Protein synthesis in brain slices. Effects of electrical stimulation and acidic amino acids.

Protein synthesis in brain slices was followed by the incorporation of 14C-amino acid, mostly r4C-valine; it remained steady for at least 4 hours at 37”. When applied for 15 min or longer, electrical stimulation of slices, by use of alternating line current reduced to 0.5 to 3 volts, inhibited protein synthesis increasingly, the inhibition reaching a plateau at 1.5 volts. For comparison, the paired slice technique was used. When stimulation was in the presence of uniformly labeled i4C-glucose, only slight inhibition of 14C! incorporation into proteins was found. However, electrical stimulation also increases the conversion of glucose to amino acids. Therefore, the pool of 14C-labeled amino acids increases with stimulation. If this is taken into account, the degree of inhibition of protein synthesis due to electrical stimulation becomes equal whether the amino acid is internally produced from glucose or is added to the suspending fluid. Acidic amino acids that have excitatory effect on nerves in uiuo were found to inhibit protein synthesis in brain slices in the following order of decreasing percentage inhibition: DL-homocysteate (47%), L-glutamate (34%), D-aspartate (35%), and DL-or-aminoadipate (17%). Exposure was for 60 min at 37’. The order is approximately parallel to their excitatory potency on nerves. In both electrical and chemical stimulation, the inhibition of protein synthesis was poorly reversible or irreversible. Analogous effects of electrical stimulation or acidic amino acids were not found with kidney slices. Amino acid permeation in brain slices was unaffected by electrical or chemical stimulation.