Pentameric ligand-gated ion channels (pLGICs) constitute a large protein superfamily in metazoa whose role as neurotransmitter receptors mediating rapid, ionotropic synaptic transmission has been extensively studied. Although the vast majority of pLGICs appear to be neurotransmitter receptors, the identification of pLGICs in non-neuronal tissues and homologous pLGIC-like proteins in prokaryotes points to biological functions, possibly ancestral, that are independent of neuronal signalling. Here, we report the molecular and physiological characterization of a highly divergent, orphan pLGIC subunit encoded by the pHCl-2 (CG11340) gene, in Drosophila melanogaster. We show that pHCl-2 forms a channel that is insensitive to a wide array of neurotransmitters, but is instead gated by changes in extracellular pH. pHCl-2 is expressed in the Malpighian tubules, which are non-innervated renal-type secretory tissues. We demonstrate that pHCl-2 is localized to the apical membrane of the epithelial principal cells of the tubules and that loss of pHCl-2 reduces urine production during diuresis. Our data implicate pHCl-2 as an important source of chloride conductance required for proper urine production, highlighting a novel role for pLGICs in epithelial tissues regulating fluid secretion and osmotic homeostasis.
The authors declare no competing or financial interests.
D.F., J.A.D. and L.N. conceptualized experiments and wrote the manuscript. D.F. and T.S. performed experiments. J.A.D. and L.N. provided supervision, and J.A.D. secured funding. M.J.O. provided expertise and feedback on experiments and the manuscript.
This work was supported by Natural Sciences and Engineering Research Council of Canada Discovery Grants (RGPIN 227828-10 and RGPIN 23898-2007), Natural Sciences and Engineering Research Council of Canada Collaborative Research and Development Grant (CRDPJ 401634-10) and Chemtura Canada Co.
- Received April 7, 2016.
- Accepted June 13, 2016.
- © 2016. Published by The Company of Biologists Ltd