Effect of sodium orthovanadate on the hepatobiliary clearance of rose bengal in streptozotocin-induced diabetic rats

Modulation of Protein Tyrosine Phosphatase Activity Alters the Subunit Assembly in Native N-Methyl-d-aspartate Receptor Complex

The N-methyl-D-aspartate (NMDA) receptor is crucial for development and neuroplasticity as well as excitotoxicity. The biochemical basis of the disassembly and reassembly of NMDA receptor has never been reported. Using coimmunoprecipitation, Western blotting, and mass spectrometry, we show that inhibition of tyrosine phosphatases triggers disassembly of NR1, NR2A, and NR2B in cortical NMDA receptor complexes. Furthermore, the disassembly of the NMDA receptor subunits is immediate, dose-dependent, and reversible and seems to occur through mechanisms linked to Src kinases. Together, these results define a novel role for tyrosine phosphatases in the complex mechanism of NMDA receptor regulation.

Differential effect of vanadate on receptor-mediated endocytosis of the asialoglycoprotein receptor in hepatocytes from normal and diabetic rats

Insulin-dependent diabetes has been shown to affect several aspects of receptor-mediated endocytosis. Since vanadate, a phosphate analogue, is known to exert insulin-like actions in target tissues, we studied the effects of vanadate on the endocytosis of the asialoglycoprotein receptor (ASGP-R) after its administration either in vivo (oral therapy) and/or in vitro by direct incubation of isolated hepatocytes with vanadate. The surface binding, internalization, and degradation of 3H-asialoorosomucoid (3H-ASOR), a prototype ligand of the ASGP-R, were decreased in diabetic rats by approximately 36.5%, 22.3%, and 12.9%, respectively. These values were normalized in diabetic rats treated by vanadate. Similarly, vanadate treatment normalized the biphasic dissociation of 3H-ASOR/ASGP-R complexes by restoring the rapid dissociation process. In contrast, vanadate treatment did not affect any of these endocytic parameters in normal rats. In vitro experiments were monitored by direct incubation of isolated hepatocytes with 10 mM vanadate. This incubation created an inhibitory effect on the endocytic parameters. In this work, we have demonstrated that vanadate treatment can reverse the alterations induced by diabetes on receptor-mediated endocytosis of the ASGP-R.