Membrane changes induced by high electric fields. Evidence for sulfhydryl group involvement

The dielectric breakdown of human erythrocyte membranes under high electric fields (> 0.8 kv/cm) was not affected by enzymatic pretreatment with neuraminidase or pronase by chemical modification of exposed amino groups (by means of trinitrobenzene sulfonate) or readily exposed thiol groups (by N-ethylmaleimide). The organic mercurials, on the other hand, which are known to react with the hydrophobic sulfhydryl groups that affect the selective cationic permeability of the membrane, exhibited remarkable inhibitory action: p-chloromercuribenzene sulfonate and p-chloromercuribenzoate at concentrations of 10^-4 M attenuated the decrease in electrical size at high electric fields (10 kv/cm) by about 40%, with the latter, the more hydrophobic of the two, somewhat more effective. This inhibition was completely neutralized by adding an excess of free sulfhydryl groups (10^-3 M dithioerythritol) to the incubation medium. A quantitative analysis is presented of the electrical size of a cell as a function of the fraction of its surface area that is porous (conducting). The calculations show that it is sufficient for around 0.05% of the total surface area of the erythrocyte to become permeable in order for the electrical size to drop to the levels observed under high fields. A model of dielectric breakdown is proposed in which the instability induced in the lipid bilayer by the electric field is transduced into changes in membrane permeability by hydrophobic interaction, with the sulfhydryl groups controlling the cationic channels on the erythrocyte surface.