Changes in tyrosine phosphorylation in neocortex following transient cerebral ischaemia.

Growth factor receptors activate protein tyrosine kinases, which are important for cell growth and survival. The protein tyrosine kinase (PTK) activity and the levels of phosphotyrosine (Ptyr) containing proteins were studied in the rat neocortex exposed to 15 min of transient cerebral ischaemia. The levels of the Ptyr containing proteins increase during recovery in the synaptosomal fraction, while the changes in the light membrane fraction are less marked. Protein tyrosine phosphorylation in the cytosol decreases. The differential changes in the levels of phosphotyrosine proteins in the particulate and cytosolic fractions suggest that the signal cascade from membrane bound receptors through tyrosine phosphorylation in the cytosol may be interrupted following ischaemia. This may be of importance for the development of neuronal damage.