclrodictyon africanum

The concentrations of K, Na, and CI in the cytoplasm and vacuole, the tracer fluxes of these ions into and out of the cenocyte, and the electrical potential difference between bathing solution and vacuole and cytoplasm, have been measured in Hydrodictyon africanum. If the ions were acted on solely by passive electrochemical forces, a net efflux of K and CI and a net influx of Na would be expected. Tracer fluxes indicate a net influx of K and CI and efflux of Na in the light; these net fluxes are consequently active, with an obligate link to metabolism. The effects of darkness and low tempera- ture indicate that most of the tracer K and CI influx and Na efflux are linked to metabolism, while the corresponding tracer fluxes in the direction of the free energy gradient are not. Ouabain specifically inhibits the metabolically linked portions of tracer K influx and Na efftux. Alterations in the external K concentration have similar effects on metabolically mediated K influx and Na efflux. It would appear that K influx and Na efflux are linked, at least in the light.