SER-7b, a constitutively active Galphas coupled 5-HT7-like receptor expressed in the Caenorhabditis elegans M4 pharyngeal motorneuron

J Neurochem. 2003 Oct;87(1):22-9. doi: 10.1046/j.1471-4159.2003.01967.x.


Serotonin plays a key role in the regulation of pharyngeal pumping in nematodes. We have isolated a Caenorhabditis elegans cDNA (C09B7.1b, ser-7b) with greatest identity to the 5-HT7 receptor family. Membranes from COS-7 cells expressing SER-7b exhibit saturable [3H]-LSD binding (Kd = 45 nm) that is inhibited by serotonin (5-HT) and tryptamine, but not by other physiological biogenic amines. Expression of SER-7b in COS-7 cells results in dramatic increase in basal cAMP levels over untransfected cells that is dependent on expression level. 5-HT further elevates cAMP levels in a dose-dependent manner (pEC50 = 7.5 +/- 0.5). Mammalian 5-HT7 receptor inverse agonists reduce constitutive activity, with methiothepin the most potent (pIC50 = 7.8 +/- 0.1). Ser-7::GFP transcriptional fusions reveal that SER-7b appears to be expressed solely in the M4 pharyngeal motorneuron after hatching. This is the first report of a Galphas coupled biogenic amine receptor in nematodes and the localization of SER-7b in the M4 pharyngeal motorneuron suggests that SER-7b may play a role in the regulation of pharyngeal pumping.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Binding, Competitive
  • COS Cells
  • Caenorhabditis elegans / metabolism*
  • Caenorhabditis elegans Proteins / biosynthesis
  • GTP-Binding Protein alpha Subunits, Gs / chemistry
  • GTP-Binding Protein alpha Subunits, Gs / genetics
  • GTP-Binding Protein alpha Subunits, Gs / metabolism*
  • Heterotrimeric GTP-Binding Proteins / metabolism*
  • Methiothepin / pharmacokinetics
  • Molecular Sequence Data
  • Motor Neurons / metabolism*
  • Pharynx / metabolism*
  • Phylogeny
  • Receptors, Serotonin / genetics*
  • Sequence Homology, Amino Acid
  • Serotonin / pharmacokinetics
  • Serotonin Antagonists / pharmacokinetics


  • Caenorhabditis elegans Proteins
  • Receptors, Serotonin
  • SER-7b protein, C elegans
  • Serotonin Antagonists
  • serotonin 7 receptor
  • Serotonin
  • Methiothepin
  • GTP-Binding Protein alpha Subunits, Gs
  • Heterotrimeric GTP-Binding Proteins