Catecholamine-induced transport systems in trout erythrocyte. Na+/H+ countertransport or NaCl cotransport?

Abstract

It has previously been shown (Baroin, A,, F . Garcia-Romeu, T . Lamarre, and R . Motais . 1984a, b . Journal of Physiology . 350 :137, 356 :21 ; Mahe, Y ., F . Garcia-Romeu, and R . Motais . 1985 . European Journal of Pharmacology . 116 :199) that the addition of catecholamines to an isotonic suspension of nucleated red blood cells of the rainbow trout first stimulates a cAMPdependent, amiloride-sensitive Na'/H' exchange . This stimulation seems to be transient . It is followed by a more permanent activation of a coupled entry of Na' and Cl -, which is inhibited by amiloride but also by inhibitors of band 3 protein (DIDS, furosemide, niflumic acid) . The coupled entry of Na' and Clcould therefore result from the parallel and simultaneous exchange of Na .' for H (via the cAMP-dependent Na'/H' antiporter) and Clo-, for HCO3-; (via the anion exchange system located in band 3 protein) . However, in view of the following arguments, it had been proposed that NaCI uptake does not proceed by the double-exchanger system but via an NaCI cotransport : (a) Na' entry requires Cl -as anion (in NO-3 medium, the Na uptake is strongly inhibited, whereas NO-3 is an extremely effective substitute for Cl-in the anion exchange system) ; (b) Na uptake is not significantly affected by the presence of HCO-3 in the suspension medium despite the fact that in red cells, CI-/HCO-exchange occurs more readily than the exchanges of Cl -for basic equivalents in a theoretically C0 2-free medium (the so-called Cl -/OH-exchanges) . The purpose of the present paper was a reassessment of the two models by using monensin, an ionophore allowing Na'/H' exchange . From this study, it appears that NaCl entry results from the simultaneous functioning of the Na'/H' antiporter and the anion exchange system . The apparent Cl dependence is explained by the fact that, in these erythrocytes, NO-clearly inhibits the turnover rate of the Na'/H' antiporter . As Na'/H' exchange is the driving component in the salt uptake process, this inhibition explains the Cl requirement for Na entry . The lack of stimulation of cell swelling by bicarbonate is explained by the fact that the rate of anion exchange in a C0 2-free medium (Cl-/OH -exchange) is roughly equivalent to that of Na'/H' exchange and thus in practice is not limiting to the net influx of NaCl through the two exchangers . The acidification J . GEN . PHYSIOL .

Do HbSS erythrocytes lose KCl in physiological conditions?

“…Cell water content was measured as described as Borgese et al (1986). Briefly, after the incubation period, cells were resuspended at about 30% haematocrit, and poured into nylon tubes which were then centrifuged at 15 000 g for 10 min in a Sorvall refrigerated centrifuge.…”

Different effects of alpha- and beta-adrenergic stimulation on cytosolic pH and myofilament responsiveness to Ca2+ in cardiac myocytes.

“…In Necturus gallbladder epithelium18 and in renal brush border vesicles,'9 an increase in cAMP reduces the rate of Na+-H+ exchange and leads to a decrease in pHi, whereas the opposite occurs in trout red blood cells. 20,21 The purpose of this study was to establish 1) the effect of a-and ,3-adrenergic stimulation on pHi of single myocardial cells, 2) whether the changes in pHi that occurred in response to these interventions were Isolation Procedure Ventricular myocytes were enzymatically dissociated with minor modifications of a technique previously described. 22 Briefly, 2-4-month-old male Wistar rats from the Gerontology Research Center Colony were subjected to narcosis with an intraperitoneal injection of sodium pentobarbital.…”

Control of cell volume and ion transport by beta‐adrenergic catecholamines in erythrocytes of rainbow trout, Salmo gairdneri.

“…The strong acidification of the medium which occurs at the onset of stimulation has been explained by the fact that part of the Na+ that penetrates the cell is exchanged with H+, which comes from the intracellular buffer, via a Na+-H+ exchange mechanism with a stocheiometry of 1: 1 (Baroin et al 1984b; Cossins & Richardson, 1985). In spite of the fact that NaCl uptake is practically independent of the presence of HCO3-in the external medium and swelling is largely inhibited when Cl-is replaced by N03-, it was suggested that the catecholamine-induced volume increase is mediated by the activation of a Na+-H+ antiport which operates in parallel to a Cl--OH-exchanger, rather than by a NaCl co-transport (Borgese, Garcia-Romeu & Motais, 1986). It should be noted that other systems such as Amphiuma and dog erythrocytes and human blood lymphocytes regulate their volume in response to osmotic shrinkage by the stimulation of a Na+-H+ antiport operating in parallel to a Cl--HC13-exchanger (Cala, 1980(Cala, , 1983bParker, 1983b;Parker & Castranova, 1984;Grinstein, Clarke & Rothstein, 1983;Kregenow, Caryk & Siebens, 1985).…”