ABSTRACT
Na+,K+-ATPase and Mg2+-ATPase activities were determined in the synaptic plasma membranes from hippocampus of rats subjected to chronic and acute proline administration. Na+,K+-ATPase activity was significantly reduced in chronic and acute treatment by 33% and 40%, respectively. Mg2+-ATPase activity was not altered by any treatment. In another set of experiments, synaptic plasma membranes were prepared from hippocampus and incubated with proline or glutamate at final concentrations ranging from 0.2 to 2.0 mM. Na+,K+-ATPase, but not Mg2+-ATPase was inhibited (30%) by the two amino acids. In addition, competition between proline and glutamate for the enzyme activity was observed, suggesting a common binding site for these amino acids. Considering that Na+,K+-ATPase activity is critical for normal brain function, the results of the present study showing a marked inhibition of this enzyme by proline may be associated with the neurological dysfunction found in patients affected by type II hyperprolinemia.
Subject(s)
Hippocampus/enzymology , Proline/pharmacology , Sodium-Potassium-Exchanging ATPase/antagonists & inhibitors , Animals , Ca(2+) Mg(2+)-ATPase/antagonists & inhibitors , Ca(2+) Mg(2+)-ATPase/metabolism , Drug Interactions , Glutamic Acid/pharmacology , In Vitro Techniques , Kinetics , Proline/administration & dosage , Rats , Rats, Wistar , Sodium-Potassium-Exchanging ATPase/metabolism , Synaptic Membranes/enzymology , Time FactorsABSTRACT
Na+, K+-ATPase activity was measured in synaptic plasma membrane from cerebral cortex of Wistar rats subjected to experimental phenylketonuria, i.e., chemical hyperphenylalaninemia induced by subcutaneous administration of 5.2 micromol phenylalanine / g body weight (twice a day) plus 0.9 micromol p-chlorophenylalanine / g body weight (once a day). The treatment was performed from the 6th to the 14th postpartum day and rats were killed 12 h after the last injection. Synaptic plasma membrane from cerebral cortex was prepared by a discontinuous density sucrose gradient for Na+, K+-ATPase activity determination. The results showed that the enzyme activity was decreased by 30% in animals subjected to experimental phenylketonuria when compared to control. The in vitro effects of the drugs on Na+, K+-ATPase activity were also investigated. Phenylalanine and p-chlorophenylalanine inhibited the enzyme activity and this inhibition was reversed by alanine. In addition, competition between phenylalanine and p-chlorophenylalanine for binding to the enzyme was observed, suggesting a common binding site for these substances. Our results suggest that reduction of Na+, K+-ATPase activity may be one of the mechanisms related to the brain dysfunction observed in human PKU.
