Red Cell pH Research Articles

The Relationship Between Intracellular pH and Swimming Performance of Brown Trout Exposed to Neutral and Sublethal pH

ABSTRACT Adult brown trout were acclimated for 2–4 weeks to artificial soft water ([Ca2+] 25 μmol l−1) at neutral pH and at summer (15°C) temperature. During this period they swam against a current of approximately 0.25 ms −1. They then had their dorsal aorta cannulated and were exposed to neutral or sublethal pH (4.5) for 4 days in still water. After 4 days of exposure to sublethal pH, critical swimming speed (Ucrit) was 35% lower than that for fish at neutral pH. There were significant increases in arterial and in blood lactate concentrations at Ucrit compared with the values in resting fish at neutral pH and these led to significant reductions in plasma pH. There were no such changes in fish at sublethal pH. There were no significant changes in intracellular pH (pHi) of red blood cells at Ucrit, probably as a result of increases in the levels of plasma catecholamines. There were significant reductions in pHi of red and white muscle fibres at Ucrit. It is argued that these values were not as low in the white fibres as those seen in previous studies after fish have been chased to exhaustion and, therefore, that the fish in the present study were not completely exhausted, although they would no longer swim at a steady speed. As pHi of the red muscle was the same at Ucrit for fish at neutral and at sublethal pH, it is suggested that Ucrit (fatigue) coincides with a particular pHi of the red muscles and possible mechanisms are discussed.

Relationship between blood buffering properties, erythrocyte pH and water content, in gray seals (Halichoerus grypus).

The separated plasma of gray seals (Halichoerus grypus) has an unusually high non-bicarbonate buffering capacity (beta NB = d[HCO3-]/dpH = -21 Slykes; Slyke = mmol l-1 pH unit-1). To examine whether this represents a trait of mammalian carnivora, or is related instead to deep diving, we examined blood from dog and killer whale, respectively. The beta NB of separated plasma of dog was typically low (-4 to -8 Slykes), as in other mammals, whereas that of the whale (-13.5 Slykes), while significantly higher than dog, was not nearly as high as in seal. As one would theoretically predict of a blood system with exceptionally high extracellular buffering and functional anion exchange across the erythrocyte membrane, there was little difference in the buffer slope between true plasma and whole blood of seal. This appears to be a novel pattern of CO2 carriage in mammals. Erythrocyte ion concentrations were similar to other mammalian carnivora, with intracellular sodium concentration being high and potassium low. The red cell water content was unaffected by changes in oxygen saturation and tended to decrease when extracellular pH decreased below 7.4. Apart from the comparatively elevated Bohr factor, -0.518 as a function of extracellular pH and -0.550 as a function of red blood cell pH, the blood oxygen binding properties were similar to terrestrial mammals of similar size.

In vitro Interactions Between Oxygen and Carbon Dioxide Transport in the Blood of the Sea Lamprey (Petromyzon Marinus)

ABSTRACT In vitro experiments were carried out to examine the interactions between oxygen and carbon dioxide transport in the blood of the sea lamprey. Oxygen dissociation curves for whole blood obtained from quiescent lampreys had Hill numbers (NH) ranging from 1.52 to 1.89. The Bohr coefficient for whole blood was −0.17 when extracellular pH (pHe) was considered, but was much greater (−0.63) when red blood cell pH (pHi) was considered. The pHi was largely dependent on haemoglobin oxygen-saturation and the pH gradient across the red blood cell membrane was often reversed when was increased and/or was lowered. The magnitude of the increase in pHi associated with the Haldane effect ranged from 0.169 pH units at 2.9 kPa to 0.453 pH units at a of 0.2 kPa. Deoxygenated red blood cells had a much greater total CO2concentration than oxygenated red blood cells, but the nonbicarbonate buffer value for the red blood cells was unaffected by oxygenation. Plasma was not significantly different under oxygenated or deoxygenated conditions. Partitioning of CO2 carriage in oxygenated and deoxygenated blood supports recent in vivo observations that red blood cell CO2 carriage can account for much of the difference between arterial and venous blood. Together, the results also suggest that oxygen and carbon dioxide transport may not be tightly coupled in the blood of these primitive vertebrates. Finally, red cell sodium concentrations were dependent on oxygen and carbon dioxide tensions in the blood, suggesting that sodium-dependent ion transport processes may contribute to the unique strategy for gas transport in sea lamprey blood.

Abbreviated laparotomy and planned reoperation for critically injured patients.

The triad of hypothermia, acidosis, and coagulopathy in critically injured patients is a vicious cycle that, if uninterrupted, is rapidly fatal. During the past 7.5 years, 200 patients were treated with unorthodox techniques to abruptly terminate the laparotomy and break the cycle. One hundred seventy patients (85%) suffered penetrating injuries and 30 (15%) were victims of blunt trauma. The mean Revised Trauma Score, Injury Severity Score, and Trauma Index Severity Score age combination index predicted survival were 5.06%, 33.2%, and 57%, respectively. Resuscitative thoracotomies were performed in 60 (30%) patients. After major sources of hemorrhage were controlled, the following clinical and laboratory mean values were observed: red cell transfusions--22 units, core temperature--32.1 C, and pH--7.09. Techniques to abbreviate the operation included the ligation of enteric injuries in 34 patients, retained vascular clamps in 13, temporary intravascular shunts in four, packing of diffusely bleeding surfaces in 171, and the use of multiple towel clips to close only the skin of the abdominal wall in 178. Patients then were transported to the surgical intensive care unit for vigorous correction of metabolic derangements and coagulopathies. Ninety-eight patients (49%) survived to undergo planned reoperation (mean delay 48.1 hours), and 66 of 98 (67%) survived to leave the hospital. With the exception of intravascular shunts, there were survivors who were treated by each of the unorthodox techniques. Of 102 patients who died before reoperation 68 (67%) did so within 2 hours of the initial procedure. Logistic regression showed that red cell transfusion rate and pH may be helpful in determining when to consider abbreviated laparotomy. The authors conclude that patients with hypothermia, acidosis, and coagulopathy are at high risk for imminent death, and that prompt termination of laparotomy with the use of the above techniques is a rational approach to an apparently hopeless situation.

Effects of oxygen saturation on the CO2 transport properties of Lampetra red cells.

We investigated the effects of haemoglobin oxygenation on the carbon dioxide transport properties of lamprey (Lampetra fluviatilis) erythrocytes. The non-bicarbonate buffering capacity of deoxygenated lamprey erythrocytes was -43 mmol.L-1.pH unit-1. The carbon dioxide content of oxygenated erythrocytes was 7-8 mM lower than that of deoxygenated erythrocytes over a range of carbon dioxide tensions. This was the result of a pronounced Haldane effect (proton uptake by haemoglobin upon deoxygenation): at extracellular pH 7.5, the intracellular pH of oxygenated erythrocytes was 7.67, and increased to 7.91 when the haemoglobin-oxygen saturation decreased to 7%. No specific oxylabile binding of bicarbonate or carbon dioxide to haemoglobin occurred under the conditions of the present study. Owing to the high red cell pH and its large increase upon deoxygenation, carbon dioxide can be effectively transported in lamprey blood, although plasma bicarbonate is not available for carbon dioxide excretion because of the lack of rapid anion exchange across the red cell membrane.

Adrenergic Control of Red Cell pH in Salmonid Fish: Roles of the Sodium/Proton Exchange, Jacobs-Stewart Cycle and Membrane Potential

ABSTRACT 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 adrenergic stimulation, suggesting that the net direction of the intracellular hydration/dehydration reaction may markedly affect the intracellular pH changes. Membrane potential changes are not a necessary component of the adrenergic response. The increases in red cell volume and sodium and chloride concentrations induced by adrenergic stimulation were unaffected in cells ‘voltage-clamped’ by valinomycin.

Nitrite and Red Cell Function in Carp: Control Factors for Nitrite Entry, Membrane Potassium Ion Permeation, Oxygen Affinity and Methaemoglobin Formation

ABSTRACT Red cell function was studied in carp by a combination of in vivo and in vitro experiments with nitrite as the perturbing agent. In vivo accumulation of nitrite caused a marked increase in the red cell methaemoglobin content, and reduced the mean cellular volume. The oxygen affinity of unoxidized haemoglobin was strongly decreased, partly as result of the elevated concentration of cellular nucleoside triphosphates and haemoglobin associated with red cell shrinkage. Red cell pH was unchanged compared to controls, but reduced when referred to constant extracellular pH and O2 saturation. The mean cellular K+ content decreased, reflecting a K+ loss from the red cells during their shrinkage. This K+ loss contributed significantly to the large plasma hyperkalaemia during nitrite exposure. In vitro experiments revealed that nitrite influx into deoxygenated red cells was much larger than into oxygenated red cells. Nitrite permeation of the red cell membrane was not inhibited by DIDS and did not change extracellular pH. Methaemoglobin (MetHb) formation was more pronounced in deoxygenated blood than in oxygenated blood, but quasi-steady states were reached, reflecting a balance between nitrite-induced MetHb formation and the action of MetHb reductase. Red cells incubated in the oxygenated state released K+, whereas a net K+ uptake occurred in deoxygenated cells. Nitrite did not change the K+ loss from oxygenated cells, but shifted the K+ uptake in deoxygenated cells to a pronounced K+ release by the time high MetHb levels were reached. Both types of red cell K+ release were inhibited by DIDS and appeared to occur via a route involving Band 3. The data are consistent with the hypothesis that a significant DIDS-sensitive K+ efflux from the red cells occurs whenever a large fraction of the haemoglobin molecules assumes an R-like quaternary structure.

A three-state MWC analysis of oxygenation in tench (Tinca tinca) hemoglobin

Oxygen equilibria in tench hemoglobin were analysed according to a three-state MWC model. In addition to theT andR states of the traditionally used two-state model, the three-state model introduces an additional state, theS state, when organic phosphates bind to theT-structure hemoglobin. Under conditions covering natural red cell pH values and nucleoside triphosphate-hemoglobin ratios, it was possible to closely fit experimental data to the three-state equation with constant values of the association constantsKR,KT, andKS, and with only the allosteric constantsL andM varying with effector conditions. Thus, in contrast to a twostate analysis of oxygen equilibria, the three-state analysis was consistent with the basic assumption of the MWC model, that heterotropic ligands only affect allosteric constants and not association constants. The temperature-dependence of the three-state parameter values showed that in the presence of nucleoside triphosphate the dominance of theS state over theT state was most pronounced at low temperatures. Furthermore, the numerical values of the enthalpy and entropy change of oxygenation were lower in theS state than in theT andR states, and the enthalpy and entropy change for the allostericS→R transition were much larger than for theT→R transition.

Absence of adrenergic red cell pH and oxygen content regulation in American eel (Anguilla rostrata) during hypercapnic acidosis in vivo and in vitro

American eels (Anguilla rostrata) were exposed to acute (30 min) external hypercapnia (1% CO2 or 5% CO2 in air) in order to assess the involvement of circulating catecholamines in regulating red blood cell (RBC) pH and oxygen content during whole blood acidosis. Plasma adrenaline levels increased approximately 5-fold during severe hypercapnia yet absolute levels remained below 1.0 nM; plasma noradrenaline levels were unchanged. Both RBC pH and oxygen bound to haemoglobin ([O2]/[Hb]) conformed to in vitro relationships with whole blood pH (pHe) indicating absence of regulation during hypercapnia in vivo. Pre-treatment of eels with α- or β-adrenoceptor antagonists, phentolamine or propranolol was without effect on RBC pH or [O2]/[Hb] during hypercapnia. Further, intra-arterial injection of adrenaline (final plasma concentration=134 nM) or noradrenaline (final plasma concentration = 34 nM) into hypercapnic eels 5 min prior to blood sampling did not modify any measured blood variable RBC nucleoside triphosphate (NTP) levels, RBC pH and [O2]/[Hb]. In vitro, the application of adrenaline or noradrenaline to eel RBC's during graded normoxic hypercapnia or hypoxic hypercapnia (noradrenaline only) did not affect RBC pH significantly. RBC NTP levels were depressed by noradrenaline in vitro but only during hypoxic hypercapnia.

Metabolic dynamics in the human red cell: Part II—Interactions with the environment

The maintenance of human red cell volume under multitude of trying physiological conditions is a self regulated dynamic process. Theoretical and experimental studies on red cell osmotic states have been primarily focussed on three different interdependent areas: the permeative properties of the red cell membrane, the kinetic studies of transmembrane fluxes of various ionic and nonionic chemical constituents of the red cell and plasma, and the ideal and non-ideal thermodynamic formulation of the osmotic states. The primary objective of this work is to provide a general model that converges the above mentioned components of the red cell and its environment under one umbrella. Such a model facilitates the simultaneous interpretation and prediction of quantitative changes in the red cell volume, pH, Donnan ratios, osmotic effects, plasma volume, transmembrane fluxes, and permeable and impermeable solute concentration.

Regulation of acid and ion transfer across the membrane of nucleated erythrocytes

The major pathways for proton transport across the membrane of nucleated erythrocytes are the passive Jacobs–Stewart cycle and the secondarily active sodium–proton exchange. The relative importance of these two pathways in the control of red cell pH depends on the sodium–proton exchange rate and the rate of the slowest step of passive proton equilibration. In cyclostome red cells, which lack anion exchange, intracellular pH is controlled by the sodium-dependent acid–extrusion mechanism. In unstimulated teleost red cells, the Jacobs–Stewart cycle appears to be the most important pathway for the transport of protons across the membrane. Adrenergic stimulation activates sodium–proton exchange. Sodium–proton exchange is able to increase intracellular pH and decrease extracellular pH because the rate of proton transport via the Jacobs–Stewart cycle is limited by the uncatalysed extracellular dehydration of carbonic acid to carbon dioxide. The turnover rate of the adrenergically activated sodium–proton exchange is influenced by pH and oxygen tension. In amphibian red cells, acidification activates sodium–proton exchange. The exchange may limit the changes in intracellular pH after acid–base disturbances.

The role of catecholamines in regulating arterial oxygen content during acute hypercapnic acidosis in rainbow trout ( Salmo gairdneri)

The involvement of catecholamines in regulating arterial oxygen content (Ca O 2 ) during hypercapnic acidosis in rainbow trout ( Salmo gairdneri) was investigated by comparing physiological responses during acute normoxic hypercapnia (a condition in which plasma epinephrine is elevated) and acute hyperoxic hypercapnia (a condition in which plasma epinephrine is not elevated). Red blood cell pH (rbc pH) was maintained significantly higher in the normoxic hypercapnic fish despite similar reductions in whole blood pH (pHe) in both groups. Elevation of rbc pH in the normoxic hypercanic fish was abolished by pre-treatment with the β-adrenoceptor antagonist, propranolol, whereas injection of epinephrine into hyperoxic hypercapnic fish significantly raised rbc pH. Arterial blood oxygen carrying capacity increased only in the normoxic hypercapnic fish due to significant increases in blood haemoglobin (Hb) levels. The ability in trout to elevate blood Hb was abolished by pre-treatment with the α-adrenoceptor antagonist, phentolamine. Injections of epinephrine into normacapnic fish caused increases in blood Hb and concomitant decreases in spleen wet weight and Hb content. Adrenergic elevation of blood Hb was not observed in splenectomized fish. Ca O 2 , although depressed during normoxic hypercapnia, was indeed regulated when compared to Ca O 2 values predicted from the in vitro Root effect. Pre-treatment with phentolamine, but not propranolol, abolished the ability of trout to regulate Ca O 2 .

The Effects of Hypersaline Exposure on Oxygen-Affinity of the Blood of the Freshwater Teleost Catostomus Commersoni

ABSTRACT After 10 days’ exposure to an environmental salinity of 300mosmol kg−1 NaCl, the freshwater stenohaline teleost Catostomus commersoni exhibited an increase in plasma osmolality and a reduction in plasma strong ion difference (SID). There were reductions in plasma pH (pHe), red blood cell (RBC) pH (pHi), plasma total CO2 and erythrocyte nucleoside triphosphate (NTP) concentration, and increases in mean erythrocyte volume and plasma catecholamine levels. Despite the acidosis, the in vitro haemoglobin oxygen-affinity of blood from saline-acclimated fish was not significantly different from that of control fish (held in fresh water) which had higher pHe and pHi values at the tensions used. In vitro adjustment of SID of blood from control fish to approximate that of the saline-acclimated fish by the addition of NaOH and HC1 significantly reduced pHe, pHi and the haemoglobin oxygen-affinity. Adjustment of the plasma osmolality of blood from control fish to values identical to those of the saline-acclimated fish by the addition of NaCl in vitro did not alter the haemoglobin oxygen-affinity. An increase in catecholamine concentration and a decrease in red blood cell N IP concentration in the saline-acclimated fish may have been compensatory mechanisms to maintain haemoglobin oxygen-affinity against acidosis-induced Bohr and Root effects during saline exposure.

The Distribution of Ammonia and H+ Between Tissue Compartments in Lemon Sole (Parophrys Vetulus) at Rest, During Hypercapnia and Following Exercise

ABSTRACT The distribution of ammonia and [146C]DMO was compared in white muscle, heart, brain, red cells and plasma of lemon sole (Parophrys vetulus Girard) at rest, during hypercapnia and following strenuous exercise. In red cells at rest, measured intracellular ammonia levels were equal to those predicted by the plasma to red cell pH gradient. Red cells are unusual in that hydrogen ions are passively distributed according to membrane potential (EM), whereas in other tissues this is not the case. In white muscle, heart and brain under all experimental conditions, intracellular ammonia levels far exceed those predicted by transmembrane pH gradients. Calculated values in these tissues are very close to published resting values of EM. We conclude that, in lemon sole, NH4+ permeates cell membranes and that intracellular ammonia stores are not determined by transmembrane pH gradients.

Acute exposure to graded levels of hypoxia in rainbow trout ( Salmo gairdneri): metabolic and respiratory adaptations

We have studied the mechanisms of acute hypoxia tolerance in rainbow trout ( Salmo gairdneri). Fish held at 9°C were exposed to various levels of hypoxia for 24 h. At an environmental P O 2 of 30 Torr, the fish showed an initial plasma acidosis probably of metabolic origin which was subsequently offset such that blood pH returned to normal within about 4h. Over this time period, red cell pH was maintained constant. Comparing the effects of different levels of hypoxia following 24 h exposure, oxygen consumption of the animal remained unchanged over a broad range of inspired oxygen tensions but declined by over 30% of normoxic values at inspired water P O 2 levels of 80 Torr. This appeared to be a true metabolic depression becaused signs of increased anaerobic metabolism did not occur until there was a further reduction in water oxygen levels. Rainbow trout appear to be able to maintain a relatively high energy status in their white muscle during 24 h exposure to severe hypoxia (water P O 2 = 30 Torr). As the level of hypoxia was intensified, there was a reduction in the oxygen gradient across the gills, probably facilitated in part by the release of catecholamines into the blood. The erythrocytic ATP:Hb 4 molar ratios declined with increasing hypoxic stress as did the pH gradient between the erythrocyte and plasma. The overall effect was no change in Hb O 2-affinity after 24 h exposure to severe hypoxia.

Adrenergic involvement in blood oxygen transport and acid-base balance during hypercapnic acidosis in the Rainbow Trout,Salmo gairdneri

Rainbow trout (Salmo gairdneri) were subjected to 12 h of external hypercapnia (1% CO2 in air) during α- and/or β-adrenoceptor blockade in order to assess the importance of adrenergic responses in modulating blood oxygen transport and acid-base balance during an acute acidotic stress. External hypercapnia caused an elevation of blood carbon dioxide tension and a reciprocal decrease in whole blood pH. A gradual elevation of blood bicarbonate levels caused whole blood pH to increase toward pre-hypercapnic values throughout the hypercapnic period. Pre-treatment of fish with propranolol (a β-adrenoceptor antagonist) or phentolamine (an α-adrenoceptor antagonist) did not affect their ability to regulate extracellular acid-base status during hypercapnia. On the other hand, adrenergic responses were essential in the maintenance of arterial blood oxygen content during hypercapnia despite the severe extracellular acidosis and a marked Root effect in trout blood, in vitro. Important adrenergic responses included pronounced increases in haematocrit (an α-adrenergic effect) and arterial oxygen tension (α- and β-adrenergic effects) as well as partial regulation of red blood cell pH (a β-adrenergic effect). Although pre-treatment of fish with either propranolol or phentolamine caused a reduction in blood oxygen content during hypercapnia, fish died only during complete adrenoceptor blockade, presumably due to severe hypoxemia.

Effects of prolonged epinephrine infusion on blood respiratory and acid-base states in the rainbow trout: Alpha and beta effects

Rainbow trout were infused continuously for 12h with epinephrine in the presence or absence of alpha-and/or beta-adrenergic blockade to characterize the specific adrenergic mechanisms involved in the control of blood acid-base status and oxygen transport capacity. Infusion of epinephrine, alone, produced a transient respiratory acidosis, as indicated by an increase in carbon dioxide tension and a decrease in whole blood pH, yet arterial oxygen tension was elevated. Red blood cell pH increased by approximately 0.2 pH units during epinephrine infusion and this increase as well as the increase in oxygen tension were prevented by pretreatment with propranolol (a beta-adrenergic antagonist). Epinephrine infusion during alpha-adrenergic blockade caused a prolonged elevation of blood carbon dioxide tension and abolished the increases in hematocrit and hemoglobin concentrations observed during epinephrine infusion alone. Infusion of the alpha-adrenergic agonists phenylephrine (an alpha1 agonist) or clonidine (an alpha2 agonist) caused respiratory acidosis (decreased pH, increased CO2 tension) and a reduction in oxygen tension. Infusion of isoprenaline (a non-specific beta agonist) caused delayed increases in carbon dioxide and oxygen tensions. We speculate that the increased carbon dioxide tension observed during epinephrine infusion is a result of beta-adrenoceptor mediated inhibition of red blood cell bicarbonate dehydration and not branchial convective or diffusive adjustments. The effects of epinephrine on blood O2 tension, content and carrying capacity are discussed with reference to the participation of alpha- and beta-adrenergic mechanisms at the gill, spleen and red blood cell.

Acid-base regulation following acute acidosis in seawater-adapted rainbow trout, Salmo gairdneri: a possible role for catecholamines.

A fall in blood pH was induced by intra-arterial infusion of HCl in seawater-adapted rainbow trout (Salmo gairdneri). The acute acidosis resulting from HCl infusion caused a short-lived decrease in plasma bicarbonate concentration ([HCO3-]) and an increase in arterial CO2 tension (PaCO2). Erythrocyte pH and bicarbonate concentrations were not significantly altered by the infusion of acid. Injection of acid did, however, stimulate a branchial net H+ efflux which could be primarily accounted for by a net uptake of bicarbonate equivalent ions from the environmental water. Acid infusion of animals pre-treated with the beta-adrenergic blocking agent, propranolol, induced a similar pattern of change in plasma acid-base status. However, the recovery of plasma pH and restoration of plasma [HCO3-] were slower than in animals infused with acid alone. Red cell pH fell significantly in the face of plasma acidosis in the beta-blocked animals. Erythrocyte [HCO3-] showed a similar pattern of change to that of erythrocyte pH. Branchial net H+ efflux increased to a lesser extent following acid infusion in animals treated with propranolol. We conclude that catecholamines released into the bloodstream during periods of acute acidosis may play an important role in facilitating branchial H+ efflux in seawater-adapted rainbow trout.

Effect of burst swimming and adrenaline infusion on O2 consumption and CO2 excretion in rainbow trout, Salmo gairdneri

1. Immediately following burst swimming, the oxygen consumption of rainbow trout increased by 71%, carbon dioxide excretion by 104% and the respiratory exchange ratio by 17%. 80 min after burst swimming all of these parameters had returned to levels which were not significantly different from control values. 2. Infusion of adrenaline into resting fish had no significant effect on oxygen consumption or carbon dioxide excretion and therefore there was no significant change in the respiratory exchange ratio. 3. This infusion of adrenaline caused a significant elevation in the red blood cell pH which was still present 80 min later. 4. The present results contrast with those of van den Thillart, Randall & Lin (1983), who demonstrated carbon dioxide retention after burst swimming. While it is possible that catecholamines may inhibit bicarbonate flux through the red blood cell, our experiments indicate that this inhibition would not result in detectable changes in carbon dioxide excretion or, therefore, in the respiratory exchange ratio.

Control of red cell volume and pH in trout: Effects of isoproterenol, transport inhibitors, and extracellular pH in bicarbonate/carbon dioxide‐buffered media

AbstractThe effects of extracellular pH and beta‐adrenergic stimula‐tion on the volume and pH of rainbow. trout red cells were studied in HCO3−/ CO2 butfered media. A decrease in extracellular pH caused an increase in red cell volume and a decrease in intracellular pH. The pH‐induced changes in cell volume were inhibited by 4,4′‐Diisothiocyanostilbene‐2,2′‐Disulfonic acid, (DIDS), an inhibitor of the anion exchange pathway, but not by amiloride, an inhibitor of Na+/H+ exchange, indicating that these volume changes are mainly associated with movements of chloride across the red cell membrane, and that the Na+/H+ exchanger is not activated by changes in intracellular pH alone. The adrenergic drug, isoproterenol, promoted cell swelling and proton extrusion even in the presence of 10 mM HCO3−, showing that the adrenergic response plays a significant role in the control of cytoplasmic pH. These responses were enhanced by a decrease in extracellular pH, showing that the adrenergic response is of benefit to stressed animals. DIDS markedly enhanced the effect of isoproterenol on the pHi, but abolished the increase in red cell volume. The effects of furosemide were similar to those of DIDS, suggesting that these transport inhibitors have a similar mode of action. Amiloride, on the other hand, inhibited both the volume and the pH changes associated with adrenergic stimulation. These observations support the double Na+/H+ and HCO3−/CI− exchange model of adrenergic swelling in fish red cells.