Effect of Cd2+ and Hg2+ on the activity of Na+/K+-ATPase and Mg2+-ATPase adsorbed on polystyrene microtiter plates

In the present study a polystyrene microtiter plate was tested as a support material for synaptic plasma membrane (SPM) immobilization by adsorption. The adsorption was carried out by an 18-h incubation at +4degreesC of SPM with a polystyrene matrix, at pH 7.4. Evaluation of the efficiency of the applied immobilization method revealed that 10% protein fraction of initially applied SPM was bound to the support and that two SPM enzymes, Na+/K+-ATPase and Mg2+-ATPase, retained 70-80% activity after the adsorption. In addition, adsorption stabilizes Na+/K+-ATPase and Mg2+-ATPase, since the activities are substantial 3 weeks after the adsorption. Parallel kinetic analysis showed that adsorption does not alter significantly the kinetic properties of Na+/K+-ATPase and Mg2+-ATPase and their sensitivity to and mechanism of Cd2+- or Hg2+- induced inhibition. The only exception is the "high affinity" Mg2+-ATPase moiety, whose affinity for ATP and sensitivity toward Cd2+ were increased by the adsorption. The results show that such system may be used as a practical and comfortable model for the in vitro toxicological investigations. (C) 2001 Elsevier Science.