ABSTRACT
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.
Subject(s)
Cerebral Cortex/drug effects , Fenclonine/pharmacology , Neurons/drug effects , Phenylalanine/pharmacology , Phenylketonurias/enzymology , Sodium-Potassium-Exchanging ATPase/drug effects , Synaptic Membranes/drug effects , Animals , Animals, Newborn , Body Weight/drug effects , Body Weight/physiology , Ca(2+) Mg(2+)-ATPase/drug effects , Ca(2+) Mg(2+)-ATPase/metabolism , Cerebral Cortex/enzymology , Cerebral Cortex/ultrastructure , Nerve Tissue Proteins/metabolism , Neurons/enzymology , Neurons/ultrastructure , Organ Size/drug effects , Organ Size/physiology , Pharmacokinetics , Phenylketonurias/physiopathology , Rats , Rats, Wistar , Sodium-Potassium-Exchanging ATPase/metabolism , Subcellular Fractions/drug effects , Subcellular Fractions/metabolism , Synaptic Membranes/enzymology , Synaptic Membranes/ultrastructureABSTRACT
Hyperargininemia is a metabolic disorder biochemically characterized by tissue accumulation of arginine (Arg) and other guanidino compounds (GC). Convulsions, lethargy and psychomotor delay are predominant clinical features of this disease. Considering that some GC are epileptogenic and cause a decrease in membrane fluidity and that Na+,K(+)-ATPase, a membrane-bound enzyme, is essential for cellular excitability and is decreased in experimental and human epilepsy, in the present study we determined the in vitro effects of Arg, N-acetylarginine (NAA), argininic acid (AA) and homoarginine (HA) on the activity of Na+,K(+)-ATPase in the synaptic plasma membrane from cerebral cortex of young rats in the hope to identify a possible mechanism for the brain damage in hyperargininemia. The results showed that all GC tested, except Arg, significantly inhibited Na+,K(+)-ATPase activity at concentrations similar to those observed in plasma and CSF of patients with hyperargininemia. In addition, competition between NAA, AA and HA for the binding to the enzyme was observed, suggesting a common binding site for the GC. It is therefore possible that the inhibitory effect of GC on Na+,K(+)-ATPase may be related to the brain dysfunction observed in hyperargininemia.
