In vitro inhibition of Na+,K(+)-ATPase activity from rat cerebral cortex by guanidino compounds accumulating in hyperargininemia.

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.