Interaction of the 2,6-dimethoxysemiquinone and ascorbyl free radicals with Ehrlich ascites cells: a probe of cell-surface charge.

Authors:
  • RPR Pethig
    R Pethig
  • PGP R Gascoyne
    P R Gascoyne
  • JMJ A McLaughlin
    J A McLaughlin
  • ASA Szent-Györgyi
    A Szent-Györgyi
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Abstract
The rate of quenching by Ehrlich ascites cells [mouse breast carcinoma] of anionic 2,6-dimethoxy-p-semiquinone and ascorbyl free radicals is investigated as a function of cell concentration, the blocking of cell-surface SH groups by N-ethylmaleimide and the reduction of cell-surface charge by neuraminidase. The rate of quenching is proportional to cell viability and to the number of free cell-surface SH groups. The enzymatic action of neuraminidase results in an increase of the free radical quenching rate, indiating that this rate can be used as a probe of cell-surface charge. Measurements as a function of the ionic strength of the suspending electrolyte gave a value of -1.22 .mu.C .cntdot. cm-2 for the charge density at the ascites cell surface. This is equivalent to a surface membrane potential of -14 mV for a 150 mM NaCl electrolyte and is a value in good agreement with published electrophoresis data. [Attention has been given to the 2,6-dimethoxyquinone/ascorbate mixture as this combination was observed to produce the largest dynamic population of free radicals and the most effective treatment of ascites tumors in mice.].