Glutamate inhibits in vitro P-32 incorporation into proteins of the cytoskeletal fraction

We report a receptor-independent activity of glutamate on the cytoskeletal- associated phosphorylating system acting on NF-M and NF-L neurofilament sub units and alpha- and beta-tubulin from the cerebral cortex of 17 day-old ra ts in vitro. When slices of cerebral cortex were incubated in the presence of glutamate (0.1 and 1.0 mu M), and the cytoskeletal fraction extracted an d incubated in the presence of the same concentration of glutamate and P-32 -ATP, we observed decreased phosphorylation of cytoskeletal. Conversely, wh en tissue slices were incubated in the presence of glutamate, but which was not added in the cytoskeletal fraction, we were not able to detect any alt eration in in vitro phosphorylation. These results demonstrate a receptor-i ndependent effect of glutamate on the phosphorylating system associated wit h the Triton-insoluble fraction. We suggest that glutamate act directly or indirectly on the enzymes (kinases and phosphatases) inhibiting the in vitr o phosphorylation, activating dephosphorylation, or both. Med Sci Res 27:17 -19 (C) 1999 Lippincott Williams & Wilkins.