Proton Load Research Articles

Removal of an inorganic acid load in subjects with ketoacidosis of chronic fasting

When a large inorganic acid load is ingested by normals, the proton load is eliminated because the rate of excretion of ammonium can rise to 200 to 300 mmol/day. In subjects with ketoacidosis of chronic fasting, such a large increase in the rate of excretion of ammonium might not be possible because of ATP balance considerations in proximal cells. Subjects with ketoacidosis of chronic fasting excreted less net acid as defined in the conventional way when they consumed a large inorganic acid load (136 +/- 6 vs. 176 +/- 26 mmol/day in control fasted subjects). Nevertheless, the vast majority of this inorganic acid load was eliminated because they were in steady state and had only a slightly lower concentration of bicarbonate (13 +/- 0.6 vs. 15 +/- 0.5 mmol/liter) and ketoacid anions (3.3 +/- 0.2 vs. 5.5 +/- 0.2 mmol/liter) in their blood. Using a definition of net acid excretion where the component of bicarbonate loss was expanded to include "potential bicarbonate" (ketoacid anions) in the urine, the rate of excretion of net acid was higher in subjects who ingested the inorganic acid load, owing to a much lower rate of excretion of ketoacid anions (9 +/- 2 vs. 120 +/- 7 mmol/day). This lower rate of excretion was not only due to a lower filtered load, but also to a higher fractional reabsorption of ketoacid anions during acidosis (97 +/- 0.1 vs. 77 +/- 0.2%). This higher fractional reabsorption could not be explained by a lower filtered load of ketoacid anions or to a restricted intake of sodium.(ABSTRACT TRUNCATED AT 250 WORDS)

Internal and External Proton Load to Forest Soils in Northern Germany

AbstractBoth external and internal proton sources contribute to total H+ load of the soil in terrestrial ecosystems. The most important internal net proton production (INP) processes are (a) accumulation of a surplus of inorganic cations over anions in organic matter, (b) net production and protolysis of organic acids, (c) dissociation of carbonic acid from root and decomposer respiration, (d) net nitrification of organic N, (e) uptake of a surplus of deposited NH+4 over deposited NO−3 or nitrification of deposited NH+4, (f) buffering of deposited H+ in the canopy and recharging of foliar buffer systems with subsequent H+‐release to the soil. Processes (a) through (d) are proton production processes due to ecosystem state and site conditions; (e) and (f) are due to atmospheric deposition and must be regarded as part of acid deposition. The sum of the rates of all processes plus free acidity (H+) flux in throughfall constitute total proton load (TPL) to a soil. Rates of INP and TPL were evaluated for six experimental forests in northwestern West Germany, which had been monitored in long‐term studies. Internal sources are relevant contributors to total proton load. At five of the six sites, however, H+ load due to atmospheric deposition exceeds 70% of TPL. Total acidity budgets show that soils in the aluminum‐buffer‐range become acid exchangers (3H+ → Al3+), i.e., they almost quantitatively transfer the incoming amount of acid (TPL) to deeper layers of the seepage conductor and eventually the hydrosphere. A comparison of the evaluated TPL rates with maximum rates of buffering by silicate weathering reported in the literature indicates that all carbonate‐free soils will further acidify and reach the Al buffer range.

Effect of nimodipine on the regional cerebral acidosis accompanying thiamine deficiency in the rat.

The effect of the calcium channel blocker nimodipine on the previously described regional cerebral acidosis accompanying thiamine deficiency was investigated. Local cerebral pH (LCpH) and blood flow (LCBF) were separately determined autoradiographically in normal and 16-day thiamine-deficient rats administered the calcium antagonist drug and compared to appropriate controls. Nimodipine did not modify LCpH in normal brain. In thiamine deficiency, nimodipine significantly raised LCpH in 5 of 17 structures evaluated, two of which, the medial dorsal nucleus of the thalamus and the mammillary body, are vulnerable to the development of histological lesions in this condition. Although the calcium blocker augmented LCBF in normal brain, it had no effect on the hyperperfusion already present by day 16 of thiamine deprivation. Thus, the pH changes we are reporting are probably not related to an effect on cerebral perfusion, but could have resulted from an improved ability of the brain to reduce its proton load in the presence of nimodipine. These results may have wider therapeutic implications than in thiamine deficiency alone.

Determination of buffering capacity of rat myocardium during ischemia

To determine the buffering capacity of ischemic rat myocardium, lactate production was altered by glycogen depletion prior to total global ischemia. Lactate production was monitored by 1H-NMR spectroscopy in perfused rat hearts and determined by enzymatic assay of freeze-clamped tissue extracts. Intracellular pH was measured by 31P-NMR spectroscopy. The relationship between total lactate produced and pH varied considerably, depending on the final pH reached. At pH>6.4 this relationship is linear with a total buffering capacity (Δlactate/ΔpH) of 25 μmol H+/g wet weight per pH unit. At lower pH values (pH<6.4), the total buffering capacity increases progressively. Since ischemia is invariably accompanied by ATP and phosphocreatine (PCr) hydrolysis, the proton production/consumption during high-energy phosphate hydrolysis must be considered when evaluating the intrinsic buffering capacity of the myocardium against proton loads produced by lactate production from glucose and glycogen. Schemes are presented which allow an estimation of the contribution of ATP and PCr hydrolysis and the buffering by the CO2/HCO3− system during ischemia. At pH>6.4, the majority (about 60%) of buffering is due to hydrolysis of adenosine triphosphate, phosphocreatine in the heart, and neutralization of sodium bicarbonate in the perfusate. At pH<6.4 an increasing proportion of cardiac buffering is from intrinsic cardiac buffers, most likely from intracellular proteins. After correction for these contributions to the observed total cardiac buffering capacity, the intrinsic buffering capacity of the myocardium can be accounted for by a high capacity (170 μmol/g wet weight) but low pKa (5.2) buffering system.

Determination of buffering capacity of rat myocardium during ischemia

To determine the buffering capacity of ischemic rat myocardium, lactate production was altered by glycogen depletion prior to total global ischemia. Lactate production was monitored by 1H-NMR spectroscopy in perfused rat hearts and determined by enzymatic assay of freeze-clamped tissue extracts. Intracellular pH was measured by 31P-NMR spectroscopy. The relationship between total lactate produced and pH varied considerably, depending on the final pH reached. At pH> 6.4 this relationship is linear with a total buffering capacity (Δlactate/ΔpH) of 25 μmol H +/g wet weight per pH unit. At lower pH values (pH< 6.4), the total buffering capacity increases progressively. Since ischemia is invariably accompanied by ATP and phosphocreatine (PCr) hydrolysis, the proton production/consumption during high-energy phosphate hydrolysis must be considered when evaluating the intrinsic buffering capacity of the myocardum against proton loads produced by lactate production from glucose and glycogen. Schemes are presented which allow an estimation of the contribution of ATP and PCr hydrolysis and the buffering by the CO 2/HCO 3 − system during ischemia. At pH> 6.4, the majority (about 60%) of buffering is due to hydrolysis of adenosine triphosphate, phosphocreatine in the heart, and neutralization of sodium bicarbonate in the perfusate. At pH< 6.4 an increasing proportion of cardiac buffering is from intrinsic cardiac buffers, most likely from intracellular proteins. After correction for these contributions to the observed total cardiac buffering capacity, the intrinsic buffering capacity of the myocardium can be accounted for by a high capacity (170 μmol/g wet weight) but low p K a (5.2) buffering system.

Physiological Responses of the Rock Crab Cancer irroratus (Say) to Environmental Hyperoxia. I. Acid-Base Regulation

Hemolymph acid-base and ion levels and acidic equivalent exchange with the experimental water were monitored in rock crabs (Cancer irroratus Say) exposed to control normoxia (PIo2 ≃ 150 torr), 48 h of hyperoxia (Po2 ≃ 512 torr), and 24 h of subsequent normoxic recovery. Hemolymph CO₂ binding was assessed in vitro on oxygenated and deoxygenated samples. Settled normoxic crabs had the following acid-base status: pH—8.01; Pco2—2.1 torr, and [HCO₃⁻]-9.3 meq·liter⁻¹ and appeared to be in proton balance with the experimental water. Within 6 h of exposure to hyperoxia, the hemolymph exhibited a significant acidosis (0.15 pH units) that was due to respiratory CO2 (Pco2 increased by 50%). This acid-base imbalance was restored between 6 and 24 h by a 50% increase in [HCO₃⁻]. This coincided with a 13-fold increase in excretion of acidic equivalents (primarily titratable) into the experimental water that continued for up to 10 h. Numerically, there was excellent correspondence between acid efflux and the magnitude of the extracellular proton load. Although crabs continued to hypoventilate, preexperimental Pco2 was reestablished by 24 h, suggesting that the original hypercapnia had been due to a perfusion limitation. Between 24 and 48 h, circulating [HCO₃⁻] was also restored to resting levels accompanied by an equivalent net base excretion into the bathing medium. When normoxia was reinstated, hemolymph exhibited a reduction in Pco2 plus a further reduction in [HCO₃⁻] at constant Pco2, making pH alkalotic. The base efflux that persisted into the recovery period significantly exceeded that required to restore extracellular acid-base balance. It is suggested that this base load originated intracellularly and that the reduced cardiac output during hyperoxia limited its removal into the hemolymph. Circulating lactate exhibited a similar washout effect during recovery. Hemolymph of C. irroratus had a low nonbicarbonate buffer value (β) corresponding to reduced protein concentration. However, the Haldane effect, which theoretically could account for the release of 2.13 mmol CO2 per mmol O2 bound, was larger than observed in other decapods.

Haemolymph Acid-Base, Electrolyte and Gas Status During Sustained Voluntary Activity in the Land Hermit Crab (Coenobita Compressus)

ABSTRACT After 3 h (50 m) of voluntary walking, the haemolymph pH of the land hermit crab Coenobita compressus (H. Milne Edwards) decreased by 0·4units. This was accompanied by increases in CO2 tension bicarbonate (HCO3- + CO32-) and lactate concentrations. The hypercapnic acidosis was partially compensated by metabolic bicarbonate accumulation and an H+ deficit developed. Unloaded crabs accumulated less of a proton load than crabs transporting mollusc shells. During activity, oxygenation of the haemocyanin (HCy) accounted for the release of 0·3 mmol CO21-1, via the Haldane effect, which was seven times more than in settled crabs. Control acid-base balance was re-established within 1 h of recovery. At this time, acidic equivalents were excreted at a mean flux rate of 5 mequivkg-1 h-1 into a source of external water. [Na+] and the ratio of [Na+] : [Cl-] increased during exercise. Coenobita haemolymph had a high O2-carrying capacity . HCy oxygen-binding characteristics were typical of other decapods (ϕ = -0·44), yet no lactate sensitivity was apparent. Settled in vivo values of O2 tension and content were located around the half-saturation tension (P50) of the dissociation curve. During exercise, increased and an unopposed Bohr shift decreased the O2-binding affinity, thereby reducing postbranchial saturation. Quantitatively, however, compensations in cardiac output were more instrumental in increasing the O2 delivery to respiring tissues. During recovery, haemolymph remained high and the venous reserve doubled.

Tissue intracellular acid-base status and the fate of lactate after exhaustive exercise in the rainbow trout.

Exhaustive 'burst-type' exercise in the rainbow trout resulted in a severe acidosis in the white muscle, with pHi dropping from 7.21 to a low of 6.62, as measured by DMO distribution. An accumulation of lactate and pyruvate, depletions of glycogen, ATP and CP stores, and a fluid shift from the extracellular fluid to the intracellular fluid of white muscle were associated with the acidosis. The proton load was in excess of the lactate load by an amount equivalent to the drop in ATP, suggesting that there was an uncoupling of ATP hydrolysis and glycolysis. Initially, lactate was cleared more quickly than protons from the muscle, a difference that was reflected in the blood. It is suggested that during the early period of recovery (0-4 h), the bulk of the lactate was oxidized in situ, restoring pHi to a point compatible with glyconeogenesis. At that time, lactate and H+ were used as substrates for in situ glyconeogenesis, which was complete by 24 h. During this time, lactate and H+ disappearance could account for about 75% of the glycogen resynthesized. The liver and heart showed an accumulation of lactate, and it is postulated that this occurred as a result of uptake from the blood. Associated with the lactate load in these tissues was a metabolic alkalosis. Except for an apparent acidosis immediately after exercise, the acid-base status of the brain was not appreciably affected. Despite the extracellular acidosis, red cell pHi remained nearly constant.

Anthropogenic and natural acidification in terrestrial ecosystems

The total proton load found in these ecosystems exceeds by far the known rates of buffering in soils by silicate weathering and release of basic cations (see above). Under the present proton load most forest soils will therefore acidify and besides losses of nutrients the occurrence of possible toxic ions in the soil unavoidable (Al-buffer range)20, 21. The proportion of the total proton load of the soil that is represented by the internal production emphasizes the importance of acid deposition as main cause of soil acidification and destabilization of forest ecosystems under Central European conditions.

Responses of A Stenohaline Freshwater Teleost (Catostomus Commersoni) to Hypersaline Exposure: I. The Dependence of Plasma Ph and Bicarbonate Concentration on Electrolyte Regulation

ABSTRACT The effects of exposure to 0·94% (300mosmoll−1) sodium chloride on plasma electrolyte and acid-base status were examined in the freshwater stenohaline teleost Catostomus commersoni (Lacépède), the white sucker. Four days’ exposure to this maximum sublethal salinity resulted in an increase in plasma concentrations of both sodium and chloride but a decrease in the Na+/Cl− ratio. Since the plasma concentrations of free amino acids and other strong ions - Ca2+, Mg2+ and K+ - remained unchanged, plasma strong ion difference (SID) decreased. Additionally, plasma pH and bicarbonate concentration decreased at constant. The changes in electrolyte and acid-base status that occurred after the 96 h were not appreciably altered after a further 2–3 weeks of saline exposure. The ambient calcium concentration had no influence on these results. Haemolymph non-bicarbonate buffer capacity (β) calculated as Δ[HCO3−]/ ΔpH, increased in saline-exposed fish. Consequently ΔH+, the apparent proton load, was zero despite the apparent change in acid-base status. Although β was directly proportional to the haemoglobin concentration in both control and experimental fish, this could not account for the increase in β since haemoglobin remained at control values. These results can be explained solely by the change in plasma SID and serve to illustrate the dependence of plasma acid-base status on the prevailing electrolyte characteristics, weak acid concentration and .

The effect of acid–base balance on fatigue of skeletal muscle

H+ ions are generated rapidly when muscles are maximally activated. This results in an intracellular proton load. Typical proton loads in active muscles reach a level of 20-25 mumol X g-1, resulting in a fall in intracellular pH of 0.3-0.5 units in mammalian muscle and 0.6-0.8 units in frog muscle. In isolated frog muscles stimulated to fatigue a proton load of this magnitude is developed, and at the same time maximum isometric force is suppressed by 70-80%. Proton loss is slowed when external pH is kept low. This is paralleled by a slow recovery of contractile tension and seems to support the idea that suppression results from intracellular acidosis. Nonfatigued muscles subjected to similar intracellular proton loads by high CO2 levels show a suppression of maximal tension by only about 30%. This indicates that only a part of the suppression during fatigue is normally due to the direct effect of intracellular acidosis. Further evidence for a component of fatigue that is not due to intracellular acidosis is provided by the fact that some muscle preparations (rat diaphragm) can be fatigued with very little lactate accumulation and very low proton loads. Even under these conditions, a low external pH (6.2) can slow recovery of tension development 10-fold compared with normal pH (7.4). We must conclude that there are at least two components to fatigue. One, due to a direct effect of intracellular acidosis, acting directly on the myofibrils, accounts for a part of the suppression of contractile force. A second, which in many cases may be the major component, is not dependent on intracellular acidosis. This component seems to be due to a change of state in one or more of the steps of the excitation-contraction coupling process. Reversal of this state is sensitive to external pH which suggests that this component is accessible from the outside of the cell.

Physiological Consequences of Severe Exercise in the Inactive Benthic Flathead Sole (Hippoglossoides Elassodon): a Comparison With the Active Pelagic Rainbow Trout (Salmo Gairdneri)

ABSTRACT Chronically cannulated flathead sole were subjected to 10 min of either moderate or exhausting burst exercise and monitored over a 12 h recovery period. Acid-base disturbances were more severe after exhausting exercise, but ionic and haematological changes were the same in the two treatments. Most effects were qualitatively similar to those previously described in severely exercised rainbow trout (Turner, Wood &amp; Clark, 1983). Specific differences are discussed and related to the different external environments (sea water vs fresh water), exercise capabilities and ecologies of the two species. The most striking divergence occurred in lactate (La−) and metabolic proton dynamics. Post-exercise La− levels in white muscle in sole were less than half those in trout but declined much more slowly. In contrast to the situation in trout, muscle [La−] remained significantly elevated and a large muscle to blood La− gradient persisted even after 12 h recovery. Blood [La−] underwent only minimal elevation (&amp;lt; 2 mequiv l−1), and blood metabolic proton load greatly exceeded ΔLa− throughout the recovery period, effects directly opposite those in trout. This observed excess of over ΔLa− in the blood of exercised sole is probably not due to a preferential removal mechanism, because and ΔLa− disappeared from the blood at similar rates after an intra-arterial infusion of lactic acid in resting animals. It is therefore argued that the phenomenon reflects a differential release of the two metabolites from the white muscle of the sole, La− being strictly retained in the muscle for gluconeogenesis in situ.

Intracellular pH.

Intracellular pH.

The response of the kidney of the freshwater rainbow trout to true metabolic acidosis.

Infusion of lactic acid into the bloodstream of trout produced a short-lived depression of blood pH and a long-lasting elevation of blood lactate. The lactate injected was distributed in a volume of 198 ml/kg. Renal excretion of lactate anion and total acid increased by approximately equal amounts during the period of high blood lactate levels, but total renal loss over 72 h accounted for only 2% of the lactate load and 6% of the proton load. Comparable differences in the time courses of blood lactate and pH changes occurred when lactacidosis was induced endogenously by normocapnic hypoxia. The immediate response of the kidney was similar to that with lactic acid infusion, but there was a long-lasting (12-72 + h) elevation of urinary acid efflux that was not associated with lactate excretion. Following hypoxia, renal excretion over 72 h accounted for 1% of the estimated lactate load and 12-25% of the proton load. A renal lactate threshold of 4-10 muequiv/ml prevents significant urinary lactate excretion. The response of the trout kidney to true metabolic acidosis is similar to that of the mammalian kidney.