title: Chloride transport in red blood cells of lamprey Lampetra fluviatilis: evidence for a novel anion-exchange system.
abstract: The existence of a furosemide-sensitive Cl- transport pathway activated by external Ca2+ and Mg2+ has been demonstrated previously in studies of Cl- influx across the lamprey erythrocyte membrane. The aim of the present study was to characterize further specific Cl- transport pathways, especially those involved in Cl- efflux, in the red blood cell membrane of Lampetra fluviatilis. Cl- efflux was inhibited by 0.05 mmol l-1 dihydroindenyloxyalkanoic acid (DIOA) (81%), 1 mmol l-1 furosemide (76%) and 0.1 mmol l-1 niflumic acid (54%). Bumetanide (100 mumol l-1) and DIDS (100 mumol l-1) had no effect effect on Cl- efflux. Substitution of external Cl- by gluconate, but not by NO3-, led to a gradual decline of Cl- efflux. In addition, the removal of external Ca2+ resulted in a significant reduction in the rate of Cl- efflux. Membrane depolarization caused by increasing external K+ concentration or by inhibiting K+ channels with 1 mmol l-1 Ba2+ did not affect Cl- efflux. The furosemide-sensitive component of Cl- influx was a saturable function of external [Cl-] with an apparent K(m) of approximately 92 mmol l-1 and Vmax of approximately 17.8 mmol l-1 cells-1 h-1. Furosemide did not affect intracellular Cl- concentration (57.6 +/- 5.2 mmol l-1 cell water), measured using an ion-selective Cl- electrode, showing that a furosemide-sensitive pathway is not involved in net Cl- movement. A gradual fall (from 28.1 +/- 1.4 to 15.0 +/- 1.3 mmol l-1 cells-1 h-1) in unidirectional Cl- influx with time was observed within 3 h of cell preincubation in the standard physiological medium. These data provide evidence for the existence for an electroneutral furosemide-sensitive anion-exchange pathway in the lamprey erythrocyte membrane that accepts chloride and nitrate, but not bicarbonate or bromide.
authors.affiliation: Laboratory of Comparative Biochemistry of Inorganic Ions, Sechenov Institute, Russian Academy of Sciences, St Petersburg, Russia.
authors.lastname: Bogdanova AYu
authors.forename: A O
authors.initials: AO
authors.lastname: Sherstobitov
authors.forename: G P
authors.initials: GP
authors.lastname: Gusev
mesh_terms: D000818:Animals; D000838:Anions; D001464:Barium / Q000494:pharmacology; D001639:Bicarbonates / Q000494:pharmacology; D001965:Bromides / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent; D002712:Chlorides / Q000097:blood*; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D005665:Furosemide / Q000494:pharmacology; D005942:Gluconates / Q000494:pharmacology; D017136:Ion Transport; D007700:Kinetics; D007798:Lampreys / Q000097:blood*; D009566:Nitrates / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology
chemical_list: D000838:Anions; D001639:Bicarbonates; D001965:Bromides; D002413:Cations, Divalent; D002712:Chlorides; D005942:Gluconates; D009566:Nitrates; D001464:Barium; D005665:Furosemide; C030691:gluconic acid; D011188:Potassium; D002118:Calcium