Evidence for differential function of neuronal and glial cells in protein metabolism and amino acid transport.

Amino acid incorporation in neuronal and glial cells has been investigated in several laboratories employing bulk-separation techniques to obtain cell-enriched fractions. The relative rates of incorporation into the proteins of both cell types vary substantially with the method of isotope administration. Through the use of single-pulse perfusions with a duration of 30-40 sec the early time course of labeling has been studied. The difference between neuronal and glial cells with respect to indicating cell interactions will be discussed. The in vitro amino acid incorporation has been measured in neurons and glia after slice incubation. In material from animals developing experimental allergic encephalitis the rate of 3H-leucine incorporation more than doubles in the unfractionated brain. Glial cells increased their rate of incorporation by approximately 400% under the same conditions. The involvement of specific proteins in the cells and organelles has been studied by gel electrophoresis. The high uptake capacity of glial cells for certain amino acids with possible transmitter function has been further characterized. The release of these substances is measured in a superfusion system where beds of cells, preloaded with the labeled substance, are used. High potassium pulses stimulate release of, for example, GABA in both neuronal and glial cells.