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

Cell potentials and K+ (86Rb) influx were determined for corn roots over a wide range of external K+ activity ($\text{K}^{\text{o}}$) 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 $\text{K}^{\text{o}}$ 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 $\text{K}^{\text{o}}$, but does so at high $\text{K}^{\text{o}}$, with a gradual transition over the region where the electrical potential becomes equal to the equilibrium potential for K+ (ψ = $\text{E}_{\text{K}}$). In the low $\text{K}^{\text{o}}$ range, where net K+ influx is energetically uphill, participation of an energy-linked K+ carrier is indicated. In the high $\text{K}^{\text{o}}$ 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.