Chloride transport in red blood cells of lamprey Lampetra fluviatilis: evidence for a novel anion-exchange system.
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.
Bogdanova AYu
Laboratory of Comparative Biochemistry of Inorganic Ions, Sechenov Institute, Russian Academy of Sciences, St Petersburg, Russia.
Sherstobitov
A O
AO
Gusev
G P
GP
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
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