title: Fluorescence measurements of serotonin-induced V-ATPase-dependent pH changes at the luminal surface in salivary glands of the blowfly Calliphora vicina.
abstract: Secretion in blowfly salivary glands is induced by the neurohormone serotonin and powered by a vacuolar-type H(+)-ATPase (V-ATPase) located in the apical membrane of the secretory cells. We have established a microfluorometric method for analysing pH changes at the luminal surface of the secretory epithelial cells by using the fluorescent dye 5-N-hexadecanoyl-aminofluorescein (HAF). After injection of HAF into the lumen of the tubular salivary gland, the fatty acyl chain of the dye molecule partitions into the outer leaflet of the plasma membrane and its pH-sensitive fluorescent moiety is exposed at the cell surface. Confocal imaging has confirmed that HAF distributes over the entire apical membrane of the secretory cells and remains restricted to this membrane domain. Ratiometric analysis of HAF fluorescence demonstrates that serotonin leads to a reversible dose-dependent acidification at the luminal surface. Inhibition by concanamycin A confirms that the serotonin-induced acidification at the luminal surface is due to H(+) transport across the apical membrane via V-ATPase. Measurements with pH-sensitive microelectrodes corroborate a serotonin-induced luminal acidification and demonstrate that luminal pH decreases by about 0.4 pH units at saturating serotonin concentrations. We conclude that ratiometric measurements of HAF fluorescence provide an elegant method for monitoring V-ATPase-dependent H(+) transport in the blowfly salivary gland in vivo and for analysing the spatiotemporal pattern of pH changes at the luminal surface.
authors.affiliation: Institut für Biochemie und Biologie, Universität Potsdam, D-14415 Potsdam, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Rein
authors.forename: Bernhard
authors.initials: B
authors.lastname: Zimmermann
authors.forename: Carsten
authors.initials: C
authors.lastname: Hille
authors.forename: Ingo
authors.initials: I
authors.lastname: Lang
authors.forename: Bernd
authors.initials: B
authors.lastname: Walz
authors.forename: Otto
authors.initials: O
authors.lastname: Baumann
mesh_terms: D000818:Animals; D004175:Diptera / Q000201:enzymology*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D019476:Insect Proteins; D018942:Macrolides / Q000494:pharmacology; D008839:Microelectrodes; D012469:Salivary Glands / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000378:metabolism* / Q000494:pharmacology; D018490:Serotonin Agents / Q000494:pharmacology; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D019476:Insect Proteins; D018942:Macrolides; D018490:Serotonin Agents; D012701:Serotonin; C036978:concanamycin A; D025262:Vacuolar Proton-Translocating ATPases