Effect of Sulfhydryl Reagents on the Biophysical Properties of the Plasmalemma of Chara corallina

The administration of the sulfhydryl reagent N-ethyl-maleimide (NEM) to internodal cells of Chara corallina caused alterations in the biophysical properties of the plasmalemma, as measured with electrophysiological and radioactive tracer techniques. The membrane potential depolarized to, or near, the calculated Nernst potential for potassium (E(K)) after 30 seconds' exposure to 0.1 millimolar NEM. During this time, the ATP level did not decrease below the control value, and the specific membrane resistance did not increase; only upon further exposure to NEM did the resistance approach the value observed in the dark. In the depolarized state, the membrane potential responded to changes in the external potassium concentration in the manner of a K(+)-electrode, but it retained it's relative insensitivity to external sodium.THESE RESULTS ARE INTERPRETED IN THE FOLLOWING MANNER: NEM causes a) an increase in the membrane permeability to K(+) (i.e. an increase in K(+) conductance); and b) perturbation of the electrogenic transport system(s) of the plasma membrane. The latter effect is manifested in a manner that is not consistent with an inhibition of ATP catalysis by a voltage-dependent ATPase possessing conductance. The nonpermeant sulfhydryl modifier, p-chloromercuribenzenesulfonic acid, appeared to affect membrane properties in a similar, but reversible, way.