Non-bicarbonate Buffer Research Articles

A mathematical model of rat collecting duct. II. Effect of buffer delivery on urinary acidification.

A mathematical model of the rat collecting duct (CD) is used to examine the effect of delivered load of bicarbonate and nonbicarbonate buffer on urinary acidification. Increasing the delivered load of HCO(3)(-) produces bicarbonaturia, and, with luminal carbonic anhydrase absent, induces a disequilibrium luminal pH and a postequilibration increase in urinary PCO2. At baseline flows, this disequilibrium disappears when luminal carbonic anhydrase rate coefficients reach 1% of full catalysis. The magnitude of the equilibration PCO2 depends on the product of urinary acid phosphate concentration and the disequilibrium pH. Thus, although increasing phosphate delivery to the CD decreases the disequilibrium pH, the increase in urinary phosphate concentration yields an overall increase in postequilibration PCO2. In simulations of experimental HCO(3)(-) loading in the rat, model predictions of urinary PCO2 exceed the measured PCO2 of bladder urine. In part, the higher model predictions for urinary PCO2 may reflect higher urinary flow rates and lower urinary phosphate concentrations in the experimental preparations. However, when simulation of CD function during HCO(3)(-) loading acknowledges the high ambient renal medullary PCO2 (5), the predicted urinary PCO2 of the model CD is yet that much greater. This discrepancy cannot be resolved within the model but requires additional experimental data, namely, concomitant determination of urinary buffer concentrations within the tubule fluid sampled for PCO2 and pH. This model should provide a means for simulating formal testing of urinary acidification and thus for examining hypotheses regarding transport defects underlying distal renal tubular acidosis.

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.

Mechanisms of oesophageal mucosal defence

The integrity of the oesophageal mucosa depends upon an equilibrium between aggressive factors, predominantly acid and pepsin, and protective mechanisms. Protective mechanisms operate within the oesophageal mucosa as pre-epithelial, epithelial and post-epithelial defences. Only the protective components of the oesophageal pre-epithelial defence can be tested in vivo in humans. It has been recently demonstrated that human oesophageal submucosal glands elaborate mucous secretion rich in bicarbonate and non-bicarbonate buffers, mucin, prostaglandin E2, epidermal growth factor (EGF) and transforming growth factor α (TGFα). This oesophageal secretion, accompanied by similarly protective factors within the swallowed saliva, defines the protective potential of the oesophageal pre-epithelial defence that exists in the form of a mucus-buffer layer covering the oesophageal mucosa and which retards the back-diffusion of hydrogen ions. It has also been demonstrated that patients with severe erosive reflux oesophagitis exhibit qualitative impairment in both the salivary and oesophageal components of the oesophageal pre-epithelial defence. Furthermore, patients with endoscopically negative gastro-oesophageal reflux disease have a significantly stronger oesophageal pre-epithelial defence than patients with erosive reflux oesophagitis. On the other hand, African–Americans, who are less likely to develop erosive reflux oesophagitis, have a stronger oesophageal pre-epithelial defence than do Caucasians. The salivary component of the oesophageal pre-epithelial defence can be enhanced by mastication and the administration of cisapride, whereas oesophageal secretion can only be significantly augmented by cisapride.

The potential role of the esophageal pre-epithelial barrier components in the maintenance of integrity of the esophageal mucosa in patients with endoscopically negative gastroesophageal reflux disease

OBJECTIVE: Patients with gastroesophageal reflux disease (GERD) accompanied by erosive reflux esophagitis (RE) exhibit an impairment within the esophageal pre-epithelial barrier protective components that may facilitate the development and/or progression of the mucosal injury. Little is known, however, whether such impairment is a general phenomenon affecting all patients with GERD or whether this is a characteristic feature only of patients with erosive RE. We therefore studied the rate of secretion of esophageal inorganic and organic protective factors in patients with endoscopically negative [E (−)] GERD and compared these results with the corresponding values in asymptomatic volunteers (CTRL). METHODS: The study was conducted on 33 white asymptomatic volunteers and 10 white patients with a long history of GERD confirmed by 24-h pH monitoring and a grossly negative upper endoscopy. Esophageal secretion was collected during mucosal exposure to NaCl, HCl, HC/pepsin and NaCl using the esophageal perfusion catheter. In collected samples all investigated parameters were measured. RESULTS: The pH of esophageal secretion and its content of bicarbonate, EGF, and PGE 2 in patients with E (−) GERD and asymptomatic volunteers were similar. Unexpectedly, the rate of esophageal glycoconjugate (predominantly mucin) secretion was significantly higher in patients with E (−) GERD than in controls during perfusion with HCl ( p < 0.05). Furthermore, secretion of protein in patients with E (−) GERD was significantly higher than in the control group during the mucosal exposure to HCl/Pepsin ( p < 0.05). The nonbicarbonate buffer secretion during perfusion with HCl and HCl/Pepsin as well as the rate of esophageal TGFα output during infusion of final saline in patients with E (−) GERD were significantly lower than in CTRL group ( p < 0.05). CONCLUSIONS: Our data indicate that patients with E (−) GERD have an esophageal secretory potential, in terms of glycoconjugate and protein, higher than that in asymptomatic controls. This phenomenon in patients with E (−) GERD may, by enhancing the quantity of the esophageal pre-epithelial barrier, help to prevent the development of erosive esophagitis. A significantly lower esophageal secretory response in patients with E (−) GERD in terms of nonbicarbonate buffers and TGFα may facilitate the development of GERD symptoms and histological changes of GERD, respectively.

The potential role of the esophageal pre-epithelial barrier components in the maintenance of integrity of the esophageal mucosa in patients with endoscopically negative gastroesophageal reflux disease.

Patients with gastroesophageal reflux disease (GERD) accompanied by erosive reflux esophagitis (RE) exhibit an impairment within the esophageal pre-epithelial barrier protective components that may facilitate the development and/or progression of the mucosal injury. Little is known, however, whether such impairment is a general phenomenon affecting all patients with GERD or whether this is a characteristic feature only of patients with erosive RE. We therefore studied the rate of secretion of esophageal inorganic and organic protective factors in patients with endoscopically negative [E (-)] GERD and compared these results with the corresponding values in asymptomatic volunteers (CTRL). The study was conducted on 33 white asymptomatic volunteers and 10 white patients with a long history of GERD confirmed by 24-h pH monitoring and a grossly negative upper endoscopy. Esophageal secretion was collected during mucosal exposure to NaCl, HCl, HC/pepsin and NaCl using the esophageal perfusion catheter. In collected samples all investigated parameters were measured. The pH of esophageal secretion and its content of bicarbonate, EGF, and PGE2 in patients with E (-) GERD and asymptomatic volunteers were similar. Unexpectedly, the rate of esophageal glycoconjugate (predominantly mucin) secretion was significantly higher in patients with E (-) GERD than in controls during perfusion with HCl (p < 0.05). Furthermore, secretion of protein in patients with E (-) GERD was significantly higher than in the control group during the mucosal exposure to HCl/Pepsin (p < 0.05). The nonbicarbonate buffer secretion during perfusion with HCl and HCl/Pepsin as well as the rate of esophageal TGFalpha output during infusion of final saline in patients with E (-) GERD were significantly lower than in CTRL group (p < 0.05). Our data indicate that patients with E (-) GERD have an esophageal secretory potential, in terms of glycoconjugate and protein, higher than that in asymptomatic controls. This phenomenon in patients with E (-) GERD may, by enhancing the quantity of the esophageal pre-epithelial barrier, help to prevent the development of erosive esophagitis. A significantly lower esophageal secretory response in patients with E (-) GERD in terms of nonbicarbonate buffers and TGFalpha may facilitate the development of GERD symptoms and histological changes of GERD, respectively.

The increase in CO2 production induced by NaHCO3 depends on blood albumin and hemoglobin concentrations.

To evaluate the origin of H+ ions participating in the generation of CO2 coming from sodium bicarbonate infusion during metabolic acidosis. We hypothesized that these H+ ions come from a back-titration of the main non-bicarbonate buffers present in the blood, i. e. the hemoglobin and the albumin, and thus postulated that the rate of CO2 release from a bicarbonate load is dependent on the concentration of these buffers. Prospective clinical and experimental study. Surgical intensive care unit of a university hospital. (1) Sixteen stable sedated and artificially ventilated critically ill patients with a mild base deficit. (2) Acidotic human blood (bicarbonate 5 mM, pH 7.0) of hematocrit 5, 10, 20 and 40% regenerated from a mixture of frozen fresh plasma and packed red blood cells. infusion of 1.5 mmol/kg sodium bicarbonate over 5 min. Regenerated blood: 25 mM sodium bicarbonate load. continuous measurement of CO2 production (VCO2) on the expired gas using a metabolic monitor and arterial blood gas analysis before (T0), at the end (T5) and at 10, 30 and 60 min after the beginning of the bicarbonate infusion. The increase in VCO2 was 18 +/- 7% leading to a rise in PaCO2 from 39.6 +/- 2.3 at T0 to 46.2 +/- 2.7 mmHg at T5. The increases in VCO2 and in PaCO2 were significantly correlated to the albumin (r = 0.73, p < 0.005 and r = 0.70, p < 0.005, respectively) and to the hemoglobin (r = 0.51, p < 0.05 and r = 0.65, p < 0.01, respectively) concentrations. Regenerated blood: gas analysis 1 min after the bicarbonate load. The increase in PCO2 was closely related to the hematocrit (Ht) of the blood as it was 15.9 +/- 7.5 mmHg for Ht 5%, 29.0 +/- 9.6 for Ht 10%, 44.2 +/- 5.9 for Ht 20% and 71.0 +/- 3.5 for Ht 40% (n = 5 for each, p < 0.001). The importance of the release of CO2 from a bicarbonate load is dependent on the concentration of the blood non-bicarbonate buffers. It is therefore likely that the adverse effects of bicarbonate therapy linked to the CO2 generation are more important in patients with high blood albumin and hemoglobin concentrations.

Carbon dioxide storage and nonbicarbonate buffering in the human body before and after an Himalayan expedition.

Before and 7-12 days after an Himalayan expedition CO2 equilibration curves were determined in the blood plasma of 12 mountaineers by in vitro and in vivo CO2 titration; in vivo osmolality changes (delta Osm x deltaPCO2(-1), deltaOsm x delta pH(-1), where PCO2 is the partial pressure of CO2) during the latter experiments yielded estimates of whole body CO2 storage. In vitro -delta[HCO3-] x delta pH(-1) [nonbicarbonate buffer capacity (beta) of blood] was increased 7 days after descent [before 31.3 (SEM 0.4) mmol x kgH2O(-1), after 38.3 (SEM 3.9) mmol x kgH2O(-1); P<0.05] resulting from an increased proportion of young erythrocytes; in additional experiments an augmented beta was found in young (low density cells) compared to old cells [<1.097 g x ml(-1): 0.216 (SEM 0.028) mmol x gHb(-1), >1.100 g x ml(-1): 0.145 (SEM 0.013) mmol x gHb(-1), where Hb is haemoglobin; P < 0.02]. In spite of increased Hb mass in vivo delta[CO2total] x deltaPCO2(-1) [0.192 (SEM 0.010) mmol x kgH2O(-1) x mmHg(-1)] and -delta[HCO3-] x delta pH(-1) [17.9 (SEM 1.0) mmol x kgH2O(-1)] as indicators of extracellular beta rose only slightly after altitude (7 days +16%, P<0.02; +7%, NS) because of haemodilution. The deltaOsm x deltaPCO2(-1) [0.230 (SEM 0.015) mosmol x kgH2O(-1) x mmHg(-1)] remained unchanged. Prealtitude differences in deltaOsm x delta pH(-1) between hypercapnia [-41 (SEM 5) mosmol x kgH2O(-1)] and hypocapnia [-20 (SEM 3) mosmol x kgH2O(-1); P<0.01] disappeared temporarily after return since the former slope was reduced. The high value during hypercapnia before ascent probably resulted from mechanisms stabilizing intracellular pH during moderate hypercapnia which were attenuated after descent.

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.

Gastrointestinal Monitoring Using Measurement of Intramucosal PCO2

Gastrointestinal Monitoring Using Measurement of Intramucosal PCO2

BUFFERING AND RESPIRATORY COMPENSATION OF LACTIC ACIDOSIS AFTER THE WINGATE TEST

742 The “pH-defense” in the extracellular space after rapid addition of lactic acid by performing 30 s anaerobic exercise was studied in 13 subjects. Acid-base status and lactate concentration in earlobe blood were determined before and up to 30 min after the test. After this time [lactate] was still increased and pH as well as pCO2 decreased.-Δ[lactate]plasma/ΔpH as a measure of total pH defense(bicarbonate and nonbicarbonate buffering, respiratory compensation) increased steadily from 61 ± 14 (SE) to 120 ± 9 mmol/l.Δ[HCO3-]plasma/ΔpH (bicarbonate buffering and respiratory compensation) rose in a parallel manner from 42 ± 10 to 96± 7 mmol/l. The difference between-Δ[lactate]plasma/ΔpH andΔ[HCO3-]plasma/ΔpH amounted to 17 ± 3 mmol/l. The nonbicarbonate buffer value can be used to estimate the effect of hyperventilation and to calculate buffer capacities for constant pCO2 and thus nonrespiratory (nr) pH changes.-Δ[lactate]plasma/ΔpHnr was initially higher than-Δ[lactate]plasma/ΔpH (71 + 8 mmol/l) because of temporarily increasing pCO2, reached a minimum of 57 ± 1 mmol/l after 6 min and than increased again up to the initial values.Δ[HCO3-]plasma/ΔpHnr followed an equal time course but at a lower level (difference 17 mmol/l). Calculation ofΔ[HCO3-]plasma/ΔpHnr from initial values by use of the Henderson-Hasselbalch equation yielded only slightly different values demonstrating that no considerable bicarbonate exchange occurred with the cells. The apparently increasing total pH defense after the Wingate test resulted from a consistently decreased pCO2. The relative importance of this respiratory compensation increases with decreasing lactic acid concentration and thus decreasing total pH changes.

Carbon dioxide transport in alligator blood and its erythrocyte permeability to anions and water.

Deoxygenation of alligator red blood cells (RBCs) caused binding of two HCO3- equivalents per hemoglobin (Hb) tetramer at physiological pH. At lowered pH, some HCO3- binding also occurred to oxygenated Hb. The erythrocytic total CO2 content was large, and Hb-bound HCO3-, free HCO3-, and carbamate contributed about equally in deoxygenated cells. The nonbicarbonate buffer values of RBCs and Hb were high, and the Hb showed a significant fixed acid Haldane effect. Binding of HCO3- on deoxygenation occurred without a change in RBC intracellular pH, revealing equivalence between oxylabile HCO3- and H+ binding. Erythrocyte volume, plasma pH, and plasma HCO3- concentration also varied little with the degree of oxygenation. Diffusional water permeability was higher in oxygenated than deoxygenated RBCs. The RBCs have rapid band 3-mediated Cl- and HCO3- transport, which was not affected by degree of oxygenation, but net fluxes of Cl- and HCO3- via the anion exchanger are small during blood circulation at rest. Most of the CO2 taken up into the blood as it flows through tissue capillaries is carried within the erythrocytes as Hb-bound HCO3- until CO2 is excreted when blood flows through pulmonary capillaries.

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.

Esophagoprotective potential of cisapride. An additional benefit for gastroesophageal reflux disease.

Cisapride is a novel prokinetic agent that releases acetylcholine at the level of the myenteric plexus. Acetylcholine also plays a role in the secretory function of salivary glands evoked by intraesophagal mechanical and chemical stimulation, mediated through the esophagosalivary reflex. The impact, however, of cisapride on salivary protective components mediated by esophagosalivary reflex remains unknown. Therefore, we have studied salivary pH, bicarbonate, nonbicarbonate, glycoconjugate, protein, EGF, TGF-alpha, and PGE2 before and after the administration of cisapride. The study was conducted in 20 asymptomatic volunteers (9 women and 11 men, mean age 36, range 26-52). Salivary secretions were collected under basal conditions and during masticatory, mechanical, and chemical stimulation before and after four days of cisapride administration (10 or 20 mg four times a day). Cisapride administration resulted in a 45% increase in salivary volume during the basal condition (P < 0.01), a 32% increase during mastication (P < 0.05), a 53% increase during mechanical (P < 0.05), and a 51% increase during chemical (P < 0.01) stimulation. Cisapride administration resulted also in a significant increase in salivary protein output (P < 0.05), salivary bicarbonate (P < 0.05), and nonbicarbonate buffers (P < 0.05), and salivary EGF (P < 0.05). Salivary glycoconjugate significantly increased only during mechanical stimulation with the catheter and at the end of the esophageal perfusion procedure (P < 0.05). Although a similar trend was also recorded during the analysis of salivary PGE2, this difference did not reach statistical significance. Salivary pH and TGF-alpha before and after cisapride administration remained unchanged. The stimulatory impact of cisapride on salivary volume and inorganic (bicarbonate and nonbicarbonate buffers) and organic (protein, glycoconjugate, and EGF) protective components would benefit patients with GERD and would also be potential therapy for xerostomia.

Temperature-dependent shift of pHi in fish white muscle: contributions of passive and active processes.

This study was designed to determine the mechanisms causing temperature-induced pH shifts in the white muscle of the marine teleost Zoarces viviparus. The white musculature undergoes an intracellular acidification with increasing body temperature at a slope of the pH-temperature relationship equal to -0.016 +/- 0.003 U/degree C. This is in good accordance with the overall relationship between the change in pK and the change in temperature of the intracellular proteins, which was determined to be -0.013 +/- 0.001 U/degree C. Thus the dissociation state of muscle proteins is kept fairly constant in white muscle of Zoarces viviparus. The passive component of the observed pH shift, which is due to the physicochemical response of the intracellular buffers to temperature change, accounts for only 35% of the pH transition. Ventilatory adjustment of intracellular PCO2 does not contribute to the temperature-induced shift of intracellular pH (pHi) in Zoarces viviparus. Therefore, the remaining 65% of pH adjustment must be ascribed to ion exchange mechanisms. The nonbicarbonate buffer value amounted to 34.4 +/- 2.3 meq.pH-1 kg cell water-1 at 12 degrees C and decreased slightly but not significantly with temperature. On the basis of our data we calculated that a removal of 0.52 mmol base equivalents.kg cell water-1.degree C-1 was necessary to shift pHi to its new steady state.

Respiratory, Acid-Base, and Metabolic Responses of the Christmas Island Blue Crab, Cardisoma hirtipes (Dana), during Simulated Environmental Conditions

The dependency of the Christmas Island blue crab, Cardisoma hirtipes, on fresh water for respiratory gas exchange and transport was investigated in laboratory simulations. The gas exchange rates of air-breathing C. hirtipes were similar to those of other land crabs but decreased to 20% in submerged crabs. Crabs with access to air maintained arterial and pulmonary O2 content (CO2) and partial pressure (PO2), while in submerged crabs the PO2 and CO2 rapidly decreased (by 50%). There was no anaerobiosis, but haemolymph glucose concentration and cardiac output decreased when crabs were submersed, which suggests a hypometabolic state. Submersion induced a metabolic rather than a respiratory alkalosis, and since respiratory gas exchange was low, CO2 excretion to water was unimportant. Cardisoma hirtipes haemocyanin (Hc) has high O2 affinity but low pH sensitivity, which facilitates O2 uptake from hypoxic environments. The high Hc-O2 affinity supports O2 loading but may prevent access to a venous O2 reserve. Calcium, magnesium, and urate, but not L-lactate, were effectors of Hc-O2 affinity. In submerged crabs increased circulating urate maintained haemolymph O2 content. The CO2 capacitance and nonbicarbonate buffering of the haemolymph were relatively low. A significant Haldane effect seemed important for CO2 excretion but would require CO2 and O2 exchange to occur at the same organ (gills or lungs). Submersion interferes with respiration and is not needed for haemolymph acid-base balance; thus; C. hirtipes is an air-breathing crab.

Air Breathing by the Purple Shore Crab,Hemigrapsus nudus(Dana). III. Haemocyanin Function in Respiratory Gas Transport

The functional properties of the haemolymph and haemocyanin (Hc) of Hemigrapsus nudus were investigated with respect to the amphibious behaviour of this crab. The O₂ affinity of the Hc was decreased at higher temperature (∆H = −30 to −40 kJ mol⁻¹). Haemocyanin-O₂ affinity was sensitive to pH (Bohr factor = −0.843 at 15° C) but essentially insensitive to L-lactate (Δ log P50}/Δ log [lactate] = −0.053). The pH sensitivity of Hemigrapsus Hc was dependent on temperature (Bohr factor = −0.44 at 5°C, −0.90 at 25° C). Increasing CO₂ had no specific effect, nor was Hc-O₂ affinity increased by increasing levels of dopamine. Urate markedly increased the O₂ affinity of Hemigrapsus Hc (Δ log P50/Δ log [urate] = −0.203), and together with H+, it would seem to be the major organic effector of Hc-O₂ affinity. Increasing haemolymph Ca both potentiated Hc-O₂ affinity and decreased the magnitude of the Bohr shift. The potentiating effect was more pronounced at lower than normal Ca concentration, while Mg had little effect. The CO₂ capacitance of the haemolymph was more dependent on temperature than could be accounted for by the reduction in CO₂ solubility at higher temperature (CO₂ capacitance = 0.44-0.91 mmol L⁻¹ mmHg⁻¹). Consistent with a relatively low haemolymph protein concentration, the nonbicarbonate buffer was low (Δ[]/ΔpH = − 4.80), and thus changes in H+ concentration would promote large changes in pH and Hc-O₂ affinity. A Haldane effect was detected at 25° C Relating these data to in vivo measurements showed that acid-base balance in Hemigrapsus emerging from 10° C water into 25° C air was likely managed separately from CO₂ excretion. In crabs breathing 10° C water, the Hc transported 50% of the used O₂, while in animals breathing 25° C air the amount of O₂ so transported rose to 85%. Emersion-induced acidosis initially promoted a large decrease in O₂ affinity, reduced oxygenation, and promoted a decrease in the arterial-venous O₂ content difference. However, a subsequent metabolic alkalosis and an elevation in haemolymph urate reestablished the transport role of the Hc. Thus the pH sensitivity, especially at high temperatures, and the effect of urate seem crucial to the amphibious behaviour of Hemigrapsus, whose modulator systems are quite unlike those found in land crabs. Further work is required to determine whether these features represent a transitional stage between water and air breathing or whether they are specific adaptations to the supratidal environment or indeed are peculiar to grapsid crabs.

BUFFERING AGAINST LACTIC ACID DURING EXERCISE 531

The acidosis caused by lactic acid during exercise is attenuated by bicarbonate and nonbicarbonate buffers and by reduction of PCO2 via hyperventilation. An estimate of the total effect in the extracellular space can be obtained from Δ[Lac]/ΔpHtot in arterial blood. If the respiratory (r) changes in PCO2, pH and [HCO3] are known, a nonrespiratory buffer value (Δ[Lac]/ΔpHnr) can be calculated. For this correction an in vivo CO2-equilibration curve of blood has to be measured. In 12 well-trained subjects (10 males, 2 females: 30.8±5.4 (SD) years, ˙VO2max 61.2 ± 8.2 ml/kg·min) we determined Δ[Lac]/Δ pHtot during a graded bicycle ergometer test. Lactic acid concentration and acid-base status were measured in arterialized ear lobe blood. During hypocapnia and hypercapnia the same quantities were determined in arterialized venous blood. The relation between Δ[HCO5]r and ΔpHr as well as between ΔLac and ΔpHtot in the exercise experiments was approximately linear. The mean of the individual regression coefficients for Δ[Lac]/Δptot amounted to - 71 ± 24 mmol/l. MeanΔ[HCO3]/ΔpHr was much lower (- 19.2±4.2 mmol/l) and scattered less. Δ[Lac]/ΔpHnr showed a decreased mean value with a reduced standard deviation (-54 ± 13 mmol/l) compared to the total effect. This quantity seems to be relatively stable and can be considered as a measure of buffers available to the extracellular space(mainly bicarbonates and proteins in red cells, plasma and interstitial fluid). In contrast the contribution of ventilation to acid-base stability during exercise is rather variable.

Brain tissue acid-base response to hypercapnia in neurosurgical patients

These studies were conducted in neurosurgical patients to determine brain tissue nonbicarbonate buffering of pH changes during hypercapnia. Following a craniotomy, a sensor which continuously measures oxygen pressure, carbon dioxide pressure, pH and temperature was inserted into cortex tissue of nine subjects. Bicarbonate concentration was calculated from the Henderson-Hasselbach equation. Following baseline measures, PaCO2 was increased 10mmHg for 10 min. Tissue pCO2 increased 9 mmHg (p < 0.05) without a change in tissue pO2. In six patients, tissue bicarbonate concentration increased from 18 to 20 meq L-1 (p < 0.05), indicating a 40-50% attenuation of the increase in hydrogen ion (H+) by nonbicarbonate buffering mechanisms. Three patients showed no increase in tissue bicarbonate during hypercapnia; 2 had baseline tissue pH less than 6.5 and one displayed signs of tissue hypoxia during the CO2 challenge. In all patients, increases in tissue H+ during hypercapnia were related to baseline tissue bicarbonate concentration. Marked increases in H+ were seen when baseline bicarbonate decreased below 10 meq L-1. These results suggest that when tissue bicarbonate is depleted, the risk of H+ induced injury during hypercapnia is increased.