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Journal of Experimental Biology, Vol 201, Issue 5 693-700, Copyright © 1998 by Company of Biologists

JOURNAL ARTICLES

Chloride transport in red blood cells of lamprey Lampetra fluviatilis: evidence for a novel anion-exchange system

A. Y. Bogdanova, A. O. Sherstobitov and G. P. Gusev

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 micromolar) and DIDS (100 micromolar) 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 Km 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.




© The Company of Biologists Ltd 1998