Effect of calcium chelation by L-phenylalanine on (Na + + K +)-stimulated ATPase of chick brain microsomes

Abstract

Previous work from this laboratory has revealed that chicks showed a reversible narcosis when injected with 1.62 nmole of L-phenylalanine [ 1 ] . After 4 hr, the brain phenylalanine level was as high as 3.8 pmole/g tissue [2]. It has been shown that some amino acids are chelators of divalent cations [3-61. Since membrane-bound Ca2+ is essential for the maintenance of cellular and axonal membrane excitability and low Ca2+ leads to depolarization, spontaneous electrical discharges and eventually suppression of membrane excitability [7151, it was of interest to test the hypothesis that high concentrations of L-phenylalanine (up to 5 mM) might compete for Ca2+ and displace it from the membrane surface. This displacement, in vim, would lead to reduction (and ultimate blockage) of the action potential. This communication reports studies of the effect of L-phenylalanine on membrane-bound (Na+ + K+)ATPase as compared with the effects of strong chelators such as EDTA and EGTA on the same system.