The composition of the GABA receptor at the Caenorhabditis elegans neuromuscular junction

Br J Pharmacol. 2005 Feb;144(4):502-9. doi: 10.1038/sj.bjp.0706052.


1. The unc-49 gene of the nematode Caenorhabditis elegans encodes three gamma-aminobutyric acid type A (GABA(A)) receptor subunits. Two of these, UNC-49B and UNC-49C, are expressed at high abundance and co-localize at the neuromuscular junction. 2. The UNC-49B subunit is sufficient to form a GABA(A) receptor in vitro and in vivo. Furthermore, all loss-of-function unc-49 alleles lack functional UNC-49B. No mutations specifically inactivate UNC-49C. Thus, UNC-49C appears to be dispensable for receptor function; however, UNC-49C has been conserved among different nematode species, suggesting it plays a necessary role. 3. To ascertain whether UNC-49C is part of the GABA(A) receptor in vivo, we performed patch-clamp electrophysiology on C. elegans muscle cells. Sensitivity to GABA, and to the antagonists picrotoxin and pregnenolone sulfate, matched the UNC-49B/C heteromer rather than the UNC-49B homomer, for both exogenous and synaptically-released GABA. 4. The synaptic localization of UNC-49C requires the presence of UNC-49B, indicative of a physical association between the two subunits in vivo. Thus, the in vivo receptor is an UNC-49B/C heteromer. 5. UNC-49C plays a negative modulatory role. Using the rapid ligand-exchange technique in vitro, we determined that UNC-49C causes accelerated receptor desensitization. Previously, UNC-49C was shown to reduce single-channel conductance in UNC-49B/C heteromers. Thus, the function of UNC-49B is to provide GABA responsiveness and localization to synapses, while the function of UNC-49C is to negatively modulate receptor function and precisely shape inhibitory postsynaptic currents.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alternative Splicing
  • Animals
  • Caenorhabditis elegans / genetics
  • Caenorhabditis elegans / metabolism*
  • Caenorhabditis elegans Proteins / genetics*
  • Cloning, Molecular
  • DNA, Complementary / metabolism
  • Exons
  • Genes, Helminth*
  • Neuromuscular Junction / genetics
  • Neuromuscular Junction / metabolism*
  • Patch-Clamp Techniques
  • Protein Subunits
  • Receptors, GABA-A / genetics*
  • Synaptic Transmission* / genetics
  • Transfection


  • Caenorhabditis elegans Proteins
  • DNA, Complementary
  • Protein Subunits
  • Receptors, GABA-A