Journal of Neurophysiology, Vol 76, Issue 1 510-519, Copyright © 1996 by APS

ARTICLES

Homomeric and heteromeric ion channels formed from the kainate-type subunits GluR6 and KA2 have very small, but different, unitary conductances

J. R. Howe
Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520-8066, USA.

1. Patch-clamp methods were used to study recombinant glutamate receptor (GluR) ion channels expressed in human embryonic kidney cells (HEK 293) after transfection of the cells with cDNAs encoding kainate (KA)-type GluR subunits. Cells were transiently or stably transfected with the fully edited (R) version of GluR6 or they were contransfected with GluR6(R) and KA2. 2. Concentration-response data were obtained for KA and glutamate activation of homomeric GluR6(R) channels and fitted with Hill-type equations to give values for the agonist concentration at half-maximal activation (EC50), the Hill coefficient (nH), and the maximum current (Imax). Analysis of results obtained in seven cells with KA gave mean values of 0.47 microM and 1.47 for the EC50 and nH, respectively. The corresponding values for glutamate were 32 microM and 1.21 (n = 5). The Imax values obtained for KA and glutamate in the same cells were similar, suggesting that both KA and glutamate are full agonists at homomeric GluR6(R) channels. 3. Spectral density analysis of current noise evoked by KA and glutamate in GluR6(R)-expressing cells, or in outside-out patches from these cells, was used to obtain estimates of the apparent unitary conductance (gamma noise) of homomeric GluR6(R) channels. Results obtained with 10 microM KA in 15 cells gave a mean gamma noise value of 231 fS. The corresponding value from analysis of noise in outside-out patches was 259 fS (n = 4). Spectral density analysis of glutamate-evoked noise in six cells gave a mean gamma noise value of 264 fS. 4. Noise analysis of whole cell currents recorded in GluR6(R)/ KA2-expressing cell gave a mean gamma noise value of 572 fS (n = 9). Unlike homomeric GluR6(R) channels, GluR6(R)/KA2 heteromers were activated by alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) (0.25-5 mM). The mean EC50 for KA activation of GluR6(R)/KA2 channels was 1.62 microM (n = 6). 5. The results indicate that both homomeric GluR6(R) and heteromieric GluR6(R)/KA2 channels have a unitary conductance in the femtosiemen range. The coassembly of KA2 with GluR6(R) results in channels that have a different affinity for AMPA and KA and a two- to threefold larger unitary conductance.

This article has been cited by other articles:

				J.-C. Platel, T. Heintz, S. Young, V. Gordon, and A. Bordey Tonic activation of GLUK5 kainate receptors decreases neuroblast migration in whole-mounts of the subventricular zone J. Physiol., August 15, 2008; 586(16): 3783 - 3793. [Abstract] [Full Text] [PDF]

				T. J. Wilding, E. Fulling, Y. Zhou, and J. E. Huettner Amino Acid Substitutions in the Pore Helix of GluR6 Control Inhibition by Membrane Fatty Acids J. Gen. Physiol., July 1, 2008; 132(1): 85 - 99. [Abstract] [Full Text] [PDF]

				C. Gebhardt and S. G. Cull-Candy Influence of agonist concentration on AMPA and kainate channels in CA1 pyramidal cells in rat hippocampal slices J. Physiol., June 1, 2006; 573(2): 371 - 394. [Abstract] [Full Text] [PDF]

				A.-M. L. Fay and D. Bowie Concanavalin-A reports agonist-induced conformational changes in the intact GluR6 kainate receptor J. Physiol., April 1, 2006; 572(1): 201 - 213. [Abstract] [Full Text] [PDF]

				T. J. Wilding, Y. Zhou, and J. E. Huettner Q/R Site Editing Controls Kainate Receptor Inhibition by Membrane Fatty Acids J. Neurosci., October 12, 2005; 25(41): 9470 - 9478. [Abstract] [Full Text] [PDF]

				D. Bowie External anions and cations distinguish between AMPA and kainate receptor gating mechanisms J. Physiol., March 15, 2002; 539(3): 725 - 733. [Abstract] [Full Text] [PDF]

				A. Robert, S. N. Irizarry, T. E. Hughes, and J. R. Howe Subunit Interactions and AMPA Receptor Desensitization J. Neurosci., August 1, 2001; 21(15): 5574 - 5586. [Abstract] [Full Text] [PDF]

				J. Lerma, A. V. Paternain, A. Rodriguez-Moreno, and J. C. Lopez-Garcia Molecular Physiology of Kainate Receptors Physiol Rev, July 1, 2001; 81(3): 971 - 998. [Abstract] [Full Text] [PDF]

				T. C. Smith, L.-Y. Wang, and J. R. Howe Heterogeneous Conductance Levels of Native AMPA Receptors J. Neurosci., March 15, 2000; 20(6): 2073 - 2085. [Abstract] [Full Text] [PDF]

				T C. Smith, L.-Y. Wang, and J. R Howe Distinct kainate receptor phenotypes in immature and mature mouse cerebellar granule cells J. Physiol., May 15, 1999; 517(1): 51 - 58. [Abstract] [Full Text] [PDF]

				R. Dingledine, K. Borges, D. Bowie, and S. F. Traynelis The Glutamate Receptor Ion Channels Pharmacol. Rev., March 1, 1999; 51(1): 7 - 62. [Abstract] [Full Text] [PDF]

				I. Bureau, S. Bischoff, S. F. Heinemann, and C. Mulle Kainate Receptor-Mediated Responses in the CA1 Field of Wild-Type and GluR6-Deficient Mice J. Neurosci., January 15, 1999; 19(2): 653 - 663. [Abstract] [Full Text] [PDF]

				D. Bowie, G. D. Lange, and M. L. Mayer Activity-Dependent Modulation of Glutamate Receptors by Polyamines J. Neurosci., October 15, 1998; 18(20): 8175 - 8185. [Abstract] [Full Text] [PDF]

				K. E Pemberton, S. M Belcher, J. A Ripellino, and J. R Howe High-affinity kainate-type ion channels in rat cerebellar granule cells J. Physiol., July 15, 1998; 510(2): 401 - 420. [Abstract] [Full Text] [PDF]

				Y. Sahara, N. Noro, Y. Iida, K. Soma, and Y. Nakamura Glutamate Receptor Subunits GluR5 and KA-2 Are Coexpressed in Rat Trigeminal Ganglion Neurons J. Neurosci., September 1, 1997; 17(17): 6611 - 6620. [Abstract] [Full Text] [PDF]