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Biomedical subjects

A Bidani

Publications and source records attributed to A Bidani.

At least 91 records · Page 5Linked to original sources
PubMed1991

ATP-sensitive Na(+)-H+ antiport in type II alveolar epithelial cells.

Type II alveolar epithelial cells in suspension have been previously shown to possess a Na(+)-H+ antiporter that modulates recovery from an intracellular acid load in the nominal absence of HCO-3 [E. Nord, S. Brown, and E. Crandall. Am. J. Physiol. 252 (Cell Physiol. 21): C490-C498, 1987]. Such a Na(+)-dependent mechanism has also been demonstrated in cultured type II cell monolayers (K. Sano et al. Biochim. Biophys. Acta 939: 449-458, 1988). It has recently been suggested that cultured type II cells possess a H(+)-ATPase that contributes to recovery from an intracellular acid load [R. Lubman, S. Danto, and E. Crandall. Am. J. Physiol. 257 (Lung Cell. Mol. Physiol. 1): L438-L445, 1989]. The present study was undertaken to investigate and characterize the mechanisms by which cultured type II cells recover from an intracellular acid load in the nominal absence of HCO-3. Cultured type II cell monolayers were loaded with the pH-sensitive probe 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein, and the characteristics of recovery from an imposed intracellular acid load were studied. Recovery of intracellular pH (pHi) was found to be strictly Na(+)-dependent and inhibited greater than or equal to 95% by 1 mM amiloride. Initial rate of recovery was highly sensitive to pHi, with recovery rates varying inversely with increasing pHi. An acidic extracellular pH (6.5) abolished pHi recovery. Treatment of type II cells with either the sulfhydryl reagent N-ethylmaleimide, a nonspecific sulfhydryl reagent, or 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole, a specific vacuolar H(+)-ATPase inhibitor at the concentration tested, resulted in marginal but not statistically significant decrements in pHi recovery. Intracellular ATP depletion, using KCN or replacement of glucose by a nonmetabolizable glucose analogue, reduced pHi recovery by 70-75% relative to control values. Sensitivity to ATP was apparent even under conditions that preserved the transmembrane Na+ gradient. Taken together, these data are most consistent with a single mechanism for pHi recovery in the absence of HCO3-. We interpret this mechanism to be an ATP-sensitive Na(+)-H+ antiporter that acts to reestablish pHi in type II alveolar epithelial cells.

Adenosine Triphosphate↗
PubMed1991

Analysis of abnormalities of capillary CO2 exchange in vivo.

Capillary CO2 exchange in vivo is affected by several interdependent reactions and transport processes. A mathematical model that includes all the significant chemical and transport events that are presumed to occur during capillary gas exchange has been used to investigate the effect of inhibition of 1) erythrocyte HCO(3-)-Cl- exchange, 2) lung carbonic anhydrase (CA) activity with access to plasma, and 3) erythrocyte CA activity on overall pulmonary CO2 excretion (VCO2) during rest and moderate exercise. Any decrement in VCO2 due to inhibition of HCO(3-)-Cl- exchange and/or CA activity, should result in compensatory alterations in cardiac output and/or an increase in the mixed venous blood-to-alveolar PCO2 gradient [(delta PCO2)V-A] to restore steady-state VCO2. Our computations show that complete inhibition of erythrocyte anion exchange would require a compensatory increment in cardiac output of approximately 30-40% or an increase in (delta PCO2)V-A from 6 to 8.3 Torr at rest and from 12 to 15.6 Torr during moderate exercise, if lung CA activity is intact. In the absence of availability of lung CA activity to plasma, the necessary (delta PCO2)V-A is 10.5 Torr at rest and 19.5 Torr during moderate exercise. Complete inhibition of lung and erythrocyte CA activity is predicted to require (delta PCO2)V-A of 39.1 Torr at rest and 74.2 Torr during moderate exercise. These results suggest that HCO(3-)-Cl- exchange might not be vital to maintenance of CO2 transfer and perhaps has a more important role in minimizing the changes in plasma pH associated with microvascular gas exchange in vivo.

Bicarbonates↗
PubMed1991

Effects of perfusate buffer capacity on capillary CO2-HCO3(-)-H+ reactions: theory.

The importance of perfusate nonbicarbonate buffer capacity (beta nonHCO3) to intracapillary CO2-HCO3(-)-H+ reactions was assessed by theoretical analysis of CO2 exchange in saline-perfused pulmonary capillaries. Time courses for perfusate PCO2, [HCO3-], and [H+] were computed for capillaries containing different activities of luminal vascular carbonic anhydrase and different amounts of perfusate nonbicarbonate buffers. Mobilization of perfusate HCO3- toward CO2 during capillary transit is determined by the availability of HCO3- and H+. A supply of protons from the nonbicarbonate buffer pool is necessary to maintain a high rate of HCO3- dehydration. The analyses indicate that beta nonHCO3 has marked nonlinear effects on transcapillary CO2 exchange and intravascular pH equilibration. These nonlinear effects differ from those previously computed for CO2 reactions in an open system because the present model system consists of a sequential combination of open (within capillary proper) and closed (within postcapillary vasculature) systems. The role of luminal vascular carbonic anhydrase in capillary CO2 reactions is strongly dependent on beta nonHCO3. Perfusate nonbicarbonate buffer capacity must be considered when the results of experimental studies of transcapillary CO2 exchange and/or intravascular pH equilibration are interpreted.

Bicarbonates↗
PubMed1991

Interfacial transfer kinetics of NO2 into pulmonary epithelial lining fluid.

Previous studies, both in intact lungs and epithelial lining fluid (ELF) (J. Appl. Physiol. 68: 594-603, 1990 and J. Appl: Physiol. 69: 523-531, 1990), have suggested that the steady-state absorption of inhaled NO2 is mediated by chemical reaction(s) between NO2 and ELF solute reactants. To characterize the kinetics of NO2 absorption into aqueous biological substrates across a gas-liquid interface, we utilized a closed system of known geometry and initial gas phase [NO2] [([NO2]g)0] to expose ELF (as bronchoalveolar lavage; BAL) and a biochemical model system (glutathione, GSH). Assessments of NO2 reactive uptake, into both GSH and ELF, indicated first-order NO2 kinetics [([NO2]g)0 less than or equal to 10.5 ppm] with effective rate constants of (kNO2)GSH = 4.8 and (kNO2)BAL = 2.9 ml.min-1.cm-2 (stirred). Above 10.5 ppm (1 mM GSH), zero-order kinetics were observed. Both (kNO2)GSH and (kNO2)BAL showed aqueous reactant dependence. The reaction order with respect to GSH and BAL was 0.47 and 0.64, respectively. We found no effect of interfacial surface area or bulk phase volume on kNO2. In unstirred systems, significant interfacial resistance was observed and was related to reactant concentration. These results indicate that NO2 reactive uptake follows first-order kinetics with respect to NO2 ([NO2]g less than or equal to 10.5 ppm) and displays aqueous substrate dependence. Furthermore the site of reactive absorption appears to be limited to near the aqueous surface interface. Unstirred conditions confine interfacial mass transfer kinetics in a dose-dependent manner. These phenomenological coefficients may provide the basis for direct extrapolation to environmentally relevant exposure concentrations.

Absorption↗
PubMed1990

The effect of NO2 exposure on perfusate distribution in isolated rat lungs: pulmonary versus bronchial circulation.

Isolated rat lung (IPL) studies have suggested that the pulmonary uptake of inhaled nitrogen dioxide (NO2) is governed via a chemical reaction-dependent process which results in NO2-derived reaction products diffusing into the vascular space. Experimental results indicated that substantial proportions of this reactive absorption occur in distal sites. However, gas phase deposition in proximal locations cannot be ruled out due to the lack of information on bronchial perfusion in rat IPL preparations. Consequently, we evaluated the presence of pulmonary-to-bronchial anastomotic perfusate flow in control and NO2-exposed (10.3 ppm) rat IPL. Monastral blue (MB) was used as a vascular marker and was infused into the pulmonary artery catheter either for recirculation at time zero or as an end-experiment (60 min) bolus. In addition, MB was infused into control in situ preparations to observe intact bronchial circulations. Lungs were prepared for routine evaluation by light microscopy. In situ MB was observed in all pulmonary and bronchial vessels. In IPL, MB was observed only in far terminal airway-associated vessels. No differences were observed in MB distribution between bolus (end-experiment) and recirculated (time zero) applications. NO2 exposure produced no effect on MB distribution. We conclude that in rat IPL: (1) negligible anastomotic flow occurs from the pulmonary into the bronchial circulation, (2) nonedemagenic NO2 exposures do not alter existing perfusate distribution, and (3) the perfusate appearance of inhalation-derived species results from gas phase deposition only in distal sites which have ready accessibility to the pulmonary circulation.

Animals↗
PubMed1990

Kidney transplants in cyclosporine-treated Sprague-Dawley rats.

Previous studies by others have shown that transplanted rat kidneys have abnormally low clearances of paraaminohippuric acid, inulin, and creatinine, due to rejection and/or to warm-ischemia-induced injury. In the present studies, randomly bred Sprague-Dawley rats were used as donors and recipients. The left kidneys of recipients were removed, and the right kidneys were left intact. Donor kidneys were flushed with an ice-cold hypertonic solution (150 mM NaCl, 200 mM mannitol, pH 6.4), and the kidneys were kept cold during surgery. Renal function was assessed 1 week later. The left transplanted kidneys in untreated recipients exhibited morphologic evidence of rejection, and the clearances of PAH and inulin were approximately 50% of those of the right native kidneys. CsA-treated rats did not reject the transplants, and the PAH and inulin clearances of the left transplanted kidneys were identical to those of the right native kidneys. Untreated and CsA-treated rats with both native kidneys intact served as controls. The amount of CsA given during the 7-day period produced no measurable change in renal function. This is the first demonstration of virtually normal hemodynamics in transplanted rat kidneys when randomly bred animals are used as donors and recipients. Moreover, the results indicate that if both rejection and warm ischemia are avoided, the presence of a functioning native kidney does not have a detrimental effect on the function of a transplanted kidney.

Animals↗
PubMed1990

ATP-dependent pHi recovery in lung macrophages: evidence for a plasma membrane H(+)-ATPase.

We have previously shown that cytoplasmic pH (pHi) recovery in pulmonary macrophages, under nominally HCO3(-)-free conditions, after acute intracellular acidification is Na+ and amiloride insensitive and is blocked by nonspecific proton adenosinetriphosphatase (ATPase) inhibitors N-ethyl-maleimide and N,N'-dicyclohexylcarbodiimide [Am. J. Physiol. 257 (Cell. Physiol. 26): C65-C76, 1989]. To further delineate the mechanism of H+ extrusion across plasma membranes of pulmonary macrophages, we investigated the effects of metabolic inhibitors of oxidative phosphorylation and glycolysis on cellular ATP content and pHi recovery from an intracellular acid load under nominally HCO3(-)-free conditions. Dose-dependent reductions in ATP levels and in the rate of pHi recovery were obtained in the presence of KCN (50% inhibition, 10(-4) M). Parallel reductions in ATP content and the rate of pHi recovery were noted in the presence of antimycin A, rotenone, oligomycin, and iodoacetate. However, inhibition by iodoacetate was reduced in the presence of pyruvate. The more specific vacuolar H(+)-ATPase inhibitors, bafilomycin A1 and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole, resulted in no decrement in cellular ATP levels but significantly inhibited pHi recovery. These studies demonstrate that recovery from an acid load is ATP dependent and provide support for a plasmalemmal proton ATPase, perhaps of the vacuolar type, that participates in regulation of pHi in pulmonary macrophages.

4-Chloro-7-nitrobenzofurazan↗
PubMed1990

The role of adenosine in HgCl2-induced acute renal failure in rats.

It has been proposed that adenosine mediates the renal hemodynamic changes in acute renal failure (ARF) and that these changes are pathogenic in reducing glomerular filtration rate. Consistently, adenosine-receptor antagonists such as theophylline have been shown to have protective effects in several experimental models of ARF. The present experiments were designed to explore the potential role of adenosine in HgCl2-induced ARF in rats. In isolated perfused rat kidneys, HgCl2 increased adenosine production and induced a concentration-dependent vasoconstriction. However, the vasoconstriction was unrelated to adenosine production and was not antagonized by theophylline. During the initiation phase of HgCl2-induced ARF in intact rats (first 4 h after injection), theophylline failed to reverse the reduction in inulin clearance, and this failure could not be attributed to a loss of vascular responsiveness to adenosine, since N6-cyclohexyladenosine, a receptor agonist, produced a further reduction in inulin clearance. Furthermore, theophylline actually had deleterious effects during the maintenance phase of HgCl2-induced ARF in intact unanesthetized rats, as evidenced by higher mean serum creatinine values in theophylline-injected rather than in saline-injected rats, on both the second and third days after HgCl2 injection. Therefore HgCl2 acutely increases renal adenosine production, but increased adenosine does not mediate acute HgCl2-induced renal vasoconstriction, and adenosine-receptor antagonism does not have protective effects during the initiation or the maintenance phases of HgCl2-induced ARF in rats. These results provide no support for the hypothesis that increased adenosine mediates the hemodynamic changes in HgCl2-induced ARF.

Acute Kidney Injury↗
PubMed1990

Reactive uptake governs the pulmonary air space removal of inhaled nitrogen dioxide.

With the use of an isolated rat lung model, we investigated pulmonary air space absorption kinetics of the reactive gas NO2 in an effort to determine the contributory role of chemical reaction(s) vs. physical solubility. Unperfused lungs were employed, because vascular perfusion had no effect on acute (0- to 60-min) NO2 absorption rates. We additionally found the following: 1) Uptake was proportional to exposure rates (2-14 micrograms NO2/min; 10-63 ppm; 37 degrees C) but saturated with exposures greater than or equal to 14 micrograms NO2/min. 2) Uptake was temperature (22-48 degrees C) dependent but, regardless of temperature, attained apparent saturation at 10.6 micrograms NO2/min. 3) Lung surface area (SA) was altered by increasing functional residual capacity (FRC). Expanded SA (8 ml FRC) and temperature (48 degrees C) both raised fractional uptakes (greater than or equal to 0.81) relative to 4 ml FRC, 37 degrees C (0.67). Uptake rates normalized per unit estimated SA revealed no independent effect of FRC on fractional uptake. However, temperature produced a profound effect (48 degrees C = 0.93; 4 and 8 ml FRC = 0.54). 4) Arrhenius plots (ln k' vs. 1/T), which utilized derived reactive uptake coefficients (k'), showed linearity (r2 = 0.94) and yielded an activation energy of 7,536 kcal.g-1.mol-1 and Q10 of 1.43, all consistent with a reaction-mediated process. These findings, particularly the effects of temperature, suggest that acute NO2 uptake in pulmonary air spaces is, in part, rate limited by chemical reaction of NO2 with epithelial surface constituents rather than by direct physical solubility.

Air Pollutants↗
PubMed1990

Reactive absorption of nitrogen dioxide by pulmonary epithelial lining fluid.

In a previous study (J. Appl. Physiol. 68: 594-603, 1990) in isolated rat lungs, we suggested that the rate of pulmonary air space absorption of inhaled NO2 is limited, in part, by chemical reaction(s) rather than by physical solubility. Because the initial site of primary absorption interactions involves the epithelial lining fluid (ELF), we investigated whether ELF-NO2 interactions could account for pulmonary NO2 reactive absorption. Rat ELF, obtained by bronchoalveolar lavage (BAL), was compared with a model chemical system (reduced glutathione, GSH). In vitro exposures (NO2-air) used constant gas flow and planar gas-liquid interfaces. 1) Solvent pH notably altered NO2 uptake by GSH but to a lesser extent by BAL. 2) Uptake displayed [GSH]-dependent saturation. [ELF] in BAL was augmented by sequential lavage (lavagate reuse) of multiple lungs. Uptake was proportional to [ELF] but did not saturate under these exposure conditions. 3) The uptake rate exhibited [NO2] dependence. However, relative to increasing [NO2], fractional uptakes decreased for BAL and 1 mM GSH but not for 10 mM GSH. 4) Altered convective gas flow produced nonlinear increments in uptake (10 mM GSH) and substantial decrements in fractional uptake. 5) Arrhenius plots [ln(r) vs. 1/T, where r is reaction rate and T is absolute temperature (degree K)] for BAL and 1 mM GSH yielded respective activation energies of 4,952 and 4,149 kcal.g-1.mol-1 and degree of change in the rate of NO2 uptake per 10 degrees C (Q10) of 1.32 and 1.25. These results imply that the rate of NO2 uptake into rat ELF, like intact lung, is limited, in part, by chemical reaction(s).(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1990

In situ characterization of carbonic anhydrase activity in isolated rat lungs.

Lung carbonic anhydrase (CA) participates directly in plasma CO2-HCO3(-)-H+ reactions. To characterize pulmonary CA activity in situ, CO2 excretion and capillary pH equilibration were examined in isolated saline-perfused rat lungs. Isolated lungs were perfused at 25, 30, and 37 degrees C with solutions containing various concentrations of HCO3- and a CA inhibitor, acetazolamide (ACTZ). Total CO2 excretion was partitioned into those fractions attributable to dissolved CO2, uncatalyzed HCO3- dehydration, and catalyzed HCO3- dehydration. Approximately 60% of the total CO2 excretion at each temperature was attributable to CA-catalyzed HCO3- dehydration. Inhibition of pulmonary CA diminished CO2 excretion and produced significant postcapillary perfusate pH disequilibria, the magnitude and time course of which were dependent on temperature and the extent of CA inhibition. The half time for pH equilibration increased from approximately 5 s at 37 degrees C to 14 s at 25 degrees C. For the HCO3- dehydration reaction, pulmonary CA in situ displayed an apparent inhibition constant for ACTZ of 0.9-2.2 microM, a Michaelis-Menten constant of 90 mM, a maximal reaction velocity of 9 mM/s, and an apparent activation energy of 3.0 kcal/mol.

Acetazolamide↗
PubMed1990

Cytoplasmic pH recovery in acid-loaded haemocytes of squid (Sepioteuthis lessoniana).

Cytoplasmic pH (pHi) of haemocytes of bigfin reef squid (Sepioteuthis lessoniana Lesson) was determined with the fluorescent probe, 2',7'-biscarboxyethyl-5,6-carboxyfluorescein (BCECF). The pHi of haemocytes suspended in nominally HCO3(-)-free medium (extracellular pH 7.4) averaged (+/- S.E.) 7.32 +/- 0.02. Intracellular pH was independent of external Na+ concentration and varied only slightly with changes in extracellular pH (pHe) (delta pHi/delta pHe = 0.16 over the pHe range 6.8-7.8). Addition of weak acids (sodium propionate, potassium acetate) to haemocyte suspensions resulted in a rapid decrease in pHi. Haemocyte pHi then recovered with an average half-time of 3-4 min. Recovery of pHi was independent of external Na+ concentration and insensitive to amiloride, but was abolished by N-ethylmaleimide (NEM). These results argue against the involvement of plasma membrane Na+/H+ exchange or other Na(+)-dependent transport mechanisms in the pHi recovery of acid-loaded haemocytes. The results suggest that there is an NEM-sensitive proton extrusion mechanism in the plasma membrane of squid haemocytes.

Acid-Base Equilibrium↗
PubMed1990

Dipyridamole inhibition of HCO3(-)-Cl- exchange in human erythrocytes.

Effects of dipyridamole (DP) on Band 3-mediated HCO3(-)-Cl- exchange were investigated in human red cells at 37 degrees C. The kinetics of net HCO3(-)-Cl- exchange were monitored using a stopped-flow rapid reaction apparatus, under conditions in which HCO3(-)-Cl- exchange was rate-limiting for pH equilibration across the red cell membrane. DP was found to be a rapidly acting, potent inhibitor of HCO3(-)-Cl- exchange, with an apparent I50 of 4 microM. DP produced a mixed competitive-noncompetitive inhibition of HCO3-Cl- exchange. Greater than 50% of the inhibitory effect occurred within 20 msec of DP-red cell interaction, consistent with DP binding to an outward-facing site on the cell membrane. Interaction of red cells with DP was associated with a pH-dependent decrement in the equilibrium Donnan H+ ratio. Because HCO3(-)-Cl- exchange is crucial in vivo for ensuing rapid pH equilibration across the red cell membrane, these effects of DP may have important implications, particularly in the development of high-dose DP regimes for use as an adjunctive agent in cancer chemotherapy.

Bicarbonates↗
PubMed1989

Acute renal failure.

Although a wide variety of disease processes can result in a failure of renal excretory function, the vast majority of cases with "acute renal failure" (ARF) are due to the syndrome of acute tubular necrosis (ATN). The syndrome is usually initiated by an acute injury to the proximal renal tubular epithelial cells by ischemic or nephrotoxic events. This is followed by progressive and often rapid increases in the concentration of blood urea nitrogen (BUN) and serum creatinine. In the average case, the failure of renal excretory function persists for 1 to 3 weeks, to be followed by recovery. Oliguria (urine volume less than 400 ml) is present in about half of the patients. The pathogenesis of the retention of nitrogenous waste in human ATN is the subject of controversy, but the balance of data in most patients suggests that the predominant mechanism is a profound secondary vasoconstriction in response to tubular cell injury. This may represent a teleologically appropriate response to prevent catastrophic losses of fluid that would occur, if the normally high rates of glomerular filtration continued, in the face of reduced tubular reabsorptive capacity. The mechanisms by which the tubular cell injury is communicated to the vasculature, and the mediators of the hemodynamic changes, remain to be established. The differential diagnosis in a patient with ARF, usually involves exclusion of an obstruction to the urinary tract as an initial step. The next step is to differentiate the patients with ATN from those who have renal hypoperfusion in response to events in the systemic circulation, but who otherwise have functionally and structurally intact kidneys, i.e., prerenal ARF. The kidneys of patients with prerenal ARF exhibit the normal renal response to an acute reduction in renal blood flow and glomerular filtration rate (GFR). This consists of avid reabsorption of the filtered salt and H2O, so that a small amount of concentrated and NaCl-poor urine is elaborated. The tubular cell injury in ATN syndromes prevents this response from maximally occurring, so that the urine is isosmotic and relatively rich in NaCl.

Acute Kidney Injury↗
PubMed1989

Pulmonary disposition of inhaled NO2-nitrogen in isolated rat lungs.

Nitrogen dioxide (NO2) is a relatively insoluble, reactive gas that, on inhalation, generates a diverse array of pulmonary toxic effects. Its uptake and transformation in isolated lungs have been shown to be proportional to inspired dose and associated with significant accumulations of the nitrite ion. However, not all absorbed NO2 is directly detectable as soluble nitrite. To further characterize its uptake and chemical disposition, we determined the chemical fate of 15NO2-nitrogen in isolated perfused (red cell-free) rat lungs that were exposed to 20 ppm 15NO2 for 60 min. Total excess 15N (relative to unexposed controls) was determined by isotope ratio mass spectrometry and total nitrogen analysis. Excess 15N was detected in whole lungs and in soluble and insoluble fractions but not in the total lipid pool. Perfusate excess 15N and nitrate correlated and accounted for all absorbed NO2 not detectable in tissue fractions. Exogenously instilled [15N]nitrite distributed within lung tissue, bound to insoluble elements, and diffused to the vascular space similar to NO2-nitrogen. Instilled [15N]nitrate did not distribute or bind like NO2-nitrogen or nitrite. Dialysis (1000 molecular weight cutoff) of cytosol, membranes, and perfusate removed excess 15N and nitrite derived from NO2, nitrite, or nitrate sources. We conclude that in isolated lungs, inhaled NO2 (1) undergoes rapid uptake and transformation in sites accessible to the pulmonary circulation; (2) does not form stable addition products with lipids; and (3) forms small-molecular-weight soluble reaction product(s) that behave similarly to nitrite, most likely indicating predominant univalent reduction of NO2 via initial hydrogen abstraction and subsequent HNO2 dissociation.

Administration, Inhalation↗
PubMed1989

Cytoplasmic pH in pulmonary macrophages: recovery from acid load is Na+ independent and NEM sensitive.

The pulmonary macrophage plays a primary role in the immunological defense of the lung. Although many studies have been devoted to elucidation of its phagocytic and secretory functions, little is known of its membrane transport properties or of how it regulates intracellular pH (pHi). The purpose of this study, therefore, was to determine base-line pHi and the mechanism(s) by which the cell recovers pHi when challenged with an intracellular acid load. Through the use of the pH-sensitive fluorescent dye, 2,7-biscarboxyethyl-5(6)-carboxy-fluorescein (BCECF), base-line pHi was estimated to be 7.24 +/- 0.03. Cells were acidified by two methods, nigericin and weak acids, while recovery (dpHi/dt) was monitored. The rate of recovery was found to be independent of external Na+ and K+ and was insensitive to amiloride. Pretreatment with 4,4'-diiso-thiocyanatostilbene-2,2'-disulfonic acid, an inhibitor of Cl- -HCO3- exchange, was also without effect on recovery from an intracellular acid load in these cells, under nominally HCO3- -free conditions. In contrast, N-ethylmaleimide (NEM) and N,N'-dicyclohexylcarbodiimide, nonspecific inhibitors of proton adenosinetriphosphatases (ATPases), virtually abolished pHi recovery. Efflux of H+ equivalents by pulmonary macrophages was measured by techniques involving both pH stat titration and the effect on fluorescence of extracellular BCECF. Basal H+ extrusion was approximately 2.75 +/- 0.64 nmol H+.min-1.10(6) cells-1 and was enhanced to approximately 26.0 +/- 6.95 nmol H+.min-1.10(6) cells-1 in acid-loaded cell suspensions. The basal rate of H+ extrusion was reduced to approximately 0.84 +/- 0.31 nmol H+.min-1.10(6) cells-1 in the presence of 1 mM NEM. These results suggest that recovery of cytoplasmic pH from an intracellular acid load, as well as regulation of pHi, under the conditions examined, is not mediated by a Na+-H+ exchanger in these cells. Rather, the data are consistent with the presence of an H+-ATPase in the plasma membrane of pulmonary macrophages.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1988

Velocity of CO2 exchanges in the lungs.

As outlined above, investigations over the past decade have provided further insight into the kinetics of many of the component processes that affect the overall velocity of CO2 exchanges in the lungs. The evolution of our understanding of the importance and role of these reactions and transport processes has not been entirely predictable. A variety of investigations into Roughton's original hypothesis regarding the mechanism of pH equilibration in capillary blood resulted in a renewed interest in carbonic anhydrase in the lung and other tissues. These latter studies have helped better define the location and kinetic properties of lung CA and its role in the overall velocity of CO2 exchange. Concurrently, a wealth of information has emerged regarding the transport properties of the red cell membrane. This has led to a better understanding of the mechanisms and characteristics of the band 3-mediated pathway for electroneutral anion exchange. Unfortunately, most of the kinetic data for this pathway have been obtained under nonphysiological conditions, making it difficult to utilize them directly in analyses of lung CO2 exchange kinetics. The potential detrimental effect of pharmacological agents in modifying lung CA and red cell CA activity and red cell anion exchange kinetics is among the more important factors to have emerged in the past decade. Ironically, the original question of whether a significant blood pH disequilibrium is present in the arterial circulation in man in vivo remains unresolved. However, the mechanisms underlying these phenomena are now recognized to be more complex than originally appreciated.

Animals↗