Effect of aldosterone on 86Rb fluxes in cultured kidney cells (A6)

This study was designed to evaluate the relative contributions of hormone induced changes in active and passive K+ transport in an epithelial cell line in continuous culture derived from toad kidney (A6) using 86Rb as a tracer for measuring unidirectional K+ fluxes. The effects of 24 h exposure to aldosterone (A) and aldosterone plus insulin (A+I) on unidirectional K+ fluxes were evaluated under short-circuited conditions and under open circuit conditions. In epithelia exposed to A, a small but significant amount of active K+ secretion was found, although it was not significantly greater than in control epithelia. The bidirectional fluxes in both A and A+I treated epithelia, under short-circuited conditions, increased by a similar amount over control values indicating an increase in apparent permeability of passive transepithelial K+ transport. Under open circuit conditions, A stimulated net K+ transport by about 5-fold over controls. The increase in K+ secretion produced by A under open circuit conditions could be explained by the combined effects of an increase in transepithelial K+ permeability and an increase in the transepithelial electrical potential difference (PD). The presence of I produced no additional effects to that of A on K+ transport under the conditions used in this study. It is concluded that the substantial increase in K+ secretion induced in A6 cells by 24 h exposure to A is primarily passive in nature. It is possible that the changes in both PD and transepithelial K+ permeability, which can account for the observed increase in K+ secretion, are secondary to the stimulation of active Na+ transport.