title: Potentiation of NMDA receptor-mediated responses by dynorphin at low extracellular glycine concentrations.
abstract: The effect of dynorphin A(1-13) on N-methyl-D-aspartate (NMDA)-activated currents was investigated in the presence of low extracellular glycine concentrations in Xenopus oocytes expressing recombinant heteromeric NMDA receptors and in cultured hippocampal neurons with the use of voltage-clamp techniques. At an extracellular added glycine concentration of 100 nM, dynorphin A(1-13) (10 microM) greatly increased the amplitude of NMDA-activated currents for all heteromeric subunit combinations tested; on average, the potentiation was: epsilon1/zeta1, 3,377 +/- 1,416% (mean +/- SE); epsilon2/zeta1, 1,897 +/- 893%; epsilon3/zeta1, 4,356 +/- 846%; and epsilon4/zeta1, 1,783 +/- 503%. Potentiation of NMDA-activated current by dynorphin A(1-13) was concentration dependent between 0.1 and 10 microM dynorphin A(1-13), with a half-maximal concentration value of 2.77 microM and an apparent Hill coefficient of 2.53, for epsilon2/zeta1 subunits at 100 nM added extracellular glycine. Percentage potentiation by dynorphin A(1-13) was maximal at the lowest glycine concentrations tested (0.01 and 0.1 microM), and decreased with increasing glycine concentration. No significant potentiation was observed at glycine concentrations > 0.1 microM for epsilon1/zeta1, epsilon2/zeta1, and epsilon4/zeta1 subunits, or at > 1 microM for epsilon3/zeta1 subunits. Potentiation of NMDA-activated currents by dynorphin A(1-13) was not inhibited by 1 microM of the kappa-opioid receptor antagonist nor-binaltorphimine, and potentiation was not observed with 10 microM of the kappa-opioid receptor agonist trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl] benzene-acetamide. Potentiation of NMDA-activated current by dynorphin A(1-13) was inhibited by the glycine antagonist kynurenic acid (50 microM). NMDA-activated current was also potentiated at low glycine concentrations by 10 microM dynorphin A(2-13) or (3-13), both of which have a glycine as the first amino acid, but not by 10 microM dynorphin A(4-13), which does not have glycine as an amino acid. In hippocampal neurons, 10 microM dynorphin A(1-13) or (2-13) potentiated steady-state NMDA-activated current in the absence of added extracellular glycine. The extracellular free glycine concentration, determined by high-performance liquid chromatography, was between 26 and 36 nM for the bathing solution in presence or absence of 10 microM dynorphin A(1-13), (2-13), (3-13), or (4-13), and did not differ significantly among these solutions. The observations are consistent with the potentiation of NMDA-activated current at low extracellular glycine concentrations resulting from an interaction of the glycine amino acids in dynorphin A(1-13) with the glycine coagonist site on the NMDA receptor. Because dynorphin A is an endogenous peptide that can be coreleased with glutamate at glutamatergic synapses, the potentiation of NMDA receptor-mediated responses could be an important physiological regulator of NMDA receptor function at these synapses.
authors.affiliation: Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: L
authors.initials: L
authors.lastname: Zhang
authors.forename: R W
authors.initials: RW
authors.lastname: Peoples
authors.forename: M
authors.initials: M
authors.lastname: Oz
authors.forename: J
authors.initials: J
authors.lastname: Harvey-White
authors.forename: F F
authors.initials: FF
authors.lastname: Weight
authors.forename: U
authors.initials: U
authors.lastname: Brauneis
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D004357:Drug Synergism; D004399:Dynorphins / Q000494:pharmacology*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D005998:Glycine / Q000494:pharmacology*; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects; D051379:Mice; D009474:Neurons / Q000187:drug effects; D009865:Oocytes / Q000187:drug effects; D010446:Peptide Fragments / Q000494:pharmacology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists / Q000502:physiology*; D017473:Receptors, Opioid, kappa / Q000187:drug effects; D014982:Xenopus laevis
chemical_list: D000701:Analgesics, Opioid; D018690:Excitatory Amino Acid Agonists; D010446:Peptide Fragments; D016194:Receptors, N-Methyl-D-Aspartate; D017473:Receptors, Opioid, kappa; C026843:dynorphin (1-13); D004399:Dynorphins; D005998:Glycine