Effects of L-phenylalanine on acetylcholinesterase, (Na+,K+)-ATPase and Mg2+-ATPase activities in adult rat whole brain and frontal cortex

The effect of different L-phenylalanine (Phe) concentrations (0.12-12.1 mM) on acetylcholinesterase (AChE), (Na+,K+)-ATPase and Mg2+-ATPase activities was investigated in homogenates of adult rat whole brain and frontal corte x at 37 degreesC. AChE, (Na+,K+)-ATPase and Mg2+-ATPase activities were det ermined after preincubation with Phe. AChE activity in both tissues showed a decrease up to 18% (p<0.01) with Phe. Whole brain Na+,K+-ATPase was stimu lated by 30-35% (p<0.01) with high Phe concentrations, while frontal cortex Na+,K+-ATPase was stimulated by 50-55% (p<0.001). Mg2+-ATPase activity was increased only in frontal cortex with high Phe concentrations. It is sugge sted that: a) The inhibitory effect of Phe on brain AChE is not influenced by developmental factors, while the stimulation of Phe on brain Na+,K+-ATPa se is indeed affected; b) The stimulatory effect of Phe on rat whole brain Na+,K+-ATPase is decreased with age: c) Na+,K+-ATPase is selectively more s timulated by high Phe concentrations in frontal cortex than in whole brain homogenate: d) High (toxic) Phe concentrations can affect Mg2+-ATPase activ ity in frontal cortex, but not in whole brain, thus modulating the amount o f intracellular Mg2+.