High glucose condition activates protein tyrosine phosphatases and deactivates insulin receptor function in...

To investigate the mechanism for the impairment of insulin receptor kinase activity induced by high glucose (HG) in Rat 1 fibroblasts that expressed human insulin receptors (HIRc), we measured protein tyrosine phosphatase (PTPase) activity in HG cells. Incubating HIRc cells for 4 days in 27 mM D-glucose (HG) stimulated cytosolic PTPase activities, but not particulate PTPase activity as determined by two methods using the dephosphorylation of insulin receptors. Furthermore, PTP1B, a major non-transmembrane PTPase in the cytosolic fraction, was increased in HG cells according to Western blots. These results indicate that desensitization of insulin receptor function by a high glucose condition is associated with the activation of PTPase activity.