Insulin promotes rapid delivery of N-methyl-D-aspartate receptors to the cell surface by exocytosis

Insulin potentiates N-methyl-D-aspartate receptors (NMDARs) in neurons and Xenopus oocytes expressing recombinant NMDARs. The present study shows that insulin induced (i) an increase in channel number times open probability ( nP(o)) in outside-out patches excised from Xenopus oocytes, with no change in mean open time, unitary conductance, or reversal potential, indicating a n increase in n and/or P-o; (ii) an increase in charge transfer during bloc k of NMDA-elicited currents by the open channel blocker MK-801, indicating increased number of functional NMDARs in the cell membrane with no change i n P-o; and (iii) increased NR1 surface expression, as indicated by Western blot analysis of surface proteins. Botulinum neurotoxin A greatly reduced i nsulin potentiation, indicating that insertion of new receptors occurs via SNARE-dependent. exocytosis. Thus, insulin potentiation occurs via delivery of new channels to the plasma membrane. NMDARs assembled from mutant subun its lacking all known sites of tyrosine and serine/threonine phosphorylatio n in their carboxyl-terminal tails exhibited robust insulin potentiation, s uggesting that insulin potentiation does not require direct phosphorylation of NMDAR subunits. Because insulin and insulin receptors are localized to glutamatergic synapses in the hippocampus, insulin-regulated trafficking of NMDARs may play a role in synaptic transmission and plasticity, including long-term potentiation.