Effect of ATPase Inhibitors on Cell Potential and K+ Influx in Corn Roots

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Abstract
Experiments were performed to determine the effect of plasmalemma ATPase inhibitors on cell potentials (Ψ) and K+ (86Rb) influx of corn root tissue over a wide range of K+ activity. N,N′Dicyclohexylcarbodiimide (DCCD), oligomycin, and diethylstilbestrol (DES) pretreatment greatly reduced active K+ influx and depolarized Ψ at low, but not at high, K+ activity (K°). More comprehensive studies with DCCD and anoxia showed nearly complete inhibition of the active component of K+ influx over a wide range of K°, with no effect on the apparent permeability constant. DCCD had no effect on the electrogenic component of the cell potential (Ψp) above 0.2 millimolar K°. Net proton efflux was rapidly reduced 80 to 90% by DCCD. Since tissue ATP content and respiration were only slightly affected by the DCCD-pretreatment, the inhibitions of active K+ influx and Ψp at low K° can be attributed to inhibition of the plasmalemma ATPase. It is concluded that by DCCD treatment, the energy-linked electrogenic system at high K° is separated from the energy-linked K+ influx system at low K°. The results are analyzed in terms of electrical analogue models of the membrane. The presence of two, algebraically additive electrogenic components is indicated; one is better modeled as a current source (system I) and one as a voltage source (system II). No K+ stimulation of system II is required to produce the observed K° dependence of Ψp.