Insulin modulation of cloned mouse NMDA receptor currents in Xenopus oocytes

Modulation of recombinant N-methyl-D-aspartate receptor (NMDAR) currents by insulin was studied using the Xenopus oocyte expression system. Insulin (0.8 mu M, to min) regulated NMDAR currents in a subunit-specific manner. Currents from epsilon 1/zeta 1, epsilon 2/zeta 1, and epsilon 4/zeta 1 receptors were variably potentiated, whereas currents from epsilon 3/zeta 1 receptors were not. Protein tyrosine kinases (PTKs) and protein kinase C were found to be involved in insulin-mediated modulation in an NMDAR subtype-specific way. Pretreatment with a specific PTK inhibitor, lavendustin A, attenuated and blocked the insulin effect on epsilon 2/zeta 1 and epsilon 4/zeta 1, respectively. Preincubation with selective protein kinase C inhibitors, staurosporine or calphostin C, depressed the response of epsilon 1/zeta 1 and epsilon 2/zeta 1 receptors to insulin. Basal regulation of NMDAR currents by endogenous PTKs and protein tyrosine phosphatases (PTPs) was also investigated. Of the four receptor subtypes, only epsilon 1/zeta 1 receptor currents were affected by basal PTK inhibition via lavendustin A, whereas PTP inhibition by phenylarsine oxide or orthovanadate enhanced currents from epsilon 1/zeta 1 and epsilon 2/zeta 1 receptors. Surprisingly, a stimulatory PTP modulation was observed for epsilon 4/zeta 1. As NMDAR subunits are differentially expressed in the brain, the observed subtype-specific modulations of NMDAR currents by insulin, PTKs, and PTPs may provide important insights into certain NMDAR-dependent physiological and pathological processes.