Energy-linked Potassium Influx as Related to Cell Potential in Corn Roots

Cell potentials and K(+) ((86)Rb) influx were determined for corn roots over a wide range of external K(+) activity (K degrees ) under control, anoxic, and uncoupled conditions. The data were analyzed using Goldman theory for the contribution of passive influx to total influx. For anoxic and uncoupled roots the K(+) influx shows the functional relationship with K degrees predicted with constant passive permeability, although K(+) permeability in uncoupled roots is about twice that of anoxic roots. In control roots the equation fails to describe K(+) influx at low K degrees , but does so at high K degrees , with a gradual transition over the region where the electrical potential becomes equal to the equilibrium potential for K(+) (psi = E(K)). In the low K degrees range, where net K(+) influx is energetically uphill, participation of an energy-linked K(+) carrier is indicated. In the high K degrees range, K(+) influx becomes passive down the electrical gradient established by the cell potential. Since the cell potential includes a substantial electrogenic component, anoxia or uncoupling reduces passive influx.