Synaptosomal Na+,K+-ATPase as a membrane probe in studying the in vivo action of morphine.

The activity of membrane-bound Na+,K+-ATPase was used as a metabolic probe to study the effects of morphine in vivo in rat brain synaptosomes. Arrhenius plots were generated to study an induced perturbation within the membrane. In acute studies 0.5-h postmorphine, the drug was without effect on the basal activity of the enzyme. With dopamine-stimulated Na+,K+-ATPase morphine decreased the apparent transition temperature and specific activity of the enzyme while there was a slight stimulation in its activation energy. An increase in these parameters was observed in samples taken from animals withdrawn from the drug for 48 h. These results strongly suggest the possible involvement of the membrane phospholipids as transducer which mediates the observed biphasic effect of the drug on enzyme activity.