Volume-activated Cl(-)-independent and Cl(-)-dependent K+ pathways in trout red blood cells.
1. Swelling of trout erythrocytes can be induced either by addition of catecholamine to the cell suspension, thus promoting NaCl uptake via beta-adrenergic-stimulated Na(+)-H+ exchange (isotonic swelling) or by suspending red blood cells in a hypotonic medium (hypotonic swelling). In both cases cells tend to regulate their volume by losing K+, but the characteristics of the volume-activated K+ pathways are different: after hormonally induced swelling the K+ loss is strictly Cl- dependent; after hypotonic swelling the K+ loss is essentially Cl- independent. 2. In order to determine the nature of these volume regulatory pathways (i.e. whether the net K+ loss was conductive or was by electroneutral K(+)-H+ exchange or KCl co-transport), studies were performed to analyse ion fluxes and associated electrical phenomena. The cell membrane potential and intracellular ionic activities of volume-regulating and volume-static cells were measured by impalement with conventional microelectrodes and double-barrelled ion-sensitive microelectrodes. 3. The information gained from the electrical and ion flux studies leads to the conclusion that both Cl(-)-independent and Cl(-)-dependent K+ loss proceed via electrically silent pathways. 4. Experiments were designed to distinguish between electroneutral K(+)-H+ exchange or KCl co-transport. These were based upon the inhibition of Cl(-)-OH- exchange to evaluate the degree of coupling between K+ and Cl- (KCl stoichiometry, pH change). The experimental observations are consistent with the fact that both Cl(-)-independent and Cl(-)-dependent K+ loss are mediated by coupled K(+)-anion co-transport and not by K(+)-H+ exchange. 5. On the basis of previous data, we suggest that only one type of K(+)-anion co-transport exists in the cell membrane, for which the selectivity for anions varies according to the change in cellular ionic strength induced by swelling.
Laboratoire Jean Maetz, Département de Biologie Cellulaire et Moléculaire du CEA, Villefranche-sur-Mer, France.
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Guizouarn
B J
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Harvey
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Borgese
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Gabillat
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Garcia-Romeu
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Motais
D000818:Animals; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007545:Isoproterenol / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009994:Osmolar Concentration; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000502:physiology*; D014337:Trout / Q000378:metabolism; D014634:Valinomycin / Q000494:pharmacology
D002712:Chlorides; D014634:Valinomycin; D000254:Sodium-Potassium-Exchanging ATPase; D007545:Isoproterenol