The effects of alternating currents on Na,K-ATPase function

Abstract

We prepared Na, K-ATPase from rabbit kidney and have studied the rate of ATP splitting when ac currents flow through the enzyme suspension via platinum electrodes/salt-impregnated agar gels. The ac signals covered an amplitude range of 1 mV–1 V (across an enzyme suspension resistance of 44 Ω) and a frequency range of 10–100,000 Hz. We found the ac decreased ATP splitting by the normal enzyme, with the maximum decrease in the range of 100–1000 Hz and at an estimated current density of about 0.5 mA/cm 2. The ac signals could also increase the enzyme activity, but only when the control activity was low. The lowered enzyme activity was achieved by natural decay of the enzyme during storage under refrigeration, by lowering the temperature, and by introducing partially effective concentrations of ouabain. The ouabain experiments showed a different quantitative dependence of the enzyme activity on the electric current, suggesting the ac was antagonizing the inhibitory effect of ouabain, probably by increasing the effective K + ion concentration. Our experiments suggest that ac stimulated ion transport in erythrocytes, may be due to AC induced ion migration in solution that perturbs ion activation of the enzyme. The observed enhancement or inhibition of the Na,K-ATPase activity probably depends upon the effects of the ionic changes relative to the optimal ion ratios for activity.