Control of red cell volume and pH in trout: Effects of isoproterenol, transport inhibitors, and extracellular pH in bicarbonate/carbon dioxide-buffered media (original) (raw)
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Journal of Experimental Biology, 1999
The transport pathways mediating regulatory volume increase (RVI) and β-adrenergic responses in red cells of the European flounder Platichthys flesus have been investigated. Hypertonic treatment under a low-PO2 atmosphere led to a complete RVI and to a three- to fourfold increase in Na+ influx. The RVI and the activated Na+ influx were blocked by the transport inhibitors amiloride and 4, 4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS), both at a concentration of 10(−4)mol l-1, and the RVI was abolished in a Na+-free saline, indicating the involvement of a hypertonically induced Na+/H+ exchanger and an accompanying Cl-/HCO3- exchanger. Both the hypertonically induced Na+ influx and the RVI were blocked by oxygenation of shrunk cells. The β-adrenergic agonist isoproterenol also strongly activated a Na+ influx and caused cell swelling. This response was also inhibited by amiloride and DIDS but was unaffected by oxygenation. Simultaneous application of isoproterenol and hyperto...
Aquaculture, 1999
Red blood cells from rainbow trout rely mainly on oxidative phosphorylation to cover the energy demand of processes such as cation transport and protein synthesis. Stimulation of these cells with catecholamines leads to an increase in the intracellular Na q concentration due to adrenergic activation of the erythrocyte Na q -H q exchanger. Adrenergic stimulation also increases red cell oxidative phosphorylation which largely can be ascribed to increased activity of the Na q -K q pump in response to the increase in intracellular Na q concentration. Based on experiments with the Na q -ionophore, monensin, it has been suggested that adrenergic stimulation is a prerequisite for the increase in oxidative ATP-production observed when intracellular Na q is increased. Using washed red blood cells from rainbow trout, the present study examines the role for adrenergic stimulation in the metabolic response when intracellular Na q is elevated. It is Ž y8 y6
Journal of Experimental Biology
We investigated the mechanisms by which adrenergic activation of sodium/proton exchange reduces the pH gradient across the membrane of rainbow trout red cells. In untreated cells, adrenergic stimulation caused a significant increase in the proton distribution ratio ([H+]e/[H+]i) across the red cell membrane. The increase in the proton distribution ratio caused by adrenergic stimulation was inhibited by the protonophore 2,4-dinitrophenol (2,4-DNP). Thus, sodium/proton exchange displaces protons from electrochemical equilibrium. Active regulation of intracellular pH by sodium/proton exchange is possible, because the extracellular dehydration of carbonic acid to carbon dioxide is uncatalyzed. The increase in proton distribution ratio caused by adrenergic stimulation was inhibited in red cell suspensions to which extracellular carbonic anhydrase had been added before stimulation. In contrast, inhibition of intracellular carbonic anhydrase markedly increased the pH changes induced by adr...
The Journal of physiology, 1984
The addition of isoprenaline to an isotonic suspension of red blood cells of rainbow trout induces an amiloride-sensitive Na+ transport which is independent of Cl- and insensitive to 4,4'-diisothiocyano-2,2'-stilbene disulphonic acid (DIDS) and furosemide. Na+ uptake is accompanied by amiloride-sensitive H+ release. The H+ efflux is dependent upon the external Na+ concentration, the K0.5 value for Na+ being 16 mM. In the presence of DIDS, when the coupled NaCl entry (NaCl co-transport) induced by catecholamine is blocked, the results provide evidence for a linked movement of Na+ and H+, with a stoicheiometry of 1:1. Exchange of H+ for Na+ induces osmotic swelling of the cells which is due to the replacement of a bound proton by an osmotically active Na+ cation. In the absence of DIDS when the bulk of the Na+ uptake is the result of a coupled entry of Na+ and Cl-, H+ extrusion still occurs and the magnitude of acid excretion is identical to that found in DIDS-treated cells. T...
Red blood cells from rainbow trout swell in vitro in an isoosmotic medium upon {jadrenergic stimulation. This response is greater with 5.5 than with 2.5 mM extracellular K.+. The red cells also swell in vivo when the fish are stressed or infused with adrenaline. This in vivo response is blocked by the {j antagonist, propranolol. Simultaneously with the in vitro swelling the intracellular proton concentration decreases and the extracellular level increases: incubation with 5 • 10-' M adrenaline increases intracellular pH by 0.1 units, reflecting a 15% decrease in intraerythrocytic proton concentration. The increase in intracellular pH associated with adrenergic swelling will raise blood oxygen affinity in stress, offsetting detrimental effects of hypoxia and exercise on oxygen loading in the gills.
Journal of Experimental Biology
The mechanism of adrenergic swelling and associated pH changes was investigated in avian (goose) and teleost (striped bass and rainbow trout) erythrocytes. The swelling of goose red cells was probably caused by Na+/K+/Cl− co-transport and consecutive osmotic flow of water into the cell. Goose red cells swelled when exposed to isoproterenol in the presence of elevated extracellular K+, but not at physiological K+ concentrations. The swelling was quantitatively inhibited by furosemide, and by removing Cl− from the incubation medium, but was not affected by DIDS. The isoproterenol-induced swelling of fish erythrocytes may be due to loosely coupled Na+/H+ and Cl−/HCO3− exchanges. Furosemide did not completely inhibit the swelling of striped bass red cells. The cell volume increased even if K+ was completely removed from the incubation medium. In contrast, both DIDS and amiloride treatment, and the removal of Na+ from the incubation medium, inhibited the volume changes. In fish red cells...
Fish Physiology and Biochemistry, 1989
The occurrence and pH dependence (pHe 7-8) of the adrenergic red cell responses of two salmonids, trout and whitefish, and a percinid, pikeperch were studied. These are all species that live in well-oxygenated waters. The responses were compared to those of carp, which tolerates oxygen-deficient waters. The adrenergic responses of trout and whitefish red cells were pronounced. In these species red cell swelling ng, the accumulation of sodium and chloride in the cell, and the increase in red cell oxygen content at atmospheric oxygen tension were maximal at pH 7.3. In contrast, pikeperch red cells responded to 13-adrenergic stimulation only at extracellular pH 7 .1. In carp, the adrenergic response, occurring below extracellular pH 7.5, was small as compared to the two salmonids. In each case the onset of the adrenergic response coincided with the onset of the Root effect. The differences in the adrenergic responses between the two salmonids and pikeperch suggest that the occurrence of the adrenergic response is not directly related to the environmental oxygen requirements of the species, but may be linked to the activity pattern.
The adrenergic responses of carp (Cyprinus carpio) red cells: effects of PO2 and pH
Journal of Experimental Biology, 1988
Carp (Cyprinus carpio) red cells do not show beta-adrenergic responses when incubated with 10(−5) mol l-1 adrenaline at atmospheric oxygen tension and a pH value close to the in vivo resting pH (approx. 8.1). However, when either the pH or the oxygen tension of the incubation medium is decreased, the adrenergic responses appear, showing that oxygen or an oxygen-linked phenomenon has a direct influence on the response. Once present, the adrenergic red cell response is similar to that of trout: cellular water content, sodium content and intracellular pH all increase. Quantitatively the effect appears to be much smaller in carp than in trout. Adrenaline induces an increase in red cell oxygen content when the oxygen content is plotted as a function of extracellular pH. This effect coincides with the onset of the Root effect and is caused by the adrenaline-induced increase in intracellular pH, since it disappears when the oxygen content is plotted as a function of intracellular pH. The r...
Aquatic Toxicology, 1993
In the present study, the effect of TBT on the adrenergically activated Na÷/H * exchange in rainbow trout erythrocytes was investigated. TBT was found to inhibit the isoproterenol-induced efflux of protons, uptake of Na ÷ and CI-ions, and cell swelling. This indicates that TBT affects the activity of the Na÷/H ÷ exchanger. The inhibitory effect of TBT apparently depended on the haematocrit value of the red cell suspension, which may indicate that TBT distributes preferentially to cell membranes where the agent interacts with the Na÷/H ÷ exchanger.
The temperature dependence of the adrenergic Na+/H+ exchanger of trout erythrocytes
Journal of Experimental Biology, 1990
The effects of temperature upon the adrenergic N a + / H + exchange of rainbow trout erythrocytes have been studied in vitro. The initial rates of H + ejection and of increase of intracellular Na + ([Na + ],) in adrenergically stimulated cells were highly temperature-dependent, with apparent Arrhenius activation energies of 112.8±10.0 (mean±s.D., N=4) and 84.113.0kJmoP 1 (N=3), respectively. The steady-state [Na + ]j following stimulation decreased progressively with cooling, whilst the time required for [Na + ], to return to control values after removal of agonist was greatly increased. The change in intracellular pH resulting from adrenergic stimulation was reduced by cooling, such that at 4°C adrenergic responses were barely measurable. The effect of temperature upon the steadystate [Na + ], and pHi was probably caused by a disparity in the temperature dependence of the transport mechanisms that contribute to the respective steady states.