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.
Guizouarn
H
H
Laboratoire Jean Maetz, Département de Biologie Cellulaire et Moléculaire du CEA, Villefranche-sur-Mer, France.
Harvey
B J
BJ
Borgese
F
F
Gabillat
N
N
Garcia-Romeu
F
F
Motais
R
R
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