Na and K Fluxes in Nitella clavata.

Na and K influxes and effluxes, membrane potentials, and cell ion concentrations of Nitella clavata were measured as functions of external NaCl concentrations and time. It appears necessary to conclude that active K transport into the cells as well as active Na extrusion is present, although the latter is of small magnitude and possibly is explicable as exchange-diffusion. An attempt has been made to account for the capacity of the cells to discriminate between K and Na ions and yet have fairly independent passive ion movements. This is done by proposing a model in which the permeation areas are "slit-pores" rather than cylindrical pores. The slit-pores would permit rather independent movements of ions within them so long as the pores do not tend to become saturated from both or either side. In the latter case one way movement results. The experimental results are in fair agreement with this suggested model.