Ion Fluxes and Short-Circuit Current in Internally Perfused Cells of Valonia ventricosa

Ion transport in the giant celled marine alga, Valonia ventricosa, was studied during internal perfusion and short-circuiting of the vacuole potential. The perfusing and bathing solutions were similar to natural Valonia sap and contained the following concentrations of major ions: Na 51, K 618, and Cl 652 mM. The average short-circuit current (I(sc)) was 97 pEq/cm(2) sec (inward positive current), and the average open-circuit potential difference (PD) was 74 mv (vacuole positive to external solution). Perfused and short-circuited cells showed a small net influx of Na (2.0 pEq/cm(2) sec) and large net influxes of K (80 pEq/cm(2) sec) and Cl (50 pEq/cm(2) sec). Unidirectional K influx was proportional to I(sc), but more than one-half of the I(sc) remained unaccounted for. Both the I(sc) and PD were partly light-dependent, declining rapidly during the first 1-2 min of darkness. Ouabain (5 x 10(-4)M) had little effect on the influx of Na or K and had no effect on I(inf) or PD. Fluid was absorbed at a rate of about 93 pliter/cm(2) sec. Reversing the direction of fluid movement by adding mannitol to the outside solution had little effect on ion movements. The ionic and electrical properties of normal and perfused cells of Valonia are compared.