title: Novel acid-activated fluorophores reveal a dynamic wave of protons in the intestine of Caenorhabditis elegans.
abstract: Unlike the digestive systems of vertebrate animals, the lumen of the alimentary canal of Caenorhabditis elegans is unsegmented and weakly acidic (pH ~4.4), with ultradian fluctuations to pH > 6 every 45-50 s. To probe the dynamics of this acidity, we synthesized novel acid-activated fluorophores termed Kansas Reds. These dicationic derivatives of rhodamine B become concentrated in the lumen of the intestine of living C. elegans and exhibit tunable pKa values (2.3-5.4), controlled by the extent of fluorination of an alkylamine substituent, that allow imaging of a range of acidic fluids in vivo. Fluorescence video microscopy of animals freely feeding on these fluorophores revealed that acidity in the C. elegans intestine is discontinuous; the posterior intestine contains a large acidic segment flanked by a smaller region of higher pH at the posterior-most end. Remarkably, during the defecation motor program, this hot spot of acidity rapidly moves from the posterior intestine to the anterior-most intestine where it becomes localized for up to 7 s every 45-50 s. Studies of pH-insensitive and base-activated fluorophores as well as mutant and transgenic animals revealed that this dynamic wave of acidity requires the proton exchanger PBO-4, does not involve substantial movement of fluid, and likely involves the sequential activation of proton transporters on the apical surface of intestinal cells. Lacking a specific organ that sequesters low pH, C. elegans compartmentalizes acidity by producing of a dynamic hot spot of protons that rhythmically migrates from the posterior to anterior intestine.
authors.affiliation: Department of Medicinal Chemistry, The University of Kansas, Lawrence, KS 66045, USA.
authors.forename: Aaron
authors.initials: A
authors.lastname: Bender
authors.forename: Zachary R
authors.initials: ZR
authors.lastname: Woydziak
authors.forename: Liqiang
authors.initials: L
authors.lastname: Fu
authors.forename: Michael
authors.initials: M
authors.lastname: Branden
authors.forename: Zhenguo
authors.initials: Z
authors.lastname: Zhou
authors.forename: Brian D
authors.initials: BD
authors.lastname: Ackley
authors.forename: Blake R
authors.initials: BR
authors.lastname: Peterson
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000032:analysis / Q000138:chemical synthesis / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D015394:Molecular Structure; D011522:Protons
chemical_list: D005456:Fluorescent Dyes; D011522:Protons