Intracellular pH regulation in trout urinary bladder epithelium: Na(+)-H+(NH4+) exchange.
We measured intracellular pH (pHi) of single epithelial cells in situ in the urinary bladder epithelium using microspectrofluorometry and the cytoplasmically trapped pH-sensitive fluorophore, 2',7'-bis(2-carboxyethyl)-5(6)- carboxyfluorescein (BCECF). The resting pHi was 7.21 +/- 0.03 (n = 40 bladders, 489 cells) in pH 7.8 bathing solutions, indicating that H+ is not passively distributed across the plasma membrane and is extruded against its electrochemical gradient. Whereas exposure to hypercapnia (5% CO2 saturation) reversibly decreased pHi, mucosally added 20 mM NH4+ reversibly increased pHi. Recovery from the NH4+ effect was slow and lacked an acid-load pHi undershoot; this is interpreted as suggesting significant NH4+ permeability. Recovery from hypercapnic acidosis was blocked by mucosally added amiloride, indicating that apical Na(+)-H+ exchange is involved in pHi regulation. Addition of 0.5 mM NH4+ to the basolateral side when the mucosal side was bathed in mock urine (2 mM NaCl) significantly increased undirectional mucosal-to-serosal Na+ flux, and the increase was blocked by mucosally added amiloride. We conclude that an apically located Na(+)-H+ exchange is important in pHi regulation and may also accept NH4+ as the counterion for Na+.
Marshall
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WS
Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia, Canada.
Bryson
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SE
D000584:Amiloride / Q000494:pharmacology; D000641:Ammonia / Q000494:pharmacology*; D000818:Animals; D002245:Carbon Dioxide / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008856:Microscopy, Fluorescence / Q000379:methods; D009092:Mucous Membrane / Q000187:drug effects / Q000502:physiology; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers; D014337:Trout; D001743:Urinary Bladder / Q000187:drug effects / Q000502:physiology*
D002352:Carrier Proteins; D002712:Chlorides; D005452:Fluoresceins; D005456:Fluorescent Dyes; D017923:Sodium-Hydrogen Exchangers; C057433:2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester; D002245:Carbon Dioxide; D000641:Ammonia; D000584:Amiloride; D012964:Sodium