Non-bicarbonate Buffering Capacity Research Articles

Comparative Muscle Physiology of Ringed (Pusa hispida), Bearded (Erignathus barbatus), and Spotted (Phoca largha) Seals from the Bering and Chukchi Seas

The physiological properties of marine mammal skeletal muscle are foundational in defining diving and foraging capacities. Further, these parameters can be useful when assessing the behavioral flexibility of species faced with environmental change or disturbance. Herein, we define species- and age-specific muscle physiology for three ice-associated seal species experiencing Arctic warming. Specifically, we evaluated myoglobin content ([Mb]), nonbicarbonate buffering capacity (β), and fiber type profiles of a major locomotor muscle, the longissimus dorsi. Muscle samples were obtained from subsistence harvested ringed (Pusa hispida; n = 11), bearded (Erignathus barbatus; n = 41), and spotted (Phoca largha; n = 12) seals of all ages in the Bering and Chukchi Seas. Adult ringed seals had the highest [Mb] (6.67 ± 0.20 g 100 g wet tissue-1), followed by spotted (5.38 ± 0.29 g 100 g wet tissue-1) and bearded (4.55 ± 0.07 g 100 g wet tissue-1) seals. [Mb] increased with age for all species, but rates of increase differed by species. In contrast, β was similar for all species and age classes. We documented higher proportions of fast-twitch relative to slow-twitch fibers in these species, and fiber type proportions did not differ significantly with age. Adult bearded seals exhibited the greatest proportion of fast-twitch fibers (68.7 ± 1.5%), followed by ringed (59.0 ± 4.8%) and spotted (55.1 ± 2.1%) seals. Overall, our data suggest a strong link between muscle physiology, diving behavior, and life history strategies, and provide insight into the physiological capacities of these potentially vulnerable species.

Extremely Elevated Myoglobin Contents in the Pelagic Melon-Headed Whale (Peponocephala electra) after Prolonged Postnatal Maturation.

Muscle biochemistry of aquatic birds and mammals varies in accordance with swimming and diving performance, as well as with ontogeny. Similar to other odontocetes, the locomotor muscles (longissimus dorsi) of neonatal melon-headed whales (Peponocephala electra) have low myoglobin content (Mb; g Mb/100 g wet muscle mass; mean ± SE; ] and low muscle nonbicarbonate buffering capacity ( slykes; ), representing only 16% of adult Mb ( g Mb/100 g wet muscle mass; ) and 56% of adult muscle nonbicarbonate buffering capacities ( slykes; ). By the juvenile stage, Mb ( g Mb/100 g wet muscle mass; ) is still only 41% of adult levels, but nonbicarbonate buffering capacity ( slykes; ) has matured. Despite the observation that Hawaiian melon-headed whales are not deep divers or long-duration divers, their Mb rivals that found in ziphiids that forage in the bathypelagic zone and monodontids that forage under sea ice. The pelagic lifestyle of melon-headed whales likely requires sustained swimming, such that endurance training could elevate Mb in the locomotor muscle. Indeed, elevated Mb in the locomotor muscles of other pelagic odontocetes has been observed. Unlike deep-diving and Arctic-dwelling odontocetes, melon-headed whales do not achieve mature muscle characteristics before nursing. It is likely that early in life, the hydrodynamic benefits of swimming in echelon position with their mothers minimizes the endurance training of the calves that would otherwise promote rapid elevations in Mb.

Deep-water prawn Pandalus borealis displays a relatively high pH regulatory capacity in response to CO2-induced acidosis

Deep-water prawn Pandalus borealis displays a relatively high pH regulatory capacity in response to CO2-induced acidosis

The normal acid–base status of mice

Rodent models are commonly used for various physiological studies including acid-base regulation. Despite the widespread use of especially genetic modified mice, little attention have been made to characterise the normal acid-base status in these animals in order to reveal proper control values. Furthermore, several studies report blood gas values obtained in anaesthetised animals. We, therefore, decided to characterise blood CO(2) binding characteristic of mouse blood in vitro and to characterise normal acid-base status in conscious BALBc mice. In vitro CO(2) dissociation curves, performed on whole blood equilibrated to various PCO₂ levels in rotating tonometers, revealed a typical mammalian pK' (pK'=7.816-0.234 × pH (r=0.34)) and a non-bicarbonate buffer capacity (16.1 ± 2.6 slyke). To measure arterial acid-base status, small blood samples were taken from undisturbed mice with indwelling catheters in the carotid artery. In these animals, pH was 7.391 ± 0.026, plasma [HCO(3)(-)] 18.4 ± 0.83 mM, PCO₂ 30.3 ± 2.1 mm Hg and lactate concentration 4.6 ± 0.7 mM. Our study, therefore, shows that mice have an arterial pH that resembles other mammals, although arterial PCO₂ tends to be lower than in larger mammals. However, pH from arterial blood sampled from mice anaesthetised with isoflurane was significantly lower (pH 7.239 ± 0.021), while plasma [HCO(3)(-)] was 18.5 ± 1.4 mM, PCO₂ 41.9 ± 2.9 mm Hg and lactate concentration 4.48 ± 0.67 mM. Furthermore, we measured metabolism and ventilation (V(E)) in order to determine the ventilation requirements (VE/VO₂) to answer whether small mammals tend to hyperventilate. We recommend, therefore, that studies on acid-base regulation in mice should be based on samples taken for indwelling catheters rather than cardiac puncture of terminally anaesthetised mice.

Physiological effects of hypercapnia in the deep-sea bivalve Acesta excavata (Fabricius, 1779) (Bivalvia; Limidae)

The option of storing CO 2 in subsea rock formations to mitigate future increases in atmospheric CO 2 may induce problems for animals in the deep sea. In the present study the deep-sea bivalve Acesta excavata was subjected to environmental hypercapnia (pHSW 6.35, P CO 2 = 33,000 μatm) corresponding to conditions reported from natural CO 2 seeps. Effects on acid–base status and metabolic rate were related to time of exposure and subsequent recovery. During exposure there was an uncompensated drop in both hemolymph and intracellular pH. Intracellular pH returned to control values, while extracellular pH remained significantly lower during recovery. Intracellular non-bicarbonate buffering capacity of the posterior adductor muscle of hypercapnic animals was significantly lower than control values, but this was not the case for the remaining tissues analyzed. Oxygen consumption initially dropped by 60%, but then increased during the final stages of exposure, which may suggest a higher tolerance to hypercapnia than expected for a deep-living species.

Physiological responses of Daphnia pulex to acid stress

BackgroundAcidity exerts a determining influence on the composition and diversity of freshwater faunas. While the physiological implications of freshwater acidification have been intensively studied in teleost fish and crayfish, much less is known about the acid-stress physiology of ecologically important groups such as cladoceran zooplankton. This study analyzed the extracellular acid-base state and CO2 partial pressure (PCO2), circulation and ventilation, as well as the respiration rate of Daphnia pulex acclimated to acidic (pH 5.5 and 6.0) and circumneutral (pH 7.8) conditions.ResultsD. pulex had a remarkably high extracellular pH of 8.33 and extracellular PCO2 of 0.56 kPa under normal ambient conditions (pH 7.8 and normocapnia). The hemolymph had a high bicarbonate concentration of 20.9 mM and a total buffer value of 51.5 meq L-1 pH-1. Bicarbonate covered 93% of the total buffer value. Acidic conditions induced a slight acidosis (ΔpH = 0.16–0.23), a 30–65% bicarbonate loss, and elevated systemic activities (tachycardia, hyperventilation, hypermetabolism). pH 6.0 animals partly compensated the bicarbonate loss by increasing the non-bicarbonate buffer value from 2.0 to 5.1 meq L-1 pH-1. The extracellular PCO2 of pH 5.5 animals was significantly reduced to 0.33 kPa, and these animals showed the highest tolerance to a short-term exposure to severe acid stress.ConclusionChronic exposure to acidic conditions had a pervasive impact on Daphnia's physiology including acid-base balance, extracellular PCO2, circulation and ventilation, and energy metabolism. Compensatory changes in extracellular non-bicarbonate buffering capacity and the improved tolerance to severe acid stress indicated the activation of defense mechanisms which may result from gene-expression mediated adjustments in hemolymph buffer proteins and in epithelial properties. Mechanistic analyses of the interdependence between extracellular acid-base balance and CO2 transport raised the question of whether a carbonic anhydrase (CA) is involved in the catalysis of the reaction, which led to the discovery of 31 CA-genes in the genome of D. pulex.

Effect of Tris-Hydroxymethyl Aminomethane on intracellular pH depends on the extracellular non-bicarbonate buffering capacity

The effect of Tris-Hydroxymethyl Aminomethane (THAM) on intracellular pH (pHi) is unknown. We previously demonstrated that the effect of sodium bicarbonate on pHi depends on the non-bicarbonate buffering system. First, human hepatocytes from hepatocytes cell culture (HepG2) were perfused with an acidotic artificial medium containing 5-mmol/L (H5) or 30-mmol/L (H30) concentrations of 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid (HEPES), a non-bicarbonate buffer. We studied the effect of THAM on the pHi in both conditions. We repeated the same protocol using an acidotic human blood with a 5% or 40% hematocrit. The pHi was measured with the pH-sensitive fluorescent dye bis-carboxyethyl carboxy-fluorescein (BCECF). Gas analysis was performed before and during the alkaline infusion. The results showed that THAM caused an intracellular alkalization that was higher when the non-bicarbonate buffer concentration was low (0.45 +/- 0.21 and 0.22 +/- 0.14 pH units with H5 and H30, respectively). A significant relationship was found between changes in pHi and changes in PCO(2). Similar results were obtained with the human blood. In conclusion, the intracellular alkalizing effect of THAM is caused by the induced decrease of PCO(2) linked to the extracellular non-bicarbonate buffer capacity: The smaller the concentration of extracellular non-bicarbonate buffer, the higher the PCO(2) decrease caused by THAM.

Contractile properties of skeletal muscle fibre bundles from mice deficient in carbonic anhydrase II

The function of cytosolic carbonic anhydrase (CA) isozyme II is largely unknown in skeletal muscle. Because of this, we compared the in vitro contractile properties of extensor digitorum longus (EDL) and soleus (SOL) fibre bundles from mice deficient in CA II (CAD) to litter mate controls (LM). Twitch rise, 1/2 relaxation time and peak twitch force at 22 degrees C of fibre bundles from CAD EDL [28.4+/-1.4 ms, 31.2+/-2.3 ms, 6.2+/-1.0 Newton/cm(2) (N/cm(2)), respectively] and CAD SOL (54.2+/-7.5 ms, 75.7+/-13.8 ms, 2.9+/-0.5 N/cm(2), respectively) were significantly higher compared to LM EDL (20.5+/-2.2 ms, 21.9+/-3.7 ms, 4.5+/-0.2 N/cm(2)) and LM SOL (42.8+/-3.5 ms, 51.4+/-2.4 ms, 2.1+/-0.4 N/cm(2)). However, in acidic Krebs-Henseleit solution, mimicking the pH, PCO(2), and HCO(3) (-) of arterial blood from CAD mice, twitch rise, 1/2 relaxation time, and peak twitch force of fibre bundles from CAD EDL (19.3+/-0.7 ms, 19.7+/-2.3 ms, 4.8+/-0.8 N/cm(2)) and CAD SOL (41.4+/-3.6 ms, 51.9+/-5.5 ms, 2.2+/-0.7 N/cm(2)) were not significantly different from LM fibre bundles in normal Krebs-Henseleit solution (EDL: 19.7+/-1.1 ms, 21.6+/-0.6 ms, 4.7+/-0.2 N/cm(2); SOL: 42.5+/-3.1 ms, 51.8+/-2.6 ms, 1.8+/-0.3 N/cm(2)). A higher pH(i) during exposure to acidic bathing solution was maintained by CAD EDL (7.37+/-0.02) and CAD SOL (7.33+/-0.05) compared to LM EDL (7.28+/-0.04) and LM SOL (7.22+/-0.02). This suggests that the skeletal muscle of CAD mice possesses an improved defense of pH(i) against elevated pCO(2). In support of this, apparent non-bicarbonate buffer capacity (in mequiv H(+) (pH unit)(-1) (kg cell H(2)O)(-1)) as determined by pH microelectrode was markedly increased in CAD EDL (75.7+/-4.1) and CAD SOL (85.9+/-3.3) compared to LM EDL (39.3+/-4.7) and LM SOL (37.5+/-3.8). Both latter phenomena may be related to the slowed rate of intracellular acidification seen in CAD SOL in comparison with LM SOL upon an increase in PCO(2) of the bath. In conclusion, skeletal muscle from mice deficient in CA II exhibits altered handling of acid-base challenges and shows normal contractile behavior at normal intracellular pH.

Extracellular pH Defense Against Lactic Acid During And After Exercise In Females

In previous experiments with males we have found a 3 times larger extracellular nonbicarbonate buffer capacity (βnbi) for lactic acidosis during than immediately after exercise. PURPOSE To determine the magnitude of extracellular pH defense against lactic acid in female subjects and to search for mechanisms causing the exercise induced change in βnbi. METHODS pH, PCO2, [bicarbonate] and [lactate] were measured in plasma of earlobe blood during and for 21 min after exhausting incremental exercise (bicycle ergometer, + 25W every 3 min) in 18 untrained females (age 24 ± 1SE years, VO2 peak 37 ± 2 ml/min/kg). Total pH defense (−Δ[lactate/ΔpH) and □nbi ((−Δ[lactate] −Δ[bicarbonate])/ΔpH) were calculated as differences to initial rest values. Blood was also diluted 1:3 by plasma-like salt solution and titrated in vitro with lactic acid with and without addition of bicarbonate. RESULTS Total pH defense (−Δ[lactate]/ΔpH) and βnbi amounted to 98 ± 4 and 29 ± 2 mmol/l, respectively, during exercise; thereafter βnbi decreased to 11 ± 2 mmol/l which corresponds to the value usually found at rest by in vivo CO2 titration. Bicarbonate buffer capacity (βbi) was only 2 mmol/l lower after than during exercise (46 ± 1 mmol/l). In vitro βbi and βnbi amounted to 38 ± 1 and 14 ± 1 mmol/l, respectively; when only 1.5 mmol/l bicarbonate was added together with lactic acid, the values increased to 41 ± 1 and 26 ± 2 mmol/l. CONCLUSIONS The in vivo results correspond completely to those in males. There was no indication for appearance of non-bicarbonate buffers when cycling, only a small increase occured by the exerciseinduced shrinking of the extracellular volume which is rapidly reversed after exhaustion. The concomitant slight increase of [bicarbonate], however, produces a larger rise of the slope of the titration curve for total buffers than expected (as shown in the in vitro experiments), because the initial concentration is not affected. A large part of the change in βnbi during exercise is therefore only an apparent effect.

Buffering limits plasma HCO3− dehydration when red blood cell anion exchange is inhibited

Theory suggests that HCO3- dehydration in the plasma of rainbow trout is limited by both the absence of carbonic anhydrase (CA) activity and the low non-bicarbonate buffer capacity of the plasma (betaplasma). The potential for betaplasma to limit plasma HCO3- dehydration was assessed in rainbow trout in which HCO3- dehydration via the red blood cell (RBC) was inhibited using the anion exchange blocker 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS). DIDS administration reduced the rate of RBC HCO3- dehydration by 68-80% for at least 6h, resulting in the elevation of arterial CO2 tension (PaCO2) by 3.07 +/- 0.45 Torr (N = 6). Addition of bovine CA to the circulation of DIDS-treated trout caused PaCO2 to decrease significantly. This effect was increased significantly in rainbow trout in which betaplasma was elevated experimentally by intravascular injection of N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulfonic acid] (HEPES), supporting the hypothesis that CA-catalysed HCO3- dehydration in the plasma of rainbow trout is limited by proton availability.

High plasma buffering and the absence of a red blood cell β-NHE response in brown bullhead ( Ameiurus nebulosus)

The high non-bicarbonate buffer capacity of brown bullhead ( Ameiurus nebulosus) plasma was postulated to function as an alternative mechanism for the protection of red blood cell (RBC) intracellular pH (pHi) in the absence or attenuation of a RBC adrenergic response. The requirement for protecting RBC pHi arises from the presence of a Root effect haemoglobin in bullhead. In support of this hypothesis, bullhead RBCs incubated in vitro with isoproterenol (10 −8–10 −5 mol l −1) or forskolin (10 −4 mol l −1) exhibited significant cyclic AMP accumulation, but failed to exhibit cell swelling or significant Na + or Cl − accumulation; plasma pH (pHe) was also unaffected. Similarly, no significant effect on RBC water content, Na + or Cl − concentration, or pHe was detected in bullhead blood incubated with 8-bromo cyclic AMP (10 −4–10 −2 mol l −1) in vitro. These results suggest that while bullhead RBCs possess a β-adrenoreceptor linked to cyclic AMP formation, stimulation of this adrenergic receptor does not result in measurable activation of a Na +/H + exchanger.

The buffering power of plasma in brown bullhead ( Ameiurus nebulosus)

Brown bullhead ( Ameiurus nebulosus) blood plasma was found to exhibit an unusually high non-bicarbonate buffer capacity (β) in relation to that of other teleost fish. In brown bullhead, the non-bicarbonate buffer capacity of plasma (β plasma), at −5.72±0.34 mmol l −1 pH unit −1 (mean±S.E.M., N=30), constituted 37% of whole blood β and was 2.5 times higher than β plasma in rainbow trout (−2.33±0.42 mmol l −1 pH unit −1; N=7). The strong buffering power of bullhead plasma was not the result of unusually high plasma protein levels. Size separation chromatography in conjunction with a spectrophotometric assay for buffering capacity were used to isolate a plasma fraction of high buffering power. SDS-polyacrylamide gel electrophoresis revealed that this fraction contained four proteins, but was dominated by a protein of approximately 68–70 kDa molecular mass. On the basis of the amino acid composition of this fraction, the dominant protein was identified as albumin. In comparison to other fish albumins, bullhead albumin appears to be histidine-rich (6.7%). Thus, the unusually high non-bicarbonate buffer capacity of bullhead plasma appears to stem from the presence in the plasma of a histidine-rich albumin.

Extracellular pH defense against lactic acid in normoxia and hypoxia before and after a Himalayan expedition.

The extracellular pH defense against the lactic acidosis resulting from exercise can be estimated from the ratios -delta[La].delta pH-1 (where delta[La] is change in lactic acid concentration and delta pH is change in pH) and delta[HCO3-].delta pH-1 (where delta[HCO3-] is change in bicarbonate concentration) in blood plasma. The difference between -delta[La].delta pH-1 and delta[HCO3-].delta pH-1 yields the capacity of available non-bicarbonate buffers (mainly hemoglobin). In turn, delta[HCO3-].delta pH-1 can be separated into a pure bicarbonate buffering (as calculated at constant carbon dioxide tension) and a hyperventilation effect. These quantities were measured in 12 mountaineers during incremental exercise tests before, and 7-8 days (group 1) or 11-12 days (group 2) after their return from a Himalayan expedition (2800-7600 m altitude) under conditions of normoxia and acute hypoxia. In normoxia -delta[La].delta pH-1 amounted to [mean (SEM)] 92 (6) mmol.l-1 before altitude, of which 19 (4), 48 (1) and 25 (3) mmol.l-1 were due to hyperventilation, bicarbonate and non-bicarbonate buffering, respectively. After altitude -delta[La].delta pH-1 was increased to 128 (12) mmol.l-1 (P < 0.01) in group 1 and decreased to 72 (5) mmol.l-1 in group 2 (P < 0.05), resulting mainly from apparent large changes of non-bicarbonate buffer capacity, which amounted to 49 (14) mmol.l-1 in group 1 and to 10 (2) mmol.l-1 in group 2. In acute hypoxia the apparent increase in non-bicarbonate buffers of group 1 was even larger [140 (18) mmol.l-1]. Since the hemoglobin mass was only modestly elevated after descent, other factors must play a role. It is proposed here that the transport of La- and H+ across cell membranes is differently influenced by high-altitude acclimatization.

Exposure of Arenicola marina to extreme temperatures:adaptive flexibility of a boreal and a subpolar population

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 181:215-226 (1999) - doi:10.3354/meps181215 Exposure of Arenicola marina to extreme temperatures: adaptive flexibility of a boreal and a subpolar population A. Sommer, H. O. Pörtner* Alfred-Wegener-Institut für Polar- und Meeresforschung, Biologie I/ Ñkophysiologie, Columbusstrasse, D-27568 Bremerhaven, Germany *Addressee for correspondence. E-mail: hpoertner@awi-bremerhaven.de ABSTRACT: Adaptive flexibility under temperature stress was studied in a boreal and a subpolar population of Arenicola marina (L.) from the North and White Seas. Temperature stress leads to the onset of anaerobic metabolism and the ability to acclimate is interpreted to be associated with a reversal of this initial transition to anaerobiosis, restoring total aerobic conditions. Thus, end products of anaerobic metabolism as well as adenylate and ammonium concentrations were measured as indicators of temperature stress. The results reveal that the populations differ in their ability to acclimate to temperatures 4°C above their respective high critical temperature. Lugworms from the North Sea survived for only slightly longer than 1 d, while concentrations of alanopine and strombine were significantly elevated. However, adenylate and ammonium levels remained close to control values. In contrast, White Sea specimens showed drastic changes in the concentrations of anaerobic end products and ammonium, and ATP pools were depleted to levels below detection limits during the first 24 h at high temperatures. A higher metabolic proton production in White Sea worms, together with a lower intracellular non-bicarbonate buffer capacity led to a drastic drop in intracellular pH, whereas acidosis was only moderate in North Sea worms. Unexpectedly, the subpolar worms not only survived heat exposure, but even exhibited an adaptive reversal of anaerobic metabolic changes. Whereas heat exposure was compensated in White Sea worms only, the short term ability to survive cold stress (-1.7°C) is limited in summer worms from both populations. Therefore, after an initial reversal of anaerobic metabolism, concentrations of volatile fatty acids and succinate increased again after 3 d. Since White Sea worms can acclimatise to temperatures below -2°C during winter, our data suggest, that in contrast to warm acclimation, cold acclimation requires a moderate and protracted decline in temperature. KEY WORDS: Temperature adaption · Anaerobic metabolism · Arenicola marina · Heat stress · Cold stress · Adenylates · Polychaeta · Buffer capacity Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 181. Publication date: May 18, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Respiratory and metabolic responses of the Australian Yabby Cherax destructor to progressive and sustained environmental hypoxia

The Australian Yabby, Cherax destructor, inhabits occasionally hypoxic water. The respiratory gas, acid-base, metabolite and energetic status of this crayfish was assessed during progressive hypoxia and during 3 h at a water PO2 of 1.33 kPa. The O2 affinity of haemocyanin from C. destructor was increased by lactate (Δlog P50/Δlog[lactate] = −0.111) and by Ca (Δlog P50/Δlog[Ca] = −0.62) but not by urate. While the non-bicarbonate buffering capacity was low (Δ[HCO3−]/ ΔpH=−4.89) the haemocyanin had a low sensitivity to pH changes (ϕ = −0.33). The crayfish showed a compensatory hyperventilation, which induced a respiratory alkalosis, until the water O2 partial pressure declined below 2.67 kPa, after which the O2 uptake rate was approximately 10% of normoxic rates. The high haemocyanin-O2 affinity maintained haemolymph O2 content during progressive hypoxia despite the normally low arterial O2 partial pressure of C. destructor. During severe hypoxia, pH decreased but increased lactate aided in maintaining haemocyanin-O2 saturation. The importance of regulated haemocyanin-O2 affinity in hypoxic C. destructor was reduced by lowered metabolism, including reduced cardiac output, and the consequent reduction in O2 requirement. Anaerobiosis became important only at very low PO2 but thereafter proceeded rapidly, supported by a marked hyperglycaemia. There was no depletion of adenylates, even after 3 h of severe hypoxia. The tail muscle of C. destructor held small amounts of glycogen which would sustain anaerobiosis for a only a few hours. Hypometabolism seems an important hypoxic response but severe hypoxia may encourage the crayfish to breathe air.

Haemolymph oxygen transport and acid-base status in Glyptonotus antarcticus Eights

Haemolymph samples were withdrawn from routinely active male intermoult Glyptonotus held at 0 ± 0.5°C, and analysed for blood-gas and acid-base variables. In both the arterialised (a) and venous (v) haemolymph, over 50% of the oxygen was transported as dissolved oxygen at PaO2 and PvO2 levels of 12.0 ± 1.15 and 7.70 ± 1.89 kPa, respectively. The maximum oxygen-carrying capacity of the haemocyanin (CmaxHcO2) was relatively low at 0.19 ± 0.05 mmol l−1, accompanied by relatively low protein and [Cu2+] levels indicating low circulating haemocyanin concentrations. Arterialised haemolymph had a mean pH of 7.88 ± 0.02(6) at a PCO2 of 0.12 ± 0.01(6) kPa and a bicarbonate level of 12.95 ± 0.80(6) mequiv l−1 with small differences in PCO2 and pH between arterial and venous haemolymph. The non-bicarbonate buffering capacity of Glyptonotus haemolymph was low at −2.0 mequiv l−1 HCO3− pH unit−1. Haemolymph [l-lactate] and [d-glucose] levels were similar at < 1 mmol l−1 in animals held in the laboratory and those sampled in Antarctica. The blood-gas and acid-base status of Glyptonotus haemolymph may be a reflection of the low and stable temperatures experienced by this Antarctic crustacean.

The blood proteins of the Antarctic icefish Channichthys rhinoceratus: biological significance and purification of the two main components

The lack of hemoglobin and of carbonic anhydrase in the blood of icefish suggest that substantial adaptations of the acid-base balance should occur in order to ensure blood pH homeostasis. The level of peptidic histidyl and of reactive -SH groups per unit of body mass in icefish plasma are 12–13 times higher than those of Notothenia rossii, a common red-blooded Antarctic species. It is proposed that the high level of imidazole ring in icefish plasma improves the non-bicarbonate buffering capacity and that the reactive sulfhydryls are involved in a redox buffer as in some other hypoxia tolerant species. After plasma fractionation on Ultrogel AcA 34, the two main icefish serum proteins have been purified by DEAE cellulose chromatography (IFI) and by HPLC on anion exchange column (IF2). IFI has been identified as a cysteine-rich para-albumin and IF2 as an histidine-rich immunoglobulin-like protein.

Biochemical indices of aerobic and anaerobic capacity in muscle tissues of California elasmobranch fishes differing in typical activity level

Biochemical indices of aerobic and anaerobic metabolic capacity were measured in white myotomal muscle of eight marine elasmobranch fish species representing a broad range of locomotor performance, and in red myotomal muscle and heart of three of those species. The objectives were to determine if metabolic capacities vary with typical fish activity level, to compare the endothermic mako shark with ectothermic pelagic sharks, and to compare elasmobranchs with teleosts in order to test the hypothesis that elasmobranchs have lower aerobic capacities, metabolic rates, and swimming speeds. In white myotomal muscle, activities of the enzymes citrate synthase (an index of aerobic capacity), pyruvate kinase, and lactate dehydrogenase (LDH, an index of anaerobic capacity) covaried with typical activity level, and the ability to tolerate intracellular acidification (nonbicarbonate buffering capacity) corresponded with LDH activity. Enzyme activities in red muscle and heart did not show a consistent pattern with respect to fish activity. In comparison with ectothermic sharks, the mako shark had greater aerobic and anaerobic capacities in white muscle, but no significant differences were found in red muscle or heart. This pattern has also been found in teleosts. Thus, endothermic fishes elevate the temperature of red muscle, a tissue specialized for high aerobic performance, whereas white muscle biochemical characteristics are adjusted to support high rates of contraction both aerobically and anaerobically. Muscle enzymic activities of elasmobranchs and teleosts with comparable locomotor habits are similar, thus refuting the hypothesis that elasmobranchs are sluggish, with lower metabolic capacities than teleosts.

Buffer capacity of rat cortical tissue as well as of cultured neurons and astrocytes

The primary objective of this work was to assess the intrinsic nonbicarbonate buffer capacity (β i) of cultured neurons and astrocytes an d to compare the β i values obtained to those of neocortical tissue. A second objective was to determine the pH dependence of β i. Titration of homogenates of whole-brain cortical tissue and cultured neurons with NaOH and HC1 gave β i values of 25–30 mmol·1 −1·pH −1. The buffer capacity was essentially constant in the pH range of 6–7. Astrocytes showed a higher buffer capacity and a clear relationship between β i and pH. However, βini decreased when pH reduced from 7 to 6. The β i values derived from microspectrofluorometric studies on neurons and astrocytes were suprisingly variable, ranging from 10 to 50 mmol·1 −1·pH −1. The ammonia “step method” suggested that β i increased dramatically when pH was lowered from 7 to 6 but the propionic “step method” failed to reveal such a pH dependence. Some techniques obviously give erroneous values for β i, presumably because changes in buffer base concentration (due to transmembrane fluxes of H +, HCO − 3, NH 4 + or anions of weak acids) violate the principles upon which the calculations are based. From the results obtained by direct titration and with the propionate technique, we tentatively conclude that β i in neurons and astrocytes are ≈20 and 30 mmol·1 −1·pH −1, We further suggest that the term “intrinsic buffer capacity”, as commonly used, isredefined.

The Effects of Body Size on the Acid–Base and Metabolite Status in the White Muscle of Rainbow Trout Before and After Exhaustive Exercise

ABSTRACT The effect of body size on the white muscle acid–base and metabolite status was examined in rainbow trout (Oncorhynchus mykiss) ranging in length from 8 to 54cm. Following 5min of exhaustive exercise, white muscle lactate concentration was approximately doubled (approximately 32 μmol g−1) in larger fish than in smaller fish (approximately 16 μmol g−1). Associated with this post-exercise increase in lactate was a nearly parallel increase in the number of metabolic protons produced by larger fish. Larger fish did not possess a greater non-bicarbonate buffering capacity or soluble protein concentration, so their mean muscle intracellular pH (pHi) decreased by approximately 0.70 units compared with a change in mean pHi of about 0.40 units in the smallest fish. The relationship between resting pHi and length was independent of size (mean pHi7.31). Concentrations of muscle energy metabolites were also determined in trout white muscle before and after exercise. Under resting conditions, larger fish possessed a twofold greater concentration of ATP (approximately 7 μmol g−1) than did smaller fish (approximately 3μmol g−1). Similarly, resting values of muscle glycogen range from about 6 μmol g−1 in the smallest fish to as high as 15 μmol g−1 in the largest fish. However, the smaller fish had higher levels (approximately 35 μmol g−1) of phosphocreatine (PCr) than the larger fish (approximately 25 μmol g−1). Following exercise, however, both ATP and glycogen concentrations remained size-dependent and increased with increases in fish length. Levels of PCr were size-independent following exercise. These results demonstrate that body size has an important influence on the acid–base and metabolic status of fish before and after exercise.