Chloride Depletion Research Articles

Na+-H+ antiporter in posthypercapnic state.

Posthypercapnic metabolic alkalosis has been attributed to decreased HCO3 excretion because of low glomerular filtration rate (GFR), volume contraction, or chloride depletion. We have previously shown that chronic hypercapnia enhances the Vmax of the Na+-H+ antiporter. We reasoned that an increased Vmax of the Na+-H+ antiporter could play a role in the maintenance of posthypercapnic metabolic alkalosis. To test this hypothesis, we measured the kinetics of the Na+-H+ antiporter by the dissipation of the quenching of acridine orange fluorescence in purified brush-border membrane obtained from posthypercapnic rabbits. The kinetic parameters were measured in controls and in rabbits that were exposed to hypercapnia for 48 h and then allowed to breathe room air for 3, 24, or 48 h. In luminal membranes prepared from posthypercapnic animals, the Vmax of the Na+-H+ antiporter was significantly increased after 3 and 24 h but not after 48 h compared with controls. The increase in Vmax was not different from that of hypercapnic animals. There was no difference in the Km of the Na+-H+ antiporter among these five groups. Amiloride inhibited the Vmax equally in membranes from control and posthypercapnic rabbits. Proton permeability was comparable among the groups. These data indicate that the increase in Vmax in posthypercapnic rabbits is mediated through the electroneutral Na+-H+ exchange and not through conductive H+ and Na+ pathway. Glucose uptake was not different in control and posthypercapnia, indicating a selective increase in Na+-H+ antiporter activity. At 3 and 24 h posthypercapnia, HCO3 concentration was higher than control.(ABSTRACT TRUNCATED AT 250 WORDS)

Importance of chloride for the correction of chronic metabolic alkalosis in the rat.

To determine whether chloride repletion without sodium could correct chronic chloride depletion metabolic alkalosis (CDA) in Sprague-Dawley rats without volume expansion and without increasing glomerular filtration rate (GFR), CDA was generated by peritoneal dialysis (PD) against 0.15 M NaHCO3 and maintained for 7-10 days by a chloride-restricted diet supplemented with sodium and potassium salts. Control animals were dialyzed against Ringer bicarbonate. The maintenance period of chronic CDA, compared with control, was characterized by hypokalemic metabolic alkalosis (serum TCO2 31.9 +/- 0.6 vs. 23.1 +/- 0.5 meq/l, P less than 0.05), volume contraction (plasma volume 3.76 +/- 0.08 vs. 4.19 +/- 0.22 ml/100 g body wt, P less than 0.05), decreased GFR (838 +/- 84 vs. 1045 +/- 45 microliters.min-1.100 g body wt-1, P less than 0.05), increased plasma renin activity (PRA) (63 +/- 13 vs. 12 +/- 3 ng.ml-1.h-1, P less than 0.05), but unchanged plasma aldosterone concentrations (PAC) (4.1 +/- 1.0 vs. 3.4 +/- 1.6 ng/dl, P = NS). Complete correction of chronic CDA was accomplished by 24 h of ingestion of choline chloride drink, and despite negative sodium balance, neutral potassium balance, continued bicarbonate ingestion, and persistent volume contraction (plasma volume 3.76 +/- 0.08 vs. 3.73 +/- 0.12 ml/100 g body wt pre- and postcorrection, P = NS), GFR remained decreased (659 +/- 87 vs. 1,045 +/- 45 microliters.min-1.100 g body wt-1, P less than 0.05), PRA decreased (63 +/- 13 vs. 33 +/- 5 ng.ml-1.h-1, P less than 0.05), but PAC did not change (4.1 +/- 1.0 vs. 6.1 +/- 1.6 ng/dl, P = NS) after correction of CDA.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfate inhibition of photosystem II oxygen evolving complex

Effect of sulfate on the oxygen evolution in barley Photosystem II membrane fraction was investigated. Purified Photosystem II membrane fraction was exposed to sulfate effect in dark or under dim light illumination. The presence of 10 mM CaCl2 during the sulfate treatments prevented the loss of oxygen evolution. The protection was complete even at the concentration of 50 mM Na2SO4. However, light stimulated sulfate inhibition of oxygen evolution by the Photosystem II. After incubation with sulfate, we found there was depletion of 18 and 23 kDa polypeptides in Photosystem II complex. Here we provide new evidence that sulfate inhibition of oxygen evolution can be caused by depletion of chloride and calcium ions from the water splitting complex rather than by partial depletion of 18 and 23 kDa polypeptides from the complex.

Respiratory burst facilitates the digestion of Escherichia coli killed by polymorphonuclear leukocytes.

We examined factors that may limit degradation of bacterial protein of Escherichia coli S15 killed by polymorphonuclear leukocytes (PMN). Both human and rabbit PMN degraded up to 40% of [14C]amino acid-labeled protein of ingested and killed E. coli in 2 h as determined by loss of acid-precipitable radioactivity. In contrast, equally bactericidal broken-PMN preparations or isolated granules degraded only about 10% of bacterial protein regardless of pH. To determine whether activation of the respiratory burst contributes to digestion, we compared degradation by intact PMN in room air and under N2. Depletion of O2 by N2 flushing had no effect on the bactericidal activity of either human or rabbit PMN but reduced degradation by approximately 50%. Protein degradation during phagocytosis was also reduced in the presence of cyanide or azide, inhibitors of myeloperoxidase (MPO). PMN of two patients with chronic granulomatous disease ingested and killed E. coli S15 as well as did normal PMN but degraded bacterial protein as did normal PMN incubated under N2. The low degradative activity of PMN disrupted by sonication could be raised to nearly the level of intact PMN incubated in room air by preincubation of the PMN with 10(-7) M formyl-methionyl-leucyl-phenylalanine (fMLP) before sonication and by pretreatment of E. coli with MPO. Depletion of O2 or chloride during these preincubations with formyl-methionyl-leucyl-phenylalanine respectively, virtually abolished and markedly diminished stimulation of bacterial protein degradation. We conclude that enhanced MPO-mediated O2 metabolism of intact PMN plays a role in the digestion of killed E. coli.

THERMOLUMINESCENCE EVIDENCE FOR CHLORIDE REQUIREMENT IN THE S2→S3 TRANSITION OF THE WATER‐SPLITTING SYSTEM

Abstract— The role of chloride in photosynthetic oxygen evolution was investigated by means of thermoluminescence measurements. It was found that chloride depletion in isolated chloroplasts almost completely abolished the B1 thermoluminescence band (S3QB− recombination) but diminished only slightly the amplitude of the B2 band (S2QB− recombination). The B2 band could be excited to full intensity by the first flash of a flash series and subsequent flashes caused no further change in the amplitude of the band. These observations suggest a block in the S2→S3 transition of the water‐splitting system in chloride‐depleted chloroplasts. Readdition of chloride provided evidence that the inhibitory effect of chloride removal is reversible.

Mortality of smolt of Atlantic salmon, Salmo salar L., at low levels of aluminium in acidic softwater.

The level of aluminium toxic to freshwater fish depends on chemical factors, such as pH, calcium concentration, concentrations of ligands and chelators, and degree of chemical stability; on biological factors, such as species, lifestage and physiological status, as well as on temperature. Presmolt of Atlantic salmon (Salmo salar L.) are more sensitive to acidic waters than yearlings and eggs, and also more sensitive than other species of salmonids. Sublethal physiological stress (measured as a depletion of plasma chloride) has been observed in smolts of Atlantic salmon reared in the chronically acid (pH = 4.9-5.4) Lake Liervatn, SW Norway, at labile Al concentrations of 25-50 ..mu..g Al/L. To establish toxic levels of labile Al in this water, the authors exposed sublethally stressed salmon smolts from Lake Liervatn to lake water (pH = 5.07, Ca = 1.3 mg/L, labile Al = 38 ..mu..g Al/L) enriched with inorganic aluminium to three concentration levels of labile Al: 75, 137 and 177 ..mu..g Al/L.

Questioning Role of Hypochloremia in Bronchopulmonary Dysplasia

To the Editor.— In response to the article "Is Chloride Depletion an Important Contributing Cause of Death in Infants With Bronchopulmonary Dysplasia?" (Pediatrics l986;77:212-216), we are compelled to point out that furosemide (Lasix) therapy may well be directly responsible for the metabolic alterations observed. Hazinski (J Pediatr l985;l06:8l-85) beautifully demonstrated in rabbits that chronic furosemiode administration not only caused metabolic alkalosis (pH 7.46) associated with hypochloremia (Cl 84 mEq/L) but also resulted in compensatory alveolar hypoventilation and secondary respiratory acidosis (Paco2 55 mmHg).

Questioning Role of Hypochloremia in Bronchopulmonary Dysplasia

To the Editor.— The title of the recent report by Perlman et al asks an important question for those of us who frequently treat infants who have bronchopulmonary dysplasia ("Is Chloride Depletion an Important Contributing Cause of Death in Infants With Bronchopulmonary Dysplasia?" Pediatrics l986;77:2l2-2l6). They suggest that chloride deficiency may be an important factor in the poor outcome of patients with bronchopulmonary dysplasia. While I am sure no one will seriously suggest that severe hypochloremia will not have a deleterious effect on an already seriously ill infant, I do have questions regarding how they arrived at their conclusion.

Chloride depletions and enrichments in seafloor hydrothermal fluids: Constraints from experimental basalt alteration studies

Na-K-Ca-Cl fluid was reacted with diabase at 400° and 425°C, 400 bars and fluidrock mass ratio of 0.5 to assess the relative mobility of dissolved Cl. Fluids from the present experiments reveal relatively large time and temperature dependent decreases in Cl; temperature increase enhances Cl removal, whereas reaction progress has the opposite effect. These changes are not due to boiling and/or phase separation. At 400° and 425°C, 400 bars, Cl removal from solution is accompanied by Ca and Na fixation, respectively. Both experiments produced mixed-layer chlorite/smectite, clinozoisite and albite(?). Olivine was not detected by X-ray diffraction or petrographic analysis of run products from either experiment, however, we propose that the time dependent changes in dissolved Cl result from olivine replacement by an Fe-hydroxy chloride phase followed by hydration effects. Quenched and washed alteration products, however, did not reveal anomalous Cl, which suggests that the Cl-bearing phase is characterized by retrograde solubility. This is consistent with the relative magnitude of Cl fixation observed for experiments at both temperatures and from results of an isobaric cooling experiment. The experiments provide evidence for the non-conservative behavior of Cl during hydrothermal alteration of basalt. The data are particularly important in light of the Cl-depleted nature of some ridge crest hot spring fluids, and suggest temperatures of formation for these fluids of approximately 410°C, assuming sub-seafloor pressure of 400 bars. In addition, the retrograde solubility of the Cl-bearing phase responsible for Cl fixation during high temperature basalt alteration, may help to explain Cl enrichment in hot spring fluids which have conductively cooled below 350°C

Cerebral dysfunction following infantile dietary chloride deficiency

Twenty-two children who were chloride-depleted in infancy due to a chloride-deficient diet and who had resultant hypochloremic alkalosis were analyzed in regard to their signs and symptoms, metabolic studies, and growth parameters. Deceleration of weight, linear growth, and head growth occurred in most, and persistent growth failure occurred in some. The majority had cognitive deficits at follow-up. Comparison with growth parameters in a chronically malnourished group of children who had a variety of disorders revealed a similar degree of deceleration of weight (p = 0.50) and height (p = 0.70), but more severe deceleration of head growth (p = 0.01). Comparison with follow-up cognitive deficits reported in the United States medical literature in children with similar severity of nutritional deprivation indicates that the chloride-depleted infants had more frequent and more severe cognitive deficits (p = 0.09). Cognitive deficits have been documented in U.S. children who are nutritionally deprived only when disorders causing concomitant chloride depletion are responsible for the malnutrition.

The roles of the extrinsic subunits in Photosystem II as revealed by EPR

The effects of selective removal of extrinsic proteins on donor side electron transport in oxygen-evolving PS II particles were examined by monitoring the decay time of the EPR signal from the oxidized secondary donor, Z +, and the amplitude of the multiline manganese EPR signal. Removal of the 16 and 24 kDa proteins by washing with 1 M NaCl inhibits oxygen evolution, but rapid electron transfer to Z + still occurs as evidenced by the near absence of Signal II f. The absence of a multiline EPR signal shows that NaCl washing induces a modification of the oxygen-evolving complex which prevents the formation of the S 2 state. This modification is different from the one induced by chloride depletion of PS II particles, since in these a large multiline EPR signal is found. After removal of the 33 kDa protein with 1 M MgCl 2, Signal II f is generated after a light flash. Readdition of the 33 kDa component to the depleted membranes accelerates the reduction of Z +. Added calcium ions show a similar effect. These findings suggest that partial advancement through the oxygen-evolving cycle can occur in the absence of the 16 and 24 kDa proteins. The 33 kDa protein, on the other hand, may be necessary for such reactions to take place.

Heat inactivation of oxygen evolution in Photosystem II particles and its acceleration by chloride depletion and exogenous manganese

Heat inactivation of oxygen evolution by isolated Photosystem II particles was accelerated by Cl − depletion and exogenous Mn 2+. Weak red light also accelerated heat inactivation. Heat treatment released the 33, 24 and 18 kDa proteins and Mn from the Photosystem II particles. The protein release was stimulated by Cl − depletion and exogenous Mn 2+, and the Mn release was also stimulated by Cl − depletion. A 50% loss of Mn corresponded to full inactivation of oxygen evolution, whereas no direct correlation seemed to exist between the loss of any one protein and inactivation of oxygen evolution. Removal of the 24 and 18 kDa proteins from photosystem II particles only slightly decreased the heat stability of oxygen evolution.

Attenuation of cisplatinum-induced nephrotoxicity in the rat by high salt diet, furosemide and acetazolamide.

The influence of variations in sodium chloride diet, furosemide and acetazolamide on nephrotoxicity induced by cisplatinum have been investigated in the rat by measuring serum creatinine concentrations 5 days after cisplatinum (5 mg/kg, ip) administration. Sodium chloride depletion enhanced, while sodium chloride loading minimized changes in renal function. Increases in urine flow rate following a dextrose water load failed to alter the nephrotoxic response. Both furosemide and acetazolamide, given 30 min before cisplatinum, attenuated the nephrotoxic response. In contrast, neither sodium chloride loading, furosemide, nor acetazolamide influenced the change in renal function when given 30 min after cisplatinum. These observations indicate that renal damage due to cisplatinum can be modified by alterations in dietary salt and by diuretics and that the extent of ultimate renal damage is dependent on factors occurring immediately after cisplatinum administration.

A Multistage Model for the Development of Hydrochemical Zonation in Chalk Ground Waters

ABSTRACTGround waters from the Cretaceous Chalk of east‐central England display hydrochemical zonation comprising four water types. These are, in the general direction of ground‐water flow; Type I – calcium bicarbonate (CaHCO3) waters undersaturated with respect to calcite, Type II – CaHCO3 waters saturated with respect to calcite, Type III – waters showing sulfate (SO4) reduction and softening by ion exchange, and Type IV – saline waters. At first appearance these water types may be interpreted as related members in the classically recognized, long‐term sequence of natural chemical evolution of subsurface waters. This simple model, however, cannot be reconciled fully with all aspects of the hydrochemistry. For example, there is no satisfactory process that could explain an apparent depletion of chloride when moving from Type I to Type II waters, and transitional boundaries are absent between water Types II and III, and Types III and IV. Furthermore, the model lacks credibility in an area where recent geological events have radically disturbed the regional ground‐water flow regime. An alternative hydrochemical zonation model is proposed in which each water type evolves independently of adjacent water types as a function of its own unique aquifer flow history. This multistage model is supported by tritium and radiocarbon evidence and can be related to probable changes in the regional flow regime during the past 125,000 years.

Effects of chloride depletion on electron donation from the water-oxidizing complex to the photosystem II reaction center as measured by the microsecond rise of chlorophyll fluorescence in isolated pea chloroplasts

The role of Cl − in the electron transfer reactions of the oxidizing side of Photosystem II (PS II) has been studied by measuring the fluorescence yield changes corresponding to the reduction of P +-680, the PS II reaction center chlorophyll, by the secondary PS II donor, Z. In Cl −-depleted chloroplasts, a rapid rise in fluorescence yield was observed following the first and second flashes, but not during the third or subsequent flashes. These results indicate that there exists an additional endogenous electron donor beyond P-680 and Z in Cl −-depleted systems. In contrast, the terminal endogenous donor on the oxidizing side of PS II in Tris-washed preparations has previously been shown to be Z, the component giving rise to EPR signals II f and II vf. The rate of reduction of P +-680 in the Cl −-depleted chloroplasts was as rapid as that measured in uninhibited systems, within the time resolution of our instrument. Again, this is in contrast to Tris-washed preparations in which a dramatic decrease in the rate if this reaction has been previously reported. We have also carried out a preliminary study on the rate of rereduction of Z + in the Cl −-depleted system. Under steady-state conditions, the reduction half-time of Z + in uninhibited systems was about 450 μs, while in the Cl −-depleted chloroplasts, the reduction of Z + was biphasic, one phase with a half-time of about 120 ms, and a slower phase with a half-time of several seconds. The appearance of the quenching state due to P +-680 observed following the third flash on excitation of Cl −-depleted chloroplasts was delayed by two flashed when low concentrations of NH 2OH (20–50 μM) were included in the medium. Hydrazine at somewhat higher concentrations showed the same effect. This is taken to indicate that the reactions leading to PS II oxidation of NH 2OH or NH 2NH 2 are uninhibited by Cl − depletion. Addition of NH 2OH at low concentrations to Tris-washed chloroplasts did not alter the pattern of the fluorescence yield, indicating that the reactions leading to the NH 2OH oxidation present in Cl −-depleted systems are absent following Tris inhibition. The results are discussed in terms of an inhibition by Cl − depletion of the reactions of the oxygen-evolving complex. It is suggested that no intermediary redox couple exists between the oxygen-evolving complex and Z, and that Z + is reduced directly by Mn of the complex. In terms of the S-state model, Cl − depletion appears to inhibit the advancement of the mechanism beyond S 2, but not to inhibit the transitions from S 0 to S 1, or from S 1 to S 2.

Effects of acetylcholine and caerulein on 86Rb + efflux in the mouse pancreas. Evidence for a sodium-potassium-chloride cotransport system

The effect of acetylcholine and the cholecystokinin-like peptide, caerulein on the fractional efflux of 86Rb + from preloaded isolated segments of mouse pancreas were studied. Both secretagogues evoked a marked transient increase in 86Rb + efflux. The removal of Ca 2+ from the superfusing medium and addition of 10 −4 M EGTA, markedly reduced, but did not abolish the responses to either acetylcholine or caerulein. Furosemide ( 10 −5−10 −3 M ) or piretanide (10 −4 M) reduced the basal efflux and inhibited the secretagogue-elicited responses. Stimulus-induced 86Rb + outflow was abolished when the Cl − component of the superfusing solution was replaced by either NO 3 −, SO 4 2− or I − but not in case of replacement by Br −, When Na + was replaced with either Li + or choline + both acetylcholine and caerulein failed to elicit any detectable increase in 86Rb + outflow. However, when Tris + was substituted for Na +, acetylcholine caused a moderate increase in 86Rb + efflux which was abolished by either furosemide (10 −4 M) or chloride depletion (nitrate substitution). The removal of extracellular K + or pretreatment with 10 −3 M ouabain had little effect on secretagogue-evoked 86Rb + efflux. These results indicate the presence of a diuretic-sensitive Na +-K +-Cl − cotransport system in the mouse pancreatic acinar cell membrane.

Slow potential changes in mammalian muscle fibers during prolonged hyperpolarization: transport number effects and chloride depletion.

Mammalian skeletal muscle fibers exhibit large slow changes in membrane potential when hyperpolarized in standard chloride solutions. These large slow potential changes are radically reduced in low chloride solutions, where the faster and smaller potential change ("creep"), usually observed in amphibian fibers, becomes apparent. The slow potential change during a hyperpolarizing current pulse leads to an increase in apparent resistance of up to nine times the instantaneous value and takes minutes to reach a steady value. It then takes a similar time to decay very slowly back to the resting membrane potential after the current pulse. The halftime for the slow potential change was found to be inversely proportional to the current magnitude. From measurements of immediate post-pulse membrane potentials, assuming constant ionic permeabilities, the internal chloride concentration was calculated to decrease exponentially towards a steady value (e.g., for one fiber from 12.3 to 6.6 mM after a 330-sec pulse). The time course and magnitude of the concentration change were predicted from chloride transport number differences, and the known and measured properties of the fibers, and were found to agree very well with the values obtained from experimental measurements. In addition, the shapes of the V2-V1 responses, measured in the three-electrode current clamp set-up with either potassium chloride or potassium citrate current electrodes, were as predicted by transport number chloride depletion effects and were at variance with the predictions of a permeability change mechanism.

Reduction of renal blood flow and proximal bicarbonate reabsorption in rats by gentamicin

AbstractReduction of renal blood flow and proximal bicarbonate reabsorption in rats by gentamicin. Although aminoglycoside-induced acute renal failure occurs commonly, little is known about the mechanisms which alter renal hemodynamics. In sodium-depleted Sprague-Dawley rats treated with gentamicin, we measured RBF and GFR at the onset of this model of nephrotoxic acute renal failure. After 10 days of sodium chloride depletion, one group of rats received a single injection of gentamicin, 100 mg/kg, while control animals received the gentamicin vehicle. Twenty-four hours later, PCr and UNa/UCr were similar in both groups. CIn was unchanged, but RBF was reduced significantly (12.40 ± 1.33 vs. 16.89 ± 1.24 ml/min). Micropuncture studies revealed that although SNGFR was unchanged, end-proximal and early distal flow rates were increased significantly. End-proximal TFCl was reduced significantly in gentamicin-treated animals when compared to controls (130.7 ± 3.9 vs. 149.5 ± 4.1 mEq/liter). Early distal TFCl was also reduced significantly (32.4 ± 2.0 vs. 44.3 ± 1.4 mEq/liter). In other rats, 24hr after a second injection of gentamicin, PCr and UNa/UCr were increased significantly and both GFR and RBF were reduced significantly. We conclude that the earliest hemodynamic change in gentamicin-induced acute renal failure is a reduction in RBF which precedes any change in GFR. A single dose of gentamicin also impairs proximal bicarbonate and water reabsorption and reduces end-proximal and early distal chloride concentration.Réduction du débit sanguin rénal et de la réabsorption proximale des bicarbonates chez des rats par la gentamicine. Bien qu'une insuffisance rénale aiguë induite par les aminoglycosides se produise fréquemment, on sait peu de choses sur les mécanismes qui altèrent l'hémodynamique rénale. Chez des rats Sprague-Dawley déplétés en sodium traités par de la gentamicine, nous avons mesuré RBF et GFR au début de ce modèle d'insuffisance rénale aiguë néphrotoxique. Après 10 jours de déplétion en chlorure de sodium, un groupe de rats a reçu une injection unique de gentamicine, 100 mg/kg, tandis que les animaux contrôles recevaient le solvant de la gentamicine. Vingt-quatre heures plus tard, PCr et UNa/UCr étaient identiques dans les deux groupes. CIn était inchangé, mais RBF était significativement diminué (12,40 ± 1,33 contre 16,89) ± 1,24 ml/min). Des études en microponction ont révélé que bien que SNGFR soit inchangé, les débits dans l'extrémité du proximal et le début du distal étaient significativement augmentés. TFCl à la fin du proximal était significativement réduit chez les animaux traités par la gentamicine par rapport au contrôle (130,7 ± 3,9 contre 149,5 ± 4,1 mEq/litre). TFCl au début du distal était également significativement réduit (32,4 ± 3,2 contre 44,3 ± 1,4 mEq/litre). Chez d'autres rats, 24 heures après une seconde injection de gentamicine, PCr et UNa/UCr étaient significativement augmentés, et GFR et RBF étaient significativement diminués. Nous concluons que la modification hémodynamique la plus précoce au cours de l'insuffisance rénale aiguë induite par la gentamicine est une diminution de RBF qui précède toute modification de GFR. Une dose unique de gentamicine altère également la réabsorption proximale de bicarbonate et d'eau, et diminue la concentration de chlore à la fin du proximal et au début du distal.

The mechanism of amine inhibition of the photosynthetic oxygen evolving complex: Amines displace functional chloride from a ligand site on manganese

Amines inhibit photosynthetic oxygen evolution by binding to manganese in the oxygen evolving complex. This inhibition is more effective if chloride is absent. Steady-state kinetic analyses show that ammonia and chloride compete for the same site in the oxygen evolving complex; inhibition of oxygen evolution by either chloride depletion or by ammonia addition induces Signal II f, which saturates at high microwave power. These data indicate that chloride is bound at the manganese site in the oxygen evolving complex. We propose that the anion functions as a bridging ligand mediating electron transfer between manganese atoms and perhaps also between manganese and Z, the primary donor to P680.

Metabolic alkalosis in the rat. Evidence that reduced glomerular filtration rather than enhanced tubular bicarbonate reabsorption is responsible for maintaining the alkalotic state.

Maintenance of chronic metabolic alkalosis might occur by a reduction in glomerular filtration rate (GFR) without increased bicarbonate reabsorption or, alternatively, by augmentation of bicarbonate reabsorption with a normal GFR. To differentiate these possibilities, free-flow micropuncture was performed in alkalotic Munich-Wistar rats with a glomerular ultrafiltrate total CO2 concentration of 46.5 +/- 0.9 mM (vs. 27.7 +/- 0.9 mM in controls). Alkalotic animals had a markedly reduced single nephron GFR compared with controls (27.4 +/- 1.5 vs. 51.6 +/- 1.6 nl/min) and consequently unchanged filtered load of bicarbonate. Absolute proximal bicarbonate reabsorption in alkalotic animals was similar to controls (981 +/- 49 vs. 1,081 +/- 57 pmol/min), despite a higher luminal bicarbonate concentration, contracted extracellular volume, and potassium depletion. When single nephron GFR during alkalosis was increased toward normal by isohydric volume expansion or in another group by isotonic bicarbonate loading, absolute proximal bicarbonate reabsorption was not substantially augmented and bicarbonaturia developed. To confirm that a fall in GFR occurs during metabolic alkalosis, additional clearance studies were performed. Awake rats were studied before and after induction of metabolic alkalosis associated with varying amounts of potassium and chloride depletion. In all cases, the rise in blood bicarbonate concentration was inversely proportional to a reduction in GFR; filtered bicarbonate load remained normal. In conclusion, a reduction in GFR is proposed as being critical for maintaining chronic metabolic alkalosis in the rat. Constancy of the filtered bicarbonate load allows normal rates of renal bicarbonate reabsorption to maintain the alkalotic state.