Evidence for a K(+)‐H+ exchange in trout red blood cells.

Abstract

SUMMARY1. Exposure of trout red blood cells to ,-adrenergic agonist isoprenaline activates a cAMP-dependent Na+-H+ antiport, the movements of protons being compensated by a Cl--OH-(or HCO3) exchange mediated by band 3 protein. The absorption of water osmotically linked to sodium and chloride induces cell swelling.2. In the presence of acetazolamide, anionic exchange is inhibited and activation of cationic exchange resulted in the first 2 min in a strong external acidification and a large internal alkalinization leading to a reversal of the transmembrane pH gradient. Then, for at least 1 h and despite the inhibition of Cl-entry, a net Na+ uptake occurred which was balanced by an equivalent K+ loss, with the result that cell volume and pH gradient remained unchanged.3. In such conditions, the inactivation of the Na+-H+ exchanger by a /8-antagonist, propanolol, blocked Na+ entry while K+ continued to be lost. This volume-independent K+ efflux, which is thus independent of the Na+-H+ exchanger, was not accompanied by a Cl-efflux but was associated with large internal and external pH changes consistent with K+-H+ exchange.4. The K+ loss and the related pH changes are inhibited by compounds which are known to inhibit the K+-anion co-transporter in trout red cells, i.e. 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (Dids) and niflumic acid.

K+‐H+ Exchange Activity in Brush‐Border Membrane Vesicles Isolated from Chick Small Intestine

“…A K+-H' exchanger has also been reported to be expressed in the membrane of rabbit corneal epithelium (Bonanno, 1991), carotid body glomus cells (Wilding et al, 1992), red blood cells (Fievet et al, 1993) and Amphiuma erythrocytes (Cala, 1980). In summary, our results demonstrate that BBMV isolated from chicken jejunum express at least two separate cation H+ exchangers, one mainly for K' and one for Na+.…”

Volume‐activated Cl(‐)‐independent and Cl(‐)‐dependent K+ pathways in trout red blood cells.

“…the taurine pathway as well as Cl--dependent or Cl--independent pathways (Borgese et al 1987a; Garcia-Romeu et al 1991; Motais et al 1991). This difficulty can be circumvented by using acetazolamide (Diamox), which effectively C1--DEPENDENT AND C1--INDEPENDENT CO-TRANSPORT 621 inhibits Cl--OH-exchange as demonstrated in the companion paper (Fievet et al 1993); we showed that in the presence of acetazolamide, Cl-entry via the anion exchanger is completely blocked whereas the activation of Na+-H+ exchange induced large changes in external and internal pH even leading to a reversal of the transmembrane pH gradient. Despite the persistence of this large transmembrane pH gradient, inhibition of the anion exchanger by acetazolamide was clearly maintained during the 1 h experiment.…”

“…Preparation of cells, determination of cellular ion and water contents and intracellular pH measurements were made as described in the companion paper (Fievet, Guizouarn, Pellissier, Garcia-Romeu & Motais, 1993 …”

“…Experiments designed to distinguish between these two modes of transport were based upon the inhibition of Cl--OH-exchange with acetazolamide in order to uncover the nature of the KCl-coupled transport (Fievet et al 1993). The data showed that net K+ loss is not affected by inhibition of Cl--OH+ exchange for at least 1 h (Fig.…”

Physiological responses to handling in the turbot

“…This does suggest that the source of the increased plasma K + concentrations may have differed from that of the other monovalent ions. We suspect that this may have reflected an increased K + efflux from erythrocytes (Fievet et al, 1993) and/or other cell types (Bianchini et al, 1991) as a volume-regulatory process during stress. Indeed, turbot red cells showed no cell swelling after stress as determined by their stable MCHC.…”