title: Two-photon fluorescence lifetime imaging of intracellular chloride in cockroach salivary glands.
abstract: Although chloride plays an important role in many cellular processes, there is a lack of data about intracellular chloride concentrations [Cl(-)](i), particularly due to technical problems. To overcome that, in this study fluorescence lifetime imaging microscopy in the time-domain by using time-correlated single-photon counting was combined with two-photon excitation (2P-FLIM). This 2P-FLIM setup has been successfully used with the Cl(-)-sensitive fluorescent dye N-(ethoxycarbonylmethyl)-6-methoxy-quinolinium bromide (MQAE) in order to measure [Cl(-)](i) in cockroach salivary glands, a well-established model system for studying epithelial ion transport processes. MQAE was well suitable for two-photon excitation, when loaded into cells, and displayed a sufficient dynamic range of its fluorescence decay time changes in response to variation of [Cl(-)](i) according to the Stern-Volmer relationship. On this basis a uniform [Cl(-)](i) in the range of 42-80 mM with a mean value of 59 mM +/- 1 mM was found in resting cockroach salivary ducts, indicating active Cl(-) accumulation. However, exposure to Cl(-)-free saline caused only a moderate [Cl(-)](i) drop to 48 mM +/- 4 mM, suggesting a relatively low basolateral Cl(-) permeability in ducts, at least under resting conditions. Additionally, bath application of the biogenic amine dopamine, known to stimulate the saliva modification in the ducts, caused no significant [Cl(-)](i) changes. These results suggest a more complex scenario of [Cl(-)](i) homeostasis in cockroach salivary ducts. In conclusion, 2P-FLIM seems to be a suitable technique for quantitative [Cl(-)](i) measurements in many biological systems.
authors.affiliation: Physical Chemistry/Applied Laser Sensing, Institute of Chemistry & Interdisciplinary Center for Photonics, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany. hille@uni-potsdam.de
authors.forename: Carsten
authors.initials: C
authors.lastname: Hille
authors.forename: Mattes
authors.initials: M
authors.lastname: Lahn
authors.forename: Hans-Gerd
authors.initials: HG
authors.lastname: Löhmannsröben
authors.forename: Carsten
authors.initials: C
authors.lastname: Dosche
mesh_terms: D000818:Animals; D002712:Chlorides / Q000032:analysis*; D003058:Cockroaches / Q000737:chemistry / Q000528:radiation effects; D005456:Fluorescent Dyes / Q000737:chemistry; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D017785:Photons; D011806:Quinolinium Compounds / Q000737:chemistry; D012469:Salivary Glands / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D002712:Chlorides; D005456:Fluorescent Dyes; D011806:Quinolinium Compounds; C085493:N-(ethoxycarbonylmethyl)-6-methoxyquinolinium