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PubMed1982

[Barbital buffer in tablets as a solvent for complement fixation test (CFT)].

The purpose of this paper was to develop a tableting technology of barbital buffer as a standard diluent easy in use for complement fixation test (CFT). As starting point, barbital (veronal) buffer after Alton et al. [1] was assumed. Among 4 solubilizers polyvinyl pyrrolidone (PVP 10 000) was chosen, which provided a good solubility of the barbital in distilled water at 20 degrees C and it affected favourably the complement activity (C'). PVP 10 000 added to the components of barbital buffer at an amount of 0.275 per 10 tablets, in the form of solution for granulation, provided the required physical properties of the tablets. As compared with the barbital buffer after Alton et al. [1], the tablets produced affected favourably C' activity, decreased the range of spontaneous haemocyte lysis, and they did not effect CFT titers of two anti-Brucella abortus standard sera as well as 77 sera of cattle infected with brucellosis under natural conditions. The described physical and biological properties of the barbital buffer tablets with PVP addition indicate their usability as diluent for CFT. A standard diluent used in the form of tablets in all Poland's laboratories should provide a better reproducibility of CFT results in diagnostic examinations towards brucellosis as well as other infectious diseases in men and animals.

Animals↗
PubMed1980

Two new non-barbiturate buffers for electrophoresis of serum proteins on cellulose acetate membranes.

Two new non-barbiturate buffers have been formulated for serum protein electrophoresis on cellulose acetate membranes. Both buffers give five distrinct fractions and are suitable for all systems, but have been primarily designed to meet the needs of the Gelman "Sepratek" system. One buffer is a tris(hydroxymethyl)aminomethane (Tris)/hippurate formulation; the other is composed of Tris/N-[tris(hydroxymethyl)methyl]glycine (Tricine)/sodium chloride/sodium salicylate. Both buffers allow reliable quantitation of protein fractions, giving results that correlated well with those obtained from barbiturate separations. The major advantage of these buffers is that they do not contain drugs of abuse.

Barbiturates↗
PubMed1994

The influences of the buffer capacity of various substances on pH changes in dental plaque.

This study clarified the suitable pKa value for buffering substances against plaque pH fall in vitro and simultaneously estimated the effect of low molecular chitosan (LMCS) on plaque pH lowered by metabolized acids in vitro and in vivo. Five buffering substances with different pKa, aspartame (pKa: 7.8), phosphate buffer (7.1), LMCS (6.4), maleate buffer (6.2), and monofluorophosphate (4.8), were tested in this study. In the method using S. mutans cells, phosphate inhibited the pH fall from an initial pH of over 7.0, but phosphate exhibited no effect when the initial pH was 6.0. By the addition with lactic acid, LMCS and maleate exhibited more effective inhibition of the pH-fall than the others. These observations imply that pKa value is an important indicator of the ability of a buffering substance to reduce pH fall in dental plaque and that the optimum pKa value may be around pH 6.3. In the plaque pH measurement using ISFET electrode, LMCS showed an additional effect in inhibiting plaque pH fall following direct application of the glucose solution. The findings indicate that LMCS may be useful as a food additive to decrease the cariogenicity of foods.

Adult↗
PubMed1997

Impact of cytoplasmic calcium buffering on the spatial and temporal characteristics of intercellular calcium signals in astrocytes.

The impact of calcium buffering on the initiation and propagation of mechanically elicited intercellular Ca2+ waves was studied using astrocytes loaded with different exogenous, cell membrane-permeant Ca2+ chelators and a laser scanning confocal or video fluorescence microscope. Using an ELISA with a novel antibody to BAPTA, we showed that different cell-permeant chelators, when applied at the same concentrations, accumulate to the same degree inside the cells. Loading cultures with BAPTA, a high Ca2+ affinity chelator, almost completely blocked calcium wave occurrence. Chelators having lower Ca2+ affinities had lesser affects, as shown in their attenuation of both the radius of spread and propagation velocity of the Ca2+ wave. The chelators blocked the process of wave propagation, not initiation, because large [Ca2+]i increases elicited in the mechanically stimulated cell were insufficient to trigger the wave in the presence of high Ca2+ affinity buffers. Wave attenuation was a function of cytoplasmic Ca2+ buffering capacity; i.e., loading increasing concentrations of low Ca2+ affinity buffers mimicked the effects of lesser quantities of high-affinity chelators. In chelator-treated astrocytes, changes in calcium wave properties were independent of the Ca2+-binding rate constants of the chelators, of chelation of other ions such as Zn2+, and of effects on gap junction function. Slowing of the wave could be completely accounted for by the slowing of Ca2+ ion diffusion within the cytoplasm of individual astrocytes. The data obtained suggest that alterations in Ca2+ buffering may provide a potent mechanism by which the localized spread of astrocytic Ca2+ signals is controlled.

Animals↗
PubMedDate not supplied

Effects of acidity, glucose degradation products, and dialysis fluid buffer choice on peritoneal solute and fluid transport in rats.

OBJECTIVE: To evaluate the effects of acidity, glucose degradation products (GDP), and different solution buffer systems on solute and fluid transport during acute peritoneal dialysis (PD) in rats. DESIGN: Dialysis fluid (16 mL) containing 2.5% glucose as the osmotic agent was instilled intraperitoneally in Wistar rats (280 g) via a thin catheter in dwells lasting 4 hours. Blood and dialysis fluid samples (25 microL) were taken for measurement of glucose, sodium, and radioactive markers. The mass transfer area coefficient (MTAC or PS) for glucose and for 51Cr-EDTA (given as an intravenous infusion) and the peritoneal clearance (Cl) of 125I albumin (RISA), as well as the clearance of RISA to plasma (Cl --> P) were assessed for a commercial, heat-sterilized, acidic PD solution (2.5% glucose, pH 5.5; Gambrosol, Gambro, Lund, Sweden), containing GDP, and for four filter-sterilized solutions containing either lactate (40 mmol/L, pH 5.5 or 7.2), bicarbonate (38 mmol/L, pH 7.2), or pyruvate (40 mmol/L, pH 7.2) as buffers and being devoid of GDP. RESULTS: The initial pH of the acidic solutions increased rapidly, and attained physiological levels within 40 minutes. The initial drop of sodium, which is expected during the first part of the dwell, was significantly more pronounced with neutral than with acidic lactate. The PS for glucose and 51Cr-EDTA were slightly, but significantly, higher with the acidic and heat-sterilized solution (Gambrosol) than with the neutral, sterile-filtered lactate-buffered solution (p < 0.01), especially early during the dwell. Such an increase may be due to initial vasodilatation, and hence, recruitment of capillaries by the combination of acidity and GDP. However, there were no significant differences with respect to small solute PS values among sterile-filtered solutions, regardless of the presence of acidity or of buffer choice. CONCLUSION: There were no major differences in fluid and solute transport among sterile-filtered PD solutions having differing buffer systems and pH. Neither were there any effects of GDP alone. However, the combination of a low pH and the presence of GDP in the PD solutions seemed to cause significant increases in peritoneal small solute transport.

Animals↗
PubMed1998

Evaluation of buffering capacity and acid neutralizing-pH time profile of antacids.

The antacid properties of seven antacids listed in the hospital formulary of a medical center were evaluated with in vitro tests. These included not only the preliminary antacid test and acid-neutralizing capacity test as described in the United States Pharmacopeia (USP XXIII), but also a buffering pH profile test. The preliminary antacid test measured the final pH of a 10-mL solution of 0.5 N HCl 10 minutes after addition of the minimum recommended dose of an antacid, while the neutralizing capacity test measured the amount (mEq) of HCl neutralized by the minimum recommended dose in 15 minutes. The buffering pH profile recorded the pH time course of dynamic simulated gastric fluid neutralization by a dose of an antacid. In the preliminary antacid test, magnesium oxide showed the highest pH (9.52 +/- 0.14, mean +/- standard deviation, n = 3); aluminum phosphate gel yielded a final pH of 2.51 +/- 0.01, thus failing to meet the criteria of an antacid (pH > 3.5). In the acid-neutralizing capacity test, hydrotalcite had the highest neutralizing capacity (28.26 +/- 0.3 mEq), while sodium bicarbonate had the lowest (7.40 +/- 0.12 mEq). In the buffering pH profile test, aluminum-magnesium hydroxide suspensions and hydrotalcite tablets maintained a steady optimum pH (3-5) for around 1.5 hours. One tablet of calcium carbonate, sodium bicarbonate or magnesium oxide could not raise the gastric pH to above 3, but two tablets increased the pH excessively (5.3 to 8.6). The higher dose (two tablets) of aluminum hydroxide hexitol complex could not raise the pH to the optimal level. These findings demonstrate that there is disparity in the antacid effectiveness estimated by the neutralizing capacity test and the buffering pH profile test and suggest that the efficacy of an antacid cannot be accurately predicted from its acid-neutralizing capacity. The dose of antacids greatly influences the neutralizing pH profiles. Aluminum-magnesium compounds appear to provide steadier buffering than carbonate compounds or magnesium oxide.

Aluminum Compounds↗
PubMed2000

Enhanced image detail using continuity in the MIP Z-buffer: applications to magnetic resonance angiography.

In this paper a new algorithm is presented for the segmentation and display of blood vessels from images obtained with magnetic resonance angiography (MRA) and other three-dimensional (3D) angiographic imaging techniques. The algorithm developed is based on the observation that vessels are strongly evident in the maximum intensity projection (MIP) Z-buffer as regions of high continuity and low local roughness. Roughness is measured here by the minimum chi2 value of a low-order local least-squares fit in the principal directions through each point in the MIP Z-buffer. Although some background pixels in the Z-buffer exhibit low local roughness, the size of the connected region is nearly always much smaller than even the very smallest vessels that appear in the MIP image. It is shown that by applying connectivity to the regions of low roughness, there is nearly complete separation between vascular detail and background. When connectivity is further applied in the original 3D image, vascular bed segmentation becomes nearly complete. The algorithm consists of three basic steps: a) determination of the minimum local roughness at each point in the MIP Z-buffer; b) connection of all neighboring points of low local roughness; and c) connection of all points in the original 3D image matrix that are connected to the points determined in the MIP Z-buffer and that are above an intensity threshold. The algorithm as presented is not optimized but demonstrates a very strong potential for improved portrayal of vascular detail.

Algorithms↗
PubMed2000

From genotype to phenotype: buffering mechanisms and the storage of genetic information.

DNA sequence variation is abundant in wild populations. While molecular biologists use genetically homogeneous strains of model organisms to avoid this variation, evolutionary biologists embrace genetic variation as the material of evolution since heritable differences in fitness drive evolutionary change. Yet, the relationship between the phenotypic variation affecting fitness and the genotypic variation producing it is complex. Genetic buffering mechanisms modify this relationship by concealing the effects of genetic and environmental variation on phenotype. Genetic buffering allows the build-up and storage of genetic variation in phenotypically normal populations. When buffering breaks down, thresholds governing the expression of previously silent variation are crossed. At these thresholds, phenotypic differences suddenly appear and are available for selection. Thus, buffering mechanisms modulate evolution and regulate a balance between evolutionary stasis and change. Recent work provides a glimpse of the molecular details governing some types of genetic buffering.

Animals↗
PubMed1990

Effects of temperature and buffer composition on calcium sequestration by sarcoplasmic reticulum and plasma membrane of rabbit renal artery.

45Ca electron microscopic autoradiography was used to examine the effects of buffer composition and temperature on the distribution of calcium in rabbit renal artery smooth muscle cells. The results show that the relative distribution of calcium is dependent on both the buffer used (Tris or Krebs) and the temperature of the bathing solution (25 degrees C or 34 degrees C). Krebs buffer at 34 degrees C gave the highest relative activity in the plasma membrane, sarcoplasmic reticulum, and mitochondria. Buffer and temperature had little effect on the relative activity of the nucleus or cytoplasm. Next, we identified the cellular sites of calcium accumulation after 5, 15, 30, or 60 min exposure to 45Ca in Krebs buffer at 34 degrees C. The results show that sarcoplasmic reticulum and plasma membrane are the primary sites of calcium accumulation during influx into these cells. Although the amount of 45Ca in the cell continues to increase with longer exposure, the relative distribution of calcium is essentially the same after 5 or 60 min. The data also indicate that the relative activity of plasma membrane + sarcoplasmic reticulum (a combination site that includes sarcoplasmic reticulum within a mean distance of 275 nm of the plasma membrane) is similar to the membrane alone and is lower than the sarcoplasmic reticulum alone.

Animals↗
PubMed1989

Relations between slow extracellular potential changes, glial potassium buffering, and electrolyte and cellular volume changes during neuronal hyperactivity in cat brain.

The aim of this investigation is to estimate the contribution of spatial glial K+ buffer currents to extracellular K+ homeostasis during enhanced neuronal activity. Neuronal hyperactivity was induced by electrical stimulation of the cortical surface or the ventrobasal thalamic nuclei of cats (5-50 Hz, 0.1-0.2 ms, two to three times threshold stimulation intensity, 5-20 s). The accompanying slow field potential changes were recorded simultaneously across the grey matter with vertical assemblies of eight micropipettes glued 300 microns apart. Using the Poisson equation, the amplitudes of the underlying current sources and sinks were calculated. The current source densities depended on the depth of recording, frequency, strength, and duration of the stimulation. Current sinks, corresponding to a removal of 0.1-0.5 mmoles of monovalent cations per liter of brain tissue and second from the extracellular space, were observed in middle cortical layers, whereas sources appeared at superficial and deeper sites. These sinks and sources might represent K+ moved across glial membranes by spatial buffer currents. The consequences of glial buffer currents of this magnitude were investigated with model calculations. It turned out that measurements of electrolyte and volume changes of the extracellular space (Dietzel et al. Exp. Brain Res. 40:432-439, 1980; Exp. Brain Res. 46:73-84, 1982) could only partially be explained by spatial buffer currents of this magnitude. Comparison of the calculated values with intracellular measurements in neurons and glial cells (Coles et al. Ann. N.Y. Acad. Sci. 481:303-317, 1986; Ballanyi et al. J. Physiol. 382:159-174, 1987) suggests that spatial buffering combines with an approximately equimolar KCl transport and, depending on the preparation, also K+/Na+-exchange across glial membranes.

Action Potentials↗
PubMed2003

Phosphate buffers in capillary electrophoresis/mass spectrometry using atmospheric pressure photoionization and electrospray ionization.

Capillary electrophoresis (CE) has been combined with atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) for mass spectrometric (MS) detection. Separation conditions using potassium phosphate buffer and ammonium formate buffer have been compared for analysis of eleven pharmaceutical bases. The results showed improvements in separation efficiency and peak symmetry when phosphate buffer was used. The low flow in CE may enable utilization of these advances with MS detection. Compared with ESI, the APPI technique provided a cluster-free background. The enhanced signal-to-noise ratio in the total ion current (TIC) and the reduced spectral background indicated that the APPI process is less affected by non-volatile salts in the CE buffers. This results in a wider range of choice of CE buffers in CE/MS analysis when APPI is the ionization method.

Journal Article↗
PubMed1998

Buffer zones for reducing pesticide drift to ditches and risks to aquatic organisms.

Pesticide drift from field sprayers fitted with different types of spray nozzles was investigated under various wind speed conditions. Droplet drift was measured adjacent to the sprayed field, on the ditch bank, and in the ditch. Measurements were carried out in the normal sprayed situation and with an unsprayed buffer zone 3 or 6 m wide. The results indicate that there are major differences between spray nozzles. Drift deposition increases with wind speed. In the sprayed situation and with a wind speed of 0.5 m/s, there was a maximum of 6.0% drift deposition halfway down the ditch bank and no drift deposition in the ditch. At 3 m/s wind speed these figures are 25.1 and 2.2%, respectively. At 5 m/s wind speed, 7.2% drift deposition was measured in the ditch. Risk assessment (cf. SLOOTBOX model) carried out with 17 pesticides used in the study area indicated that at this wind speed, 8 of the 17 pesticides investigated posed a risk to aquatic organisms. Creation of a 3-m buffer zone decreases drift deposition in the ditch by a minimum of 95%. Adjacent to the buffer zone only 4 of the 17 pesticides investigated posed a (minor) risk to aquatic organisms. With a 6-m buffer zone no drift deposition in the ditch could be measured (wind speed maximum, 4.5 m/s). Creating unsprayed crop edges offers good possibilities for the protection of aquatic ecosystems. Socioeconomic research among farmers indicates that buffer zones, such as unsprayed cereal edges and unsprayed grass strips, could well be adopted in agricultural practice.

Agriculture↗
PubMed1995

Determination of resting free calcium in barnacle muscle using modified aequorins, buffered calcium injections, and simultaneous image-intensified video microscopy.

Knowing the resting free calcium is important in understanding the role of calcium as an intracellular second messenger. We used a bracketing (null) technique with a luminescent calcium indicator, aequorin, microinjection and image-intensification to measure free calcium in single muscle fibres from the barnacle, Balanus nubilus. We injected modified aequorins (recombinant, and hch-) which after a 30 min diffusion gave reasonable resting glows. Subsequent injection of calcium (strongly buffered with either EGTA or BAPTA, 10 mM) increased or decreased the resting glow depending on the free calcium level in the injected buffer solution. This bracketing (null) method is inherently accurate, but mechanical artifacts on calcium injection reduce the accuracy when total light emission is measured. We therefore used image-intensified video-microscopy of the injected region and video processing (Image-1) of artifact-free regions, to greatly improve the consistency. The luminescence in a pre-selected region of the muscle fibre was measured as a function of time during the injection. Solution calciums were chosen so that if the first injection decreased the resting glow, the second increased it, or vice versa, thus bracketing the true resting value. We used two methods to determine the true value bracketed by our injections: (1) a linear interpolation using the fractional changes in luminescence or (2) a power law interpolation assuming a 2.2 or 2.5 power relationship between luminescence and free calcium. Using these methods, we estimated the free calcium level in the lateral depressor fibres of freshly dredged barnacles to be 279 +/- 36 nM (+/- SD), 339 +/- 42 nM, or 352 +/- 45 nM for the linear, 2.2 and 2.5 powers respectively under the conditions of hch-aequorin and BAPTA buffers (using a K'Ca for BAPTA of 3.0 x 10(6) M-1 for our conditions). Recombinant-aequorin gave essentially the same result while EGTA buffers yielded a somewhat higher value but because of influences of pH on the K'Ca for EGTA (taken as 6.7 x 10(6) M-1 for our conditions) was considered less reliable. Minor changes in [Mg2+] upon buffer injection can lead to underestimates of the true resting [Ca2+] by at most 10%. Thus, we estimate the resting free calcium in barnacle muscle fibres to be 300-380 nM.

Aequorin↗
PubMed1990

Muscarinic cholinergic receptor mediated inhibitory transduction of adenylate cyclase activity in subcellular fractions from rat heart: improved detection in sodium phosphate buffer.

Cholinergic inhibition of myocardial adenylate cyclase activity in cell-free fractions has been known for many years, although the reported degrees of inhibition have been rather modest (20-30%), notably in rat heart fractions. The present study conducted with rat heart subcellular fractions document following major findings: (1) Myocardial adenylate cyclase activity and notably its cholinergic inhibition in cell-free fractions are notoriously labile to storage at 4 degrees C whereas its stimulation by beta adrenergic receptor agonists or forskolin are reasonably well preserved during storage. (2) Among four buffers (Tris, glycylglycine, imidazole and sodium phosphate) examined, sodium phosphate buffer afforded the best preservation of cholinergic inhibitory response of adenylate cyclase. (3) The commonly used biochemical buffers, notably imidazole, exerted deleterious effect on the cholinergic inhibition of myocardial adenylate cyclase such that it was considerably attenuated or barely detectable; this explains, in part, the reported poor inhibition of myocardial enzyme by others. (4) Imidazole buffer, on the other hand, augmented beta adrenergic and forskolin stimulated adenylate cyclase activity. The likely significance of these findings is discussed from consideration that the observed differential influence of buffers results from differential actions on the interactions between the components (receptor/coupling G proteins/catalyst) comprising autonomic receptor coupled adenylate cyclase system in rat heart.

Adenylyl Cyclases↗
PubMed1985

Ca2+ buffer sites in intact bovine rod outer segments: introduction to a novel optical probe to measure ionic permeabilities in suspensions of small particles.

The nature of the Ca2+ buffer sites in intact rod outer segments isolated from bovine retinas (ROS) was investigated. The predominant Ca2+ buffer in intact ROS was found to be negatively charged groups confined to the surface of the disk membranes. Accordingly, Ca2+ buffering in ROS was strongly influenced by the electrostatic surface potential. The concentration of Ca2+ buffer sites was about 30 mM, 80% of which were located at the membrane surface in the intradiskal space. A comparison with observations in model systems suggests that phosphatidylserine is the major Ca2+ buffer site in ROS. Protons and alkali cations could replace Ca2+ as mobile counterions for the fixed negatively charged groups. At physiological ionic strength, the total number of these diffusible, but osmotically inactive, counterions was as large as the number of osmotically active cations in ROS. The surface potential is dependent on the concentration of cations in ROS and can be measured with the optical dye neutral red. Addition of cations to the external solution led to the release of the internally bound dye as the cations crossed the outer membrane. The chemical and spectral properties of the dye enable its use as a real-time indicator of cation transport across the outer envelope of small particles in suspension. In this study, the dye method is illustrated by the use of well-defined ionophores in intact ROS and in liposomes. In the companion paper this method is used to describe the cation permeabilities native to ROS.

Animals↗
PubMed2005

Assessing protected area effectiveness using surrounding (buffer) areas environmentally similar to the target area.

Many studies are based on the assumption that an area and its surrounding (buffer) area present similar environmental conditions and can be compared. For example, in order to assess the effectiveness of a protected area, the land use/cover changes are compared inside the park with its surroundings. However, the heterogeneity in spatial variables can bias this assessment: we have shown that most of the protected areas in Mexico present significant environmental differences between their interior and their surroundings. Therefore, a comparison that aims at assessing the effectiveness of conservation strategies, must be cautioned. In this paper, a simple method which allows the generation of a buffer area that presents similar conditions with respect to a set of environmental variables is presented. The method was used in order to assess the effectiveness of the Calakmul Biosphere Reserve, a protected area located in the south-eastern part of Mexico. The annual rate of deforestation inside the protected area, the standard buffer area (based upon distance from the protected area only) and the similar buffer area (taking into account distance along with some environmental variables) were 0.3, 1.3 and 0.6%, respectively. These results showed that the protected area was effective in preventing land clearing, but that the comparison with the standard buffer area gave an over-optimistic vision of its effectiveness.

Conservation of Natural Resources↗
PubMed1990

Quantitation of the hepatic arterial buffer response to graded changes in portal blood flow.

Hepatic arterial blood flow changes inversely in response to altered portal blood flow. The hepatic arterial capacity to buffer portal flow changes was studied over a wide range of portal flow with arterial pressure held steady (the active buffer response) or uncontrolled. The active component of the buffer response led to nearly full dilation of the hepatic artery at low portal flows as shown by inability to dilate further in response to adenosine infusion; at high portal flows the hepatic artery was nearly fully constricted as shown by lack of further constriction to norepinephrine. With pressure uncontrolled, active and passive effects combined to produce an increased compensation with similar efficiency (44% +/- 4%) over the full range of portal blood flows. Thus, although the active component of the hepatic arterial buffer response becomes less efficient at very high and low portal flows, the combination of active and passive effects leads to a larger buffer capacity which is equally efficient over a wide range of portal blood flow changes.

Adenosine↗
PubMed1984

Carbon dioxide dissociation and buffering in chicken blood during development.

Carbon dioxide dissociation curves of oxygenated and deoxygenated bloods, the Haldane effect, the buffer value and other blood and true plasma buffering indices, O2 capacity and hematocrit were determined in bloods withdrawn from chicks before, during and after hatching and 8-month-old hens. Blood CO2 dissociation curves shifted upwards in the developing embryo till pipping, and moved downwards after pipping and hatching. In accordance with the position of the CO2 dissociation curves, the true plasma bicarbonate and red cell CO2 standardized to PCO2 = 40 torr changed. The Haldane factor at standard PCO2 increased from 0.12-0.13 on days 10-14 of incubation to 0.34 in young hens. The buffering power changed in parallel with O2 capacity and hematocrit, increasing steadily during incubation, dropping at hatching and then increasing again to the adult value. The observed changes in the CO2 dissociation curves and buffering variables during the development enable the chick to minimize the changes in the acid-base status and are favorable for coping with the increasing demand for CO2 transport and buffering of the developing bird.

Acid-Base Equilibrium↗