Comparison between acute and chronic effects of ammonia on branched-chain amino acid oxidation and incorporation into protein in primary cultures of astrocytes and of neurons.

A comparison was made of acute and chronic effects of ammonia on production of 14CO2 from the [U-14C] labeled branched-chain amino acids (BCAA) leucine, isoleucine, and valine as well as from [1-14C] leucine, and on the incorporation of radioactivity from these amino acids into a perchloric-acid-precipitable protein fraction in astrocytes and neurons in primary cultures. Acute exposure of astrocytes to 3mM ammonium chloride suppressed 14CO2 production from [U-14C] BCAA and especially from [1-14C] leucine. This inhibitory effect was abolished or even reversed [( U-14C] leucine) after chronic exposure to ammonia. Analogously, incorporation of radioactivity into the protein fraction was inhibited after acute exposure but not after chronic exposure of astrocytes to ammonia. The total protein content per culture was increased after chronic exposure. In neurons, production of 14CO2 and incorporation of 14C into proteins were less affected than in astrocytes. These results are discussed in relation to the ability of the two cell types to synthesize glutamine.