Article

Heteromultimers of DEG/ENaC subunits form H+-gated channels in mouse sensory neurons.

Department of Internal Medicine and Psychiatry, and Howard Hughes Medical Institute, University of Iowa College of Medicine, Iowa City, IA 52242, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 03/2002; 99(4):2338-43. DOI: 10.1073/pnas.032678399
Source: PubMed

ABSTRACT Acidic extracellular solution activates transient H(+)-gated currents in dorsal root ganglion (DRG) neurons. The biophysical properties of three degenerin/epithelial sodium (DEG/ENaC) channel subunits (BNC1, ASIC, and DRASIC), and their expression in DRG, suggest that they might underlie these H(+)-gated currents and function as sensory transducers. However, it is uncertain which of these DEG/ENaC subunits generate the currents, and whether they function as homomultimers or heteromultimers. We found that the biophysical properties of transient H(+)-gated currents from medium to large mouse DRG neurons differed from BNC1, ASIC, or DRASIC expressed individually, but were reproduced by coexpression of the subunits together. To test the contribution of each subunit, we studied DRG from three strains of mice, each bearing a targeted disruption of BNC1, ASIC, or DRASIC. Deletion of any one subunit did not abolish H(+)-gated currents, but altered currents in a manner consistent with heteromultimerization of the two remaining subunits. These data indicate that combinations of two or more DEG/ENaC subunits coassemble as heteromultimers to generate transient H(+)-gated currents in mouse DRG neurons.

0 Followers
 · 
103 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Acid sensing ion channels (ASICs) generate H(+) -gated Na(+) currents that contribute to neuronal function and animal behavior. Like ASIC1, ASIC2 subunits are expressed in the brain and multimerize with ASIC1 to influence acid-evoked currents and facilitate ASIC1 localization to dendritic spines. To better understand how ASIC2 contributes to brain function, we localized the protein and tested the behavioral consequences of ASIC2 gene disruption. For comparison, we also localized ASIC1 and studied ASIC1(-/-) mice. ASIC2 was prominently expressed in areas of high synaptic density, and with a few exceptions, ASIC1 and ASIC2 localization exhibited substantial overlap. Loss of ASIC1 or ASIC2 decreased freezing behavior in contextual and auditory cue fear conditioning assays, in response to predator odor, and in response to CO2 inhalation. In addition, loss of ASIC1 or ASIC2 increased activity in a forced swim assay. These data suggest that ASIC2, like ASIC1, plays a key role in determining the defensive response to aversive stimuli. They also raise the question of whether gene variations in both ASIC1 and ASIC2 might affect fear and panic in humans.
    Genes Brain and Behavior 11/2013; 13(2). DOI:10.1111/gbb.12108 · 3.51 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Acid sensing ion channels (ASICs) and their interaction partners of the stomatin family have all been implicated in sensory transduction. Single gene deletion of asic3, asic2, stomatin, or stoml3 all result in deficits in the mechanosensitivity of distinct cutaneous afferents in the mouse. Here, we generated asic3-/-:stomatin-/-, asic3-/-:stoml3-/- and asic2-/-:stomatin-/- double mutant mice to characterize the functional consequences of stomatin-ASIC protein interactions on sensory afferent mechanosensitivity. The absence of ASIC3 led to a clear increase in mechanosensitivity in rapidly adapting mechanoreceptors (RAMs) and a decrease in the mechanosensitivity in both Aδ- and C-fibre nociceptors. The increased mechanosensitivity of RAMs could be accounted for by a loss of adaptation which could be mimicked by local application of APETx2 a toxin that specifically blocks ASIC3. There is a substantial loss of mechanosensitivity in stoml3-/- mice in which ~35% of the myelinated fibres lack a mechanosensitive receptive field and this phenotype was found to be identical in asic3-/-:stoml3-/- mutant mice. However, Aδ-nociceptors showed much reduced mechanosensitivity in asic3-/-:stoml3-/- mutant mice compared to asic3-/- controls. Interestingly, in asic2-/-:stomatin-/- mutant mice many Aδ-nociceptors completely lost their mechanosensitivity which was not observed in asic2-/- or stomatin-/- mice. Examination of stomatin-/-:stoml3-/- mutant mice indicated that a stomatin/STOML3 interaction is unlikely to account for the greater Aδ-nociceptor deficits in double mutant mice. A key finding from these studies is that the loss of stomatin or STOML3 in asic3-/- or asic2-/- mutant mice markedly exacerbates deficits in the mechanosensitivity of nociceptors without affecting mechanoreceptor function.
    The Journal of Physiology 08/2013; 591(22). DOI:10.1113/jphysiol.2013.261180 · 4.54 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Protonation of several amino acid residues in the extracellular domain (ECD) of acid-sensing ion channel (ASIC) causes conformational changes that lead to opening of the channel. It is not clear how conformational changes in ECD are coupled to channel gating. Here, we show that the loop connecting β9 and α4 at the base of the thumb region of ECD interacts with post-TM1 to stabilize the channel in the closed state. Flexibility of these two regions is important for optimum gating of the channel. In ASIC1a, when Y71 (post-TM1) and W287 (β9-α4 loop) were mutated to cysteine, they formed disulfide bond in the closed state. Breaking of the disulfide bond by reducing agent dithiothreitol (DTT) or tris(2-carboxyethyl)phosphine (TCEP) potentiated the current significantly. Engineered cysteine G288C reacted with sulfhydryl-specific methanethiosulfonate ethyltrimethylammonium (MTSET) in the open state but not in closed/steady desensitized state, suggesting gating-associated conformational movement of this loop. We also identified a salt bridge between highly conserved R64 at TM1 and D432 at TM2 that is important for optimum gating.Based on our results and other published work, we propose that proton binding in ECD is followed by the displacement of the β9-α4 loop of the thumb, leading to the rotation of TM1. Conformational movement propagates to TM2 and the channel gate opens by the concomitant movement of TM2 and breaking of the salt bridge between R64 and D432.
    Journal of Molecular Neuroscience 03/2013; DOI:10.1007/s12031-013-9991-x · 2.76 Impact Factor

Preview

Download
0 Downloads
Available from