Differences In Buffering Capacity Research Articles

Mixed Ration Silage Containing Tanzania Grass and Babassu By-Products for Dairy Cows

The use of mixed ration silage (MRS) provides animals with a diet formulation that meets their nutritional requirements. This study aimed to evaluate the fermentative profile, losses, chemical composition and in vitro dry matter digestibility of mixed ration silages, including babassu by-products as a feed alternative for dairy cows. A completely randomized design was used, with four treatments and five replications, which were composed of TGS: Tanzania grass silage; MRSS: Tanzania grass silage with corn and soybean meal; MRSF: Tanzania grass silage with corn, soybean meal and babassu flour; and MRSC: Tanzania grass silage with corn, soybean meal and babassu cake. There was a significant difference between MRS and TGS (p < 0.05) in the variables’ pH, gas (GL) and effluent losses (EL), dry matter recovery (DMR), water-soluble carbohydrates (WSC), dry matter (DM), crude protein (CP) and total digestible nutrients (TDN). There was no statistical difference in buffer capacity (BC), acid detergent lignin, hemicellulose, ether extract (EE) and aerobic stability. However, for the variables’ ammonia nitrogen (NH3-N) and non-fibre carbohydrate (NFC) content, lower values were observed in the MRS (p < 0.001). The babassu by-products, cake and flour, can replace corn by up to 50% of the total ration silage with Tanzania grass, meeting the nutritional requirements of dairy cows.

Imaging Sample Acidification Triggered by Electrochemically Activated Polyaniline.

In this letter, we demonstrate 2D acidification of samples at environmental and physiological pH with an electrochemically activated polyaniline (PANI) mesh. A novel sensor–actuator concept is conceived for such a purpose. The sample is sandwiched between the PANI (actuator) and a planar pH optode (sensor) placed at a very close distance (∼0.50 mm). Upon application of a mild potential to the mesh, in contrast to previously reported acidification approaches, PANI releases a significant number of protons, causing an acid–base titration in the sample. This process is monitored in time and space by the pH optode, providing chemical imaging of the pH decrease along the dynamic titration via photographic acquisition. Acidification of samples at varying buffer capacity has been investigated: the higher the buffer capacity, the more time (and therefore proton charge) was needed to reach a pH of 4.5 or even lower. Also, the ability to map spatial differences in buffer capacity within a sample during the acid–base titration was unprecedentedly proven. The sensor–actuator concept could be used for monitoring certain analytes in samples that specifically require acidification pretreatment. Particularly, in combination with different optodes, dynamic mapping of concentration gradients will be accessible in complex environmental samples ranging from roots and sediments to bacterial aggregates.

Peculiarities of the Physicochemical Properties of Hydrated C60 Fullerene Solutions in a Wide Range of Dilutions

Hydrated fullerene C60 (HyFn) is a supramolecular object in which the nanosized fullerene molecule is enclosed in a multilayer shell of water molecules. Despite the fact that fullerene C60 is chemically rather inert, aqueous solutions of HyFn exhibit a wide spectrum of biological activity in particular in low and ultra-low concentrations. Thus, physical and chemical properties of aqueous solutions of HyFn in a wide range of its dilutions are of interest. Here we compared some physical and chemical properties of aqueous systems prepared by successive 100-fold dilutions of HyFn (10–7 M) with deionized water, with their intensive shaking at each stage up to the calculated HyFn concentration of 10–31 M and of the corresponding “dilutions” of deionized water prepared in the same manner (controls). We studied the character of рН changes in dilutions when titrating them with HCl and NaOH. It turned out that HyFn dilutions had significantly higher buffering capacity against acidification with HCl than control water “dilutions.” At the highest acidity reached pH in all HyFn dilutions was almost 0.3 units higher than in the respective controls. Average buffering capacity of HyFn dilutions and water controls when titrated with NaOH did not differ. However, differences in buffering capacity could be seen between consecutive dilutions of HyFn at their titration either with NaOH or with HCl. Most prominent differences were observed between consecutive HyFn dilutions in the range of calculated concentrations 10–17–10–31 M titrated with NaOH while no significant differences in pH between equivalent “dilutions” of control water were observed. Similar though less prominent variations in buffering capacity between consecutive HyFn dilutions titrated with HCl were also noticed. Thus, titration with an acid and especially with an alkali made it possible to reveal differences between individual dilutions of HyFn, as well as differences between HyFn dilutions and corresponding dilutions of water. These features may be due to complexity in the structural properties of aqueous systems, which, supposedly, can arise due to the emergence of heterogenous aqueous regions (“clouds”) in the course of their dilutions with intensive mixing at each stage. In order to find out if such heterogeneity is a characteristic for HyFn dilutions we used the method of drying microsphere-containing droplets, whose aqueous base were either HyFn dilutions in the range of calculated HyFn concentration 10–7–10–31 M or respective water controls. It was found that a significant part of HyFn dilutions is characterized by mesoscopic heterogeneity. It showed up by the tendency of microspheres to concentrate in a specific way resembling ornaments once the droplets had dried. As the degree of HyFn dilution increased, the number of dried droplets with an ornament-like microsphere distribution increased. Same was also observed in water control drops. However, for the dilutions of HyFn equivalent to concentrations 10–19–10–31 M the percentage of complexly structured dried up droplets reached 60–80%, while for dried out drops of respective water controls it did not exceed 15–20%. Thus, the physicochemical properties of high dilutions of hydrated fullerene differ not only from each other dependently on the dilution level, but also from those of high dilutions of water, which can be explained by the structuredness and heterogeneity of these aqueous systems. Therefore, upon dilution process the properties of the solutions change according to complex and non-linear laws so that final dilutions cannot be identical in their properties and features to those of the initial solutions (before dilutions process) and to the untreated water. Dilution process, in view of the aforementioned, should not be underestimated when analyzing properties of the solutions, having shown to be able to affect dramatically properties of the solutions.

Changes in saliva characteristics and carious status related to metabolic control in patients with type 2 diabetes mellitus

ObjectivesThis cross-sectional study aimed: 1) to compare the saliva characteristics and the occurrence of caries in patients with type 2 diabetes mellitus (T2DM) and patients without T2DM, 2) to study the impact of inadequate glycemic control on saliva and caries prevalence. Methods23 adults with T2DM and 18 controls participated. Patients with T2DM were divided depending on their metabolic control: a) well-controlled (W.C.): HbA1c≤7 %, and b) poorly-controlled (P.C.): HbA1c> 7 %). The examined clinical parameters were: 1) number of natural teeth, 2) DMFT index of coronal caries, 3) saliva pH, 4) saliva flow and buffering capacity, and 5) subjective feeling of dry mouth. ResultsThe groups W.C and P.C showed significant differences in the number of teeth, the saliva flow, and DMFT. The C and P.C groups presented differences in pH, saliva flow, buffer capacity, and DMFT. Finally, the W.C and C groups indicated differences in the buffer capacity, saliva flow, and DMFT. The subjective feeling of dry mouth is related to the duration of the disease. The DMFT value correlated negatively with the status of metabolic regulation. Multiple linear regression revealed that the DMFT value was positively associated with serum HbA1c levels. Conclusions1) Adults with T2DM present a lower saliva flow rate and buffering capacity, as well as higher caries prevalence than controls; 2) The metabolic control of T2DM is essential for the maintenance of saliva flow rate and buffering capacity, and caries prevalence; 3) The duration of T2DM is of importance for the subjective sense of dry mouth. Clinical significanceThe duration and metabolic control of T2DM are important clinical parameters for oral complications. Awareness and co-operation of diabetologists and dentists are needed to detect oral lesions in patients with diabetes and be treated timely and effectively.

ORAL MANIFESTATIONS IN 50 PATIENTS WITH CHRONIC KIDNEY DISEASE ON HEMODIALYSIS: CLINICAL AND SALIVARY ANALYSIS

Objectives: To characterize the oral health of patients with chronic kidney disease (CKD) by evaluating salivary flow, pH, and salivary buffering capacity, oral aspects, gingival bleeding, calculus, index of decay, and missing and filled teeth. Study Design: The present cross-sectional, observational, analytical study reviewed the clinical and demographic data of patients with CKD (n = 50) and compared this data with those who do not have CKD (n = 20). The χ2 test and Fisher exact test was used for association between categorical variables. The Mann-Whitney U test was applied to compare the groups. The level of significance was set at 5%. Results: A total of 56% of patients presented with breath uremic, 69.5% had visible dental calculi, and 26% had another lesion. There was a statistically significant difference between salivary flow and pH in the group with CKD and the control group, but there was not a significant difference in buffering capacity. Conclusion: Oral conditions of the patients were considered precarious, which must be minimized, because these patients are potential transplant candidates. Therefore, having a dentist on the team assisting patients with CKD is paramount.

Validation of the Siggaard-Andersen Acid-Base Nomogram for Hemoglobin F: Implications for Fetal Cord Blood Gas Analysis.

The calculation of HCO3 and base excess in current blood gas analysis is based on the Siggaard-Andersen equation. One of the constants in this equation is dependent on the known buffering capacity of hemoglobin A. We sought to investigate differences in buffering capacity between adult hemoglobin A and fetal hemoglobin F as a potential explanation for the observed poor correlation between calculated base excess in umbilical cord blood and newborn outcomes. Such differences would influence a key constant in the Van Slyke/Siggaard-Andersen equation used to calculate HCO3 and base excess and could be an explanation of these observations. This was a prospective observational study. We analyzed umbilical cord blood bicarbonate levels both as calculated values from a traditional blood gas analyzer and as measured values in 20 women giving birth at term. Since the calculated value is dependent upon the concentration and known buffering capacity of hemoglobin A, significant differences in these two analyses would imply differences in the buffering capacity of hemoglobins A and F. The mean calculated HCO3 value was 25 mEq/L (25.3 ± 1.9) compared with a mean measured value of 25 mEq/L (24.6 ± 1.7) over a range of pH levels of 7.16 to 7.42. This difference was not significant (p = 0.07). The buffering capacity of hemoglobin F, for clinical purposes, is not different than that of hemoglobin A and is not an explanation for the recognized poor correlation between base excess and neonatal outcome.

Assessing the Effects of Climate Change and Air Pollution on Soil Properties and Plant Diversity in Sugar Maple–Beech–Yellow Birch Hardwood Forests in the Northeastern United States: Model Simulations from 1900 to 2100

Historical deposition of nitrogen (N) and sulfur (S) over the Eastern United States has impacted ecosystem structure and function. The potential for recovery of ecosystems is relatively uncertain, with deposition paired with future climate change contributing to this uncertainty. The impacts of N and S deposition and climate change (from 1900 to 2100) on two sugar maple–beech–yellow birch sites in the Northeastern United States were evaluated using the paired biogeochemical–vegetation response model ForSAFE-Veg at two research sites, Hubbard Brook Experimental Forest and Bear Brook Watershed. Deposition was found to be the dominant stressor, causing changes in soil acid–base chemistry, N enrichment, and shifts in understory species composition. Responses of the two sites varied due primarily to differences in buffering capacity and levels of deposition. However, at both sites, recovery of soil and plant community properties to 1900 conditions was approached only when future deposition to 2100 was returned to pre-industrial levels. Policy-based reductions in deposition generally halted further damage to soils and plants and resulted in no or only partial recovery. Increased temperatures and precipitation according to Intergovernmental Panel on Climate Change (IPCC) climate futures stimulated soil and plant response, thereby accelerating changes in plant communities and N enrichment and counteracting the acidifying impacts of N and S deposition on soil acid–base chemistry.

Diatom assemblages and limnological variables from 40 lakes and ponds on Bathurst Island and neighboring high Arctic islands

AbstractWe examined the influence of catchment geology, specifically differences in buffering capacity, on the limnological characteristics and surface sediment diatom assemblages from lakes and ponds from Bathurst Island, High Arctic Canada. Differences in buffering capacity exist on Bathurst Island due to a geological gradient that spans from carbonate‐bearing limestone in the east, to more stable quartz sandstone, siltstone, and shale in the west. We collected physical and chemical limnological data, as well as surface sediment diatom assemblages from nine ponds on the poorly buffered western portion of the island and combined these observations with a previously published dataset of 31 lakes and ponds, from the well‐buffered eastern region. The addition of these nine ponds expanded the pH gradient of the existing Bathurst Island dataset (pH 8.0–8.6) to pH 6.8–8.6. A regional, weighted average diatom‐inferred pH model was developed and showed strength similar to other Arctic calibration sets (, root‐mean‐squared‐error of prediction (RMSEP) = 0.298). Given the links between climate and pH shifts in the High Arctic, the ability to reconstruct pH should be a valuable tool for future paleolimnological studies.

Ambient fecal reactive oxidative species (ROS) buffering capacity as a function of geography and habitual diet: A comparison of rural and urban Guatemalan subjects

BackgroundIn the ambient state, fecal matrix has a powerful capacity to buffer ROS induction in an in situ assay system.ObjectivesTo examine factors influencing the buffering capacity of stools across differing dietary habits, with emphasis on dietary fiber (DF), and between sexes.MethodsAmbient stool samples were collected on 2 nonconsecutive days in 20 rural women (RW) and 20 urban women (UW), with concurrent 24‐h recalls, and on 3 consecutive days in 27 urban men (UM). An assay for Fe‐induced adducts of salicylic acid in mg/mL units gauged fecal buffering. Stool non‐heme Fe was measured by a colorimetric test.>ResultsRW consumed 2.5 X the DF as UW: 40±21 vs 16±8 g, p<0.001, but ROS generation was identical across areas: 0.077±0.015 vs 0.078±0.019 mg/mL, p=0.86. UM had ROS levels 150% higher than women: 0.20±0.11 mg/mL, p<0.0001. Fecal non‐heme Fe associated poorly with ROS production, r=−0.05 (p=0.71), and failed to explain sex difference in buffering capacity.>ConclusionHigh and low DF intakes have no influence on ROS buffering in women, but sex strongly determines ambient oxidative quenching in stools. The latter could explain gender disparities for certain intestinal diseases.Funded by Hildegard Grunow Foundation

Phase-Selective Electroprecipitation of Calcium Phosphate Thin Films at Physiological Temperatures

A protein-compatible combination of temperature and pH conditions allows for phase-selective electrosynthesis of bonelike calcium phosphate materials. The procedure involves an acidic aqueous electrolyte at 20−40 °C for an electroprecipation reaction based on nitrate reduction. X-ray diffraction and Raman spectroscopic data confirm that hydroxyapatite (Ca10(PO4)6(OH)2) is the kinetically preferred phase under galvanostatic electroprecipitation conditions with lower phosphate concentrations (∼0.03 M) in the electrolyte, whereas brushite (CaHPO4·2H2O) is favored when electrolytes with higher phosphate concentrations are used. Titration data suggest that the origin of this concentration-dependent phase selectivity is related to differences in buffering capacity of the electrolytes in the immediate vicinity of the working electrode surface, which explains the variability in phases in previous reports of calcium phosphate electrosynthesis. Critical parameters for controlling film formation are galvanostatic control of the electroprecipitation (for local pH changes that trigger deposition), phosphate concentration (to regulate buffering effects), and the presence of ammonia and ammonium ions in the bulk electrolyte (for complexing to improve film coverage and uniformity).

Characterization of the Human Upper Gastrointestinal Contents Under Conditions Simulating Bioavailability/Bioequivalence Studies

This study was conducted to compare the luminal composition of the upper gastrointestinal tract in the fasted and fed states in humans, with a view toward designing in vitro studies to explain/predict food effects on dosage form performance. Twenty healthy human subjects received 250 mL water or 500 mL Ensure plus (a complete nutrient drink) through a nasogastric tube and samples were aspirated from the gastric antrum or duodenum for a period up to 3.5 h, depending on location/fluid combination. Samples were analyzed for polyethylene glycol, pH, buffer capacity, osmolality, surface tension, pepsin, total carbohydrates, total protein content, and bile salts. Following Ensure plus administration, gastric pH was elevated, buffer capacity ranged from 14 to 28 mmoL L-1 DeltapH-1 (vs. 7-18 mmol L-1 DeltapH-1), contents were hyperosmolar, gastric pepsin levels doubled, and surface tension was 30% lower than after administration of water. Post- and preprandial duodenal pH values were initially similar, but slowly decreased to 5.2 postprandially, whereas buffer capacity increased from 5.6 mmol L-1 DeltapH-1 (fasted) to 18-30 mmol L-1 DeltapH-1 (p<0.05). Postprandial surface tension in the duodenum decreased by >30%, bile salt levels were two to four times higher, luminal contents were hyperosmotic, and the presence of peptides and sugars was confirmed. This work shows that, in addition to already well characterized parameters (e.g., pH, and bile salt levels), significant differences in buffer capacity, surface tension, osmolality, and food components are observed pre-/postprandially. These differences should be reflected in test media to predict food effects on intralumenal performance of dosage forms.

Influence of dissolution medium buffer composition on ketoprofen release from ER products and in vitro–in vivo correlation

The purpose of this work was to investigate the influence of dissolution medium composition on the in vitro release of ketoprofen from a series of ER products and the impact of the different buffer media on the in vivo–in vitro (IVIV) relationship. The products investigated were coated micro bead preparations having increasing levels of coating to retard drug release. Four common dissolution media; USP phosphate buffers of pH 7.2 and 6.8, phosphate (modified isotonic) buffer pH 6.8 and a fasted state simulated intestinal fluid without lipid components (FaSSIFLF) of pH 6.5, were employed in the USP 2 apparatus. Release profiles were compared to the corresponding in vivo release profiles, obtained following deconvolution of the plasma level versus time profiles obtained from a 10-subject five-period cross-over study. Despite the relative similarity in composition of the media employed, significant differences in release profiles were observed reflecting media differences in buffer capacity, ionic strength and pH. As a consequence, the quality and shape of the IVIV relationship changed significantly, the only apparent IVIVC incorporating all four ER products, which was non-linear, was obtained using the phosphate (modified isotonic) buffer of pH 6.8. This data was fitted, using a non-linear least squares method, by the equation of Polli et al. [J. Pharm. Sci. 85 (1996) 753] and gave an alpha parameter estimate of 2, consistent with initial dissolution being more rapid in vitro than in vivo. The systematic shift in profiles, particularly with buffer capacity, underlines the sensitivity of IVIV relationship to medium composition and hence the current difficulties in making a rational choice of an appropriate single dissolution medium.

Foam stability and buffering capacity in cultivars of lucerne (alfalfa)

When lucerne is used for making silage it is prone to developing inferior quality because of a high pH. When lucerne is directly grazed by livestock it is prone to causing bloat, which can be lethal for individual animals. This project examined whether there are cultivar differences in buffering capacity and hence silage-making quality, and in foam stability in leaf extracts and hence the likely persistence of foam in the digesta of the animal. If differences exist, it should be possible either to choose cultivars that are less prone to these problems or to genetically select for superior silage-making and low bloat potential properties using the superior cultivars. Leaf extracts from 12 lucerne cultivars were screened for foam stability, and 32 cultivars were screened for buffering capacity. There were significant differences between 3 cultivars (Sceptre, Aurora and Cimarron) for foam stability, and between 4 cultivars (PL 55, SARDI 66, Trifecta and Oro) for buffering capacity. There was sufficient variation in both characteristics to warrant testing the inclusion of these traits in a lucerne breeding program. All the cultivars tested for silage pH had an unacceptably high pH, even those with lower buffering capacities. This indicated that it would be inappropriate to promote the existing low buffering capacity cultivars as suitable for silage, and that further selection for lower buffering capacity is needed.

In Situ Conservation of Wild Chiles and Their Biotic Associates

Wild congeners of domesticated crops increasingly serve as sources of genes for improving crop cultivars. Although wild congeners have been included in seed collections for ex situ storage, there has been little work to protect populations of these wild species in their natural habitats for in situ conservation. We assessed the distribution of chile plants (Capsicum annuum L. var. aviculare[Dierbach] D’Arcy and Eshbaugh) relative to the dominant woody vegetation of one subpopulation in a single drainage in southern Arizona, U.S.A. Wild chiles were not found in direct sun, and the distribution of chiles under different nurse plants could be a function of random chance, microenvironmental differences under different nurse‐plant species, or nonrandom dispersal by chile consumers. To examine chile distribution, we measured the association of wild chiles with nurse‐plant species and compared these associations with the available cover provided by each nurse plant. We also measured the buffering capacity of each nurse‐plant species, conducted mammalian and avian food‐preference experiments to determine the taxa dispersing chiles, and conducted time‐budget studies of potential chile dispersal agents. Wild chiles were not randomly distributed: over 75% were under the canopies of fleshy‐fruited shrubs that collectively made up less than 25% of the cover. We found limited evidence that differences in buffering capacity affected chile distribution. Food‐preference experiments suggested that birds are the only effective dispersal agents, and the time budgets of three common bird species were strongly correlated with chile plant distribution. These results lend support for directed dispersal by avian consumers. The distribution of chiles appears to be a function of interactions between consumers, nurse plants, and the secondary chemicals in the chiles themselves. Only through studies of in situ populations can we understand the interactions that sustain both wild‐crop relatives and the genetic variability essential to future crop management.

Mobility of heavy metals as a function of pH of samples from an overbank sediment profile contaminated by mining activities

Parts of the flood plains north of the Harz Mountains are contaminated with heavy metals, such as Pb, Cu, Zn and Cd derived from mining, which has been carried out in the Harz Mts. since the Middle Ages. It is important to know the mobility of the heavy metals in these overbank sediments in order to estimate the danger to the environment arising from this source. This paper deals with the effect of pH on heavy-metal mobility, using a constant-pH method. The investigations were carried out on an overbank sediment profile near Salzgitter Bad, north of the Harz Mts. The mobility of the heavy metals in the overbank sediment profile is described as a function of pH and depth. Besides the mobile heavy-metal fraction at a certain pH, the buffering capacity of the sediment at this pH must be taken into consideration. The different layers of the overbank sediment profile show distinct differences in buffering capacity and a natural pH harrier could be identified in the upper part of the profile. Therefore, to avoid increasing heavy-metal mobility the natural layering of the overbank sediment profile should not be disturbed. Two different kinds of desorption experiments at constant pH are also discussed, as well as the conversion of the heavy-metal species in the ore minerals into the species in the sediment.

Identification of a sodium-bicarbonate symport in human platelets

Intracellular pH (pH i) was measured in human platelets using fluorescent probes. Basal pH i was higher in HCO 3 −-buffered solutions (7.33 ± 0.01) than in nominally HCO 3 − free, Hepes-buffered solutions (7.16 ± 0.01, P < 0.05). Addition of EIPA caused a fall in Hepes, but did not inhibit the increase of pH i when platelets maintained in Hepes were transferred to a CO 2 HCO 3 − buffer. After an intracellular acidosis induced by an NH 4Cl prepulse, the initial velocity of recovery ( d(pH) dt i , in pH units/min) was 3.32 ± 0.69 in Hepes-buffered solution and 2.85 ± 0.88 in HCO 3 − media. Taking into account the differences in buffer capacity, the efflux of acid equivalents after 1.2 min was twice as much in the presence of bicarbonate. The addition of 30 μ mol 1 EIPA effectively blocked acid efflux (d(pH)/d t i = 0.08 ± 0.04) in a nominally HCO 3 −-free solution, whereas the recovery was reduced but not abolished (d(pH)/d t i = 0.37 ± 0.10, P < 0.05) in the presence of bicarbonate. The stilbene derivative SITS further inhibited the EIPA-resistant pH i recovery. Removal of external Na + inhibited the HCO 3 −-dependent recovery whereas depletion of internal Cl −, did not suppress it. Depolarization of the membrane had no effect on this recovery. The results suggest the contribution of an electroneutral Na + HCO 3 − cotransport in the recovery of pH i following an acid load. Both the Na + H + antiport and the HCO 3 −-dependent mechanism contribute approx. 50% each to the total acid equivalent efflux during the recovery from a pH i6.46 ± 0.14 to the basal pH i in human platelets.

Cerebral acid buffering capacity at different ages measured in vivo by 31P and 1H nuclear magnetic resonance spectroscopy.

Cerebral acidosis occurring during ischemia has been proposed as one determinant of tissue damage. Newborn animals appear to be less susceptible to ischemic tissue damage than adults. One possible component of ischemic tolerance could derive from maturational differences in the extent of acid production and buffering in newborns compared to adults. The purpose of this study was to measure the dependency of acid production on the blood plasma glucose concentrations and acid buffering capacity of piglets at different stages of development. Complete ischemia was induced in 29 piglets ranging in postconceptual age from 111 to 156 days (normal term conception, 115 days). Brain buffering capacity during the first 30 min of ischemia was quantified in vivo, via 31P and 1H nuclear magnetic resonance (NMR) spectroscopy, by measuring the change in intracellular brain pH for a given change in the concentration of compounds that contribute to the production of hydrogen ions. Animals from all four age groups showed a similar linear correlation between preischemia blood glucose concentration and intracellular pH after 30 min of ischemia. For each animal the slope of the plot of intracellular pH versus cerebral buffer base deficit was used to calculate the buffer capacity. Using data obtained over the entire 30 min of ischemia, there was no difference in the mean buffer capacity of the different age groups, nor was there a significant correlation between buffer capacity and age. However, there was a significant increase in buffer capacity for the intracellular pH range 6.6-6.0, compared to 7.0-6.6, for all age groups. No significant differences in buffer capacity for these two pH ranges were observed between any of the age groups. Acid buffering capacity was also measured by performing pH titrations on brain tissue homogenized in the presence of inhibitors of glycolysis and creatine kinase. Plots of homogenate pH versus buffer base deficit showed a nonlinear trend similar to that seen in vivo, indicating an increase in buffer capacity as intracellular pH decreases. A comparison of newborn and 1-month-old brain tissue frozen under control conditions or after 45 min of ischemia revealed no differences that could be attributed to age and a slight decrease in buffer capacity of ischemic brain compared to control brain tissue homogenates. There was no difference between the brain buffering capacity measured in vivo using 31P and 1H NMR and that measured in vitro using brain homogenates.

Axial heterogeneity of rabbit proximal tubule luminal H+ and basolateral HCO3- transport

The present in vitro microperfusion study examined whether the rates of the apical membrane Na+-H+ antiporter and basolateral membrane Na(HCO3)3 symporter vary along the length of the proximal tubule. Initial proximal convoluted tubules (PCT obtained within 0.5 mm from the glomerulus), mid-PCT (PCT without glomerular attachments) and cortical proximal straight tubules were examined. The rate of either the apical or basolateral membrane acidification mechanism was measured from the initial rate of change of intracellular pH after a change in either the luminal or bathing solution. Intracellular pH was measured fluorometrically using the pH-sensitive dye (2',7')-bis(carboxyethyl)-(5,6)-carboxyfluorescein. The rate of bicarbonate exit across the basolateral membrane was examined by imposing either a sodium or bicarbonate gradient. There was no difference between initial and mid-PCT, but the rate of change in cell pH was 30% slower in PST in both series. The rate of sodium-dependent apical proton secretion was examined by changing the sodium concentration in the lumen. There was no difference in sodium-dependent apical proton secretion in initial vs. mid-PCT, but the rate fell by 70% in the proximal straight tubule (PST). These differences were not due to a difference in buffer capacity in these segments. These data are consistent with a homogeneous rate of apical Na+-H+ antiporter and basolateral Na(HCO3)3 activity along the rabbit PCT, but a lower rate in the PST.

Effects of acids on forest trees as measured by titration in vitro, inheritance of buffering capacity in Picea abies

The effect of acid precipitation on vegetation is the result of an interaction between acid and plant. The metabolism of plants is dependent on optimal pH-values, which are maintained by regulation. There are differences in the effectiveness of regulation under such exogenous influences as acidic precipitation. These differences can be related to the resistance of plants to acidic precipitation. Such differences were measured as buffering capacity of homogenized leaves during titration with acid. There are significant differences in buffering capacity between clones in Pinus spp. and Picea abies. A highly significant variance in buffering capacity also was found among families of P. abies. Calculations of genetical parameters show that the phenotypical variance of buffering capacity is governed mainly by genetical factors.

Respiratory properties of blood and responses to diving of the platypus, Ornithorhynchus anatinus (shaw)

1. 1. Th O 2Hb dissociation curve for platypus blood shows a typical sigmoid shape with a pronounced Bohr effect. 2. 2. The O 2 capacity for one specimen was 23.5 vol % with a corresponding hematocrit of 50 per cent. 3. 3. The blood displayed a considerable Haldane effect and a large difference in buffer capacity between reduced and oxygenated blood. 4. 4. Arterial. blood samples taken during experimental submersion were analyzed for O 2 and CO 2 pressure and content. CaO 2 falls rapidly during diving and reaches a low of 2 vol % after approximatelyt 3 min, which was close to the endurance limit during experimental conditions. A quick restoration of arterial O 2 saturation characterized the recovery. 5. 5. Platypous showed a distinct bradycardia upon submersion. The rate of decline in heart rate was more pronounced if the arterial blood pressure increased in response to submersion. 6. 6. The findings are discussed in relation to the normal diving habits of the platypus.