REDUCTION OF TYROSINE KINASE-ACTIVITY AND PROTEIN-TYROSINE DEPHOSPHORYLATION BY ANOXIC STIMULATION IN-VITRO

Tyrosine-specific protein phosphorylation has been recently implicated in mediating pathological changes associated with cerebral ischemia. In the present study, acute hypoxia/ischemia (anoxia) was simulated in vitro by incubating rat hippocampal slices in glucose free artificial cerebrospinal fluid saturated with 95% N-2/5% CO2. A marked decrease in the level of tyrosine phosphorylation of many protein bands compare d with the control was observed. Immunoprecipitation and western blot confirmed that the NR2A/2B subunits of the N-methyl-D-aspartate recept ors are among the dephosphorylated proteins. Maximal dephosphorylation of bands corresponding to NR2A/2B was reached after 10 min, and no re covery was observed even after 1 h in normal, oxygenated artificial ce rebrospinal fluid. The effect was partially blocked by dephostatin, a membrane-permeable inhibitor of protein tyrosine phosphatases, but was not affected by the presence of glutamate receptor antagonists, or by removing extracellular Ca2+ or chelating intracellular Ca2+. Enzyme a ssay showed that anoxic stimulation resulted in a selective reduction in protein tyrosine kinase activity without affecting protein tyrosine phosphatase activity. Thus the present work suggests that anoxic stim ulation produces a selective inhibition of protein tyrosine kinase act ivity leading to tyrosine-dephosphorylation of several proteins includ ing the N-methyl-D-aspartate receptors. The underlying mechanism may i nvolve a novel signal transduction pathway, which may protect neurons from degeneration during ischemic stress. (C) 1997 IBRO. Published by Elsevier Science Ltd.