Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Buffers”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44Linked to original sources
PubMed1993

31P NMR studies of rat liver cold preservation with histidine-buffered lactobionate solution.

The efficiency of a preservation medium, histidine-buffered lactobionate solution (HBLS), was determined by measuring post-ischemic recoveries of ATP and intracellular pH under Krebs-Henseleit buffer (KHB) perfusion. We used NMR spectroscopy to study the effect of 24-h cold ischemia, followed by 4 degrees C then 37 degrees C reperfusion on the isolated rat liver. Three media were compared: University of Wisconsin solution (UW-lactobionate); Bretschneider's solution (HTK); HBLS and HBLS supplemented with 2 mM Gly and 2 mM Cys (HBLSg2) or with 10 mM Gly and 2 mM Cys (HBLSg10). All values were compared to control values measured during pre-ischemic cold perfusion with KHB (ATP = 8.60 +/- 0.6 mumol/g of dry weigh and pH(in) = 7.41 +/- 0.05). The main result from 31P NMR data concerned ATP recovery during cold reperfusion, which was significantly higher in the HBLS group (112 +/- 10%) as compared to the UW and HTK groups (around 66%). The presence of glycine decreased ATP recovery (88 +/- 8% in HBLSg2, 79 +/- 15% in HBLSg10). Higher values of recovered pHin were observed in livers stored in histidine buffered solutions (around 7.30) as compared to UW (around 7.20); histidine was by 13C NMR proved to accumulate in the liver cells, thus ensuring a good buffering capacity. The thermal transition induced a decrease in both ATP level and pHin in all groups. This might be the result of a stimulation of the carbohydrate metabolism (as demonstrated by 13C NMR) especially when glycine was present in the storage solution.

Adenosine↗
PubMed1998

Cytosolic pH variations in perfused rat liver at 4 degrees C: role of intracellular buffering power.

The effect of low temperature on cytosolic pH regulation and buffering capacity was evaluated in the isolated rat liver. The pH changes were followed by phosphorus-31 nuclear magnetic resonance. Cooling from 37 to 4 degrees C, with Krebs-Heinseleit perfusion at an external pH of 7.35, induced an alkaline shift in cytosolic pH (pHcyt) of 0.13 or 0.75 pH units in the presence of bicarbonate, respectively (dpH cys/dT values were 0.004 and 0.022 unit/degrees C. With 4 degrees C perfusion, in the presence or absence of bicarbonate, acute changes of external pH (from 7.40 to 5.90) did not affect pHcyt. In contrast, intracellular loading with isobutyric acid or NH4Cl induced rapid pHcyt variations. The intrinsic buffering power value (10 to 50 slykes) measured in the absence of bicarbonate depended on pHcyt. The larger value was observed for pHcyt 7.30, a value near the pK value of the imidazole group of intracellular proteins at 4 degrees C. The presence of bicarbonate modified the amplitude of the pHcyt change by increasing the total buffering power. It was demonstrated that during hypothermia, ionic carriers are inactivated and the charged forms of molecules are unable to cross the cell membrane; thus, the pHcyt homeostasis depends essentially on intracellular buffering power.

Acidosis↗
PubMed1989

How phosphocreatine buffers cyclic changes in ATP demand in working muscle.

1. Spatial buffering is hardly necessary for maintaining ATP concentration. 2. Temporal buffering may be essential to defend concentration of products of ATP hydrolysis. ADP would vary 4-fold and AMP would vary 16-fold during a single twitch without buffering. 3. The principal function of the transphosphorylating reaction may be to buffer temporally the concentrations of controlling reactants.

Adenosine Triphosphate↗
PubMed1994

A method for estimating bicarbonate buffering of lactic acid during constant work rate exercise.

A method to estimate the CO2 derived from buffering lactic acid by HCO3- during constant work rate exercise is described. It utilizes the simultaneous continuous measurement of O2 uptake (VO2) and CO2 output (VCO2), and the muscle respiratory quotient (RQm). The CO2 generated from aerobic metabolism of the contracting skeletal muscles was estimated from the product of the exercise-induced increase in VO2 and RQm calculated from gas exchange. By starting exercise from unloaded cycling, the increase in CO2 stores, not accompanied by a simultaneous decrease in O2 stores, was minimized. The total CO2 and aerobic CO2 outputs and, by difference, the millimoles (mmol) of lactate buffered by HCO3- (corrected for hyperventilation) were estimated. To test this method, ten normal subjects performed cycling exercise at each of two work rates for 6 min, one below the lactic acidosis threshold (LAT) (50 W for all subjects), and the other above the LAT, midway between LAT and peak VO2 [mean (SD), 144 (48) W]. Hyperventilation had a small effect on the calculation of mmol lactate buffered by HCO3- [6.5 (2.3)% at 6 min in four subjects who hyperventilated]. The mmol of buffer CO2 at 6 min of exercise was highly correlated (r = 0.925, P < 0.001) with the increase in venous blood lactate sampled 2 min into recovery (coefficient of variation = +/- 0.9 mmol.l-1). The reproducibility between tests done on different days was good. We conclude that the rate of release of CO2 from HCO3- can be estimated from the continuous analysis of simultaneously measured VCO2, VO2, and an estimate of muscle substrate.

Adult↗
PubMed1987

Intracellular pH and buffer power of type 1 and 2 fibres from skeletal muscle of Xenopus laevis.

Intracellular pH (pHi) and buffering power of type 1 and type 2 fibres from the iliofibularis muscle of the clawed frog, Xenopus laevis, have been measured using pH-sensitive microelectrodes. In phosphate buffered Ringer's solution (extracellular pH 7.25, 20-22 degrees C), mean pHi and its variance were similar in the two fibre types (6.86 +/- SD 0.15 +/- SEM 0.03, n = 24, type 1, and 6.86 +/- SD 0.12 +/- SEM 0.03, n = 15, type 2). On changing to Ringer's solution containing CO2 and HCO3- (extracellular pH 7.25, 20-22 degrees C), pHi became more acid in both fibre types. Although H+ ions were not at electrochemical equilibrium across the surface membrane, active transport did not return pHi to its original value during exposure to CO2. The buffering powers calculated from the changes in pHi were not significantly different, 41.6 mmol X l-1 per pH unit (+/- SEM 4.0, n = 17) for type 1 and 49.3 mmol X l per pH unit (+/- SEM 7.2, n = 11) for type 2 fibres. Thus differences in the mechanical properties of these fibre types are not due simply to a difference of the intracellular pH or buffering of resting fibres. Other possible explanations are discussed for the changes in some contractile properties that occur when pHi is acidified.

Animals↗
PubMed1983

Localization of neuronal Ca2+ buffering near plasma membrane studied with different divalent cations.

Absorbance changes associated with divalent cation binding to arsenazo III were used to measure changes in Ca2+, Sr2+, and Ba2+ concentrations under a variety of experimental conditions. The rate of the falling phase of an absorbance change signal, measured in nerve cell bodies injected with arsenazo III and under membrane potential control, was taken as an index of divalent cation buffering. With influx of ions through the membrane or with ionophoretic injection, we found the buffering, i.e., the dye-absorbance signal's falling rate, to be greatest for Ca2+ ions: the sequence was Ca2+ greater than Sr2+ much greater than Ba2+. Injecting Ca2+ or Sr2+ into the center of a nerve cell produced a significantly greater amplitude of arsenazo III signal than the same injection near the cell membrane. We did not find this to be the case for Ba2+ or Mg2+ injections. We conclude that the Ca2+ regulatory system binds Ca2+ most strongly compared to the other ions tested, and there is a variable distribution of buffering machinery within the nerve soma, with increased buffer capacity near the plasma membrane of the cell. A preliminary report of some of the results presented in this paper has appeared previously ( Tillotson and Gorman, 1980).

Animals↗
PubMed1990

Antimony electrodes. Mucosal potential differences and buffer composition adversely affect pH measurements in the stomach.

Antimony electrodes are clinically useful because of their low cost and simple construction; they have no glass to break. There is only a few hundred ohms resistance between an antimony pH electrode and the reference electrode so that the voltage generated can be recorded with simple low-impedance recorders linked to microcomputers. We used antimony pH electrodes with silver-silver chloride electrodes applied to the skin to measure the gastric pH in vivo and obtained erroneously high values. Using an ion-permeable dialysis chamber to surround electrodes in vivo, we showed that the discrepancy was caused by interference from gastric transmucosal potential difference. To circumvent the interference, we used a combination electrode constructed by embedding a monocrystalline antimony electrode and a silver-silver chloride reference electrode in dental acrylic. Antimony pH electrodes calibrated with commercial pH buffers also gave erroneous readings in HCl solutions of known pH. The erroneous readings were due, in part, to organic complex-forming ligands or organic salts such as potassium phthalate present in commercial buffer solutions. Accurate pH calibration can be obtained with citrate or acetate buffers or by using a normogram to correct for the errors introduced with commercial buffers. The combination antimony pH electrode has a number of potential clinical and research applications and simplifies obtaining accurate and reliable pH data in vivo.

Antimony↗
PubMed1983

Plasma levels of acetylsalicylic acid and salicylic acid after oral ingestion of plain and buffered acetylsalicylic acid in relation to bleeding time and thrombocyte function.

Buffered acetylsalicylic acid (Alka Seltzer, B-ASA) and plain aspirin (P-ASA) tablets were compared as to their effects on bleeding time and platelet function in eight healthy male volunteers. Two doses (500 and 1000 mg) of each preparation were investigated in a cross-over design, each volunteer being his own control in each dose group (n=4). Both preparations disturbed platelet aggregation to the same extent. Bleeding time increased after both preparations, though significantly more after the buffered preparation than after plain acetylsalicylic acid, irrespective of the dosage. The 1000 mg dose prolonged bleeding time significantly more than the 500 mg dose, irrespective of the preparation. Kinetic analysis showed that B-ASA gave higher peak plasma levels of acetylsalicylic acid (ASA) and accordingly salicylic acid peak levels were also higher after the buffered preparation. It is concluded that B-ASA in equi-analgesic doses prolongs bleeding time more than the plain preparation. Since it is less agressive on the gastro-intestinal mucosa, its use may be advantageous in situations where acetylsalicylic acid induced loss of platelet aggregation is desired. However, the risk of prolonged bleeding--e.g. after tooth extractions--is probably higher after the buffered preparation.

Adult↗
PubMed1989

Bisphosphonates and extrarenal acid buffering capacity.

Both the intracellular compartment and bone mineral are supposed to play a role in acid-base balance by contributing to the extrarenal acid buffering capacity. Bisphosphonates could affect extrarenal acid buffering capacity by interfering with the formation and/or dissolution of bone mineral. In the present study, rats were pretreated with either 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP, 10 mg/kg.day sc), with prevailing inhibitory action on bone mineral formation, or dichloromethylene bisphosphonate (Cl2MBP, 10 mg p/kg.day sc) with prevailing action on bone resorption, or NaCl injections (controls) for 7 days. In intact rats, blood acid-base variables were influenced by neither HEBP, nor Cl2MBP. Two hours after nephrectomy and before acute acid loading, HEBP-but not Cl2MBP-pretreated rats displayed a significant increase in both blood HCO3- and PCO2. After HCl infusion (2.5 mEq/kg), the relative decrement in blood HCO3- (difference in blood HCO3- before and after acid loading) was transiently more important in the two bisphosphonate pretreated groups than in controls. After a 24 hour fasting period, nephrectomized animals pretreated with Cl2MBP displayed significantly lower blood HCO3- and pH values than controls or HEBP-pretreated rats. These results suggest that bisphosphonates influence extrarenal buffering capacity according to their prevailing inhibitory action on either bone mineral formation and/or dissolution. These compounds could interfere with the release rate of bone proton buffers. However, in the presence of normal renal function, this effect does not disturb the blood acid-base equilibrium.

Acid-Base Equilibrium↗
PubMedDate not supplied

Incorporation of labeled glucosamine into glycoproteins by organ cultures of hamster trachea: adverse effects of HEPES buffer.

Hamster tracheas were cultured in serum-free CMRL 1066 medium buffered with either NaHCO3 alone or HEPES (N-2-hydroxyethylpiperazine-N'-2-ethanesulphonic acid) plus NaHCO3 in an atmosphere of 95% O2 and 5% CO2. Afther 2 days in culture, tracheas maintained in HEPES plus NaHCO3-buffered medium showed an altered surface morphology. Histiological examination after 6 days of culture with HEPES plus NaHCO3 showed the presence of only scattered clumps of cilia. Incorporation of [14C]-glucosamine into intracellular glycoproteins was reduced by 75% and into secreted glycoproteins by 54% in cultures buffered with HEPES plus NaHCO3, compared to NaHCO3-buffered cultures. Incorporation of [H]fucose into intracellular glycoproteins was also reduced, although no effect was observed on secreted glycoproteins.

Animals↗
PubMed1991

Effects of media buffer systems on growth and electrophysiologic characteristics of cultured sweat duct cells.

Primary cultures of human reabsorptive sweat duct cells were grown in MCDB 170 medium buffered with either HEPES, bicarbonate, or a mixture of HEPES and bicarbonate buffers. Cultures grown in MCDB media containing bicarbonate seemed to differentiate into a multilayered, keratinized epithelium and began senescing after 1 wk in culture. In contrast, cultures grown in media containing HEPES as the only buffer seemed to undergo a selection process, resulting in the outgrowth of cells that did not multilayer or keratinize extensively for up to 3 or 4 wk in culture. Despite marked differences in growth, cells grown in both bicarbonate and HEPES-buffered media retained electrophysiologic characteristics appropriate to the progenitor. Mean resting potentials were -21.8 +/- 0.8 mV (n = 82), -23.3 +/- 1.3 mV (n = 70) and -18.2 +/- 0.8 mV (n = 82) for duct cells grown in HEPES, bicarbonate, and HEPES-bicarbonate media, respectively. Substitution of Cl- with the impermeant anion gluconate in the bathing medium caused membrane potential depolarization in all media, revealing the presence of a Cl- conductance. Administration of the Na+ conductance inhibitor amiloride hyperpolarized the mean resting potential of cells grown in HEPES medium (-6.8 +/- 0.6 mV, n = 68), bicarbonate medium (-6.9 +/- 0.5 mV, n = 60), and HEPES-bicarbonate medium (-5.9 +/- 0.6 mV, n = 69), demonstrating expression of a Na+ conductance. We observed some but minimal variation with age in any of these conditions.

Adult↗
PubMed1994

Contribution to the study of the alteration of lipase activity of Candida rugosa by ions and buffers.

A semipurified C. rugosa lipase (LS) has been prepared from commercial lipase (LC) using an economical procedure. The presence of sugars and glycopeptides has been detected in LS and LC. Pure lipase only has covalently bonded sugars. The hydrolysis of olive oil catalyzed by LS and commercial lipase (LC) is sensitive to the presence of cations Na(I), Mg(II), Ca(II), and Ba(II) and to the nature of buffer. Highest enzyme activity is obtained with 0.1M Tris/HCl buffers and the combination of NaCl 0.11M and CaCl2 0.11M. Fluorescence spectroscopy analysis of LC, LS, and both pure isoenzymes lipases A and B, was used to analyze the interaction of the lipase with these effectors. Inorganic cations Na or Ca do not interact with pure enzyme LA but do interact with LC and LS and do so slightly with LB. The organic cations (morfolinium or tris) interact with pure lipases. We postulate that the increase in the lipase activity produced by Na(I) or Ca(II) is related with interfacial phenomena, but the increase might be more specific in the hydrolysis of olive oil in the presence of Tris-HCl or morfoline-HCl buffer, owing to enzyme-buffer interaction.

Buffers↗
PubMed1982

Buffering capacity of the chief components of nutritive media for algae.

The buffering capacity of solutions of KH2PO4 and NaHCO3 increases with their concentration, the behaviour being describable by mathematical expressions. Solutions of KH2PO4 prepared from tap water exhibit a buffering capacity higher by an order of magnitude than those prepared from distilled water. However, there is no difference between the buffering capacities of solutions of NaHCO3 prepared from tap and distilled water. Urea and NH4NO3 have almost no effect on the buffering capacities of solutions.

Bicarbonates↗
PubMed1982

Effect of temperature and pH on absorption of carbon dioxide by a free level of mixed solutions of some buffers.

The rate of absorption of carbon dioxide by solutions of NaHCO3, KH2PO4, hydrogencarbonate, phosphate and borate buffers at 20, 30 and 40 degrees C was determined manometrically. The absorption rate increases for all buffers tested with increasing pH. The CO2 absorption rate by KH2PO4 and by the phosphate buffer at low pH is lower than that of water. For other buffers tested it is equal to or higher than that of water, especially at higher temperatures.

Absorption↗
PubMed1997

Advantage of buffered solutions or automated capnometry in air-filled balloons for use in gastric tonometry.

OBJECTIVE: To test accuracy, reproducibility and time constants of pCO2 measurement with the tonometric technique, using different media for filling the silastic balloon (saline, phosphate buffer, citrate buffer, air) and employing different analyzer devices (ABL3, ABL330, Nova Stat 5, automated capnometry). DESIGN: Comparative laboratory study of different tonometric techniques, measuring test solutions with known pCO2 values due to pre-equilibration with three different pCO2 concentrations. SETTING: Clinical laboratory of a university hospital intensive care unit. MEASUREMENTS AND RESULTS: The use of saline, as suggested for routine tonometry, led to negative bias values throughout, i.e. underestimation of pCO2 values, the extent of which depended on the blood gas analyzer device employed. Registration of the equilibration kinetics showed that full equilibration demanded 90 min regardless of the environmental pCO2 level. Replacing saline by buffered electrolyte solutions resulted in a significant improvement of bias, but did not change the kinetics of pCO2 equilibration. The employment of air-filled balloons, combined with automated capnometry, led to very low bias values, approaching zero, for all pCO2 levels, along with excellent precision. Time constants of equilibration were dramatically reduced, with full equilibration being achieved within 12.5 min. CONCLUSIONS: Buffered electrolyte solutions are preferable to saline for achieving reliable pCO2 measurements in gastric tonometry. Air-filled balloons, combined with automated capnometry, present excellent accuracy and reproducibility together with short equilibration times, thus offering "on-line" monitoring of even rapid changes in environmental pCO2.

Bias↗
PubMed2001

Chromatographic characterization of molecularly imprinted microspheres for the separation and determination of trimethoprim in aqueous buffers.

Molecularly imprinted microspheres (MIMs) against trimethoprim (TMP), prepared by aqueous microsuspension polymerization, bound strongly to TMP, by electrostatic and other non-covalent interactions. The effects of pH, kind and ionic strength (I) of buffer on capacity factors (k') have been discussed in detail. The capacity factors for TMP increased with increasing pH of both acetate and phosphate buffers. The effects of ionic strength on capacity factors were very substantial and the linear relationship between logk' and logI was described by the equation logk'=0.3162-0.4420logI with R=-0.9995. The results showed that pH 3.5 acetate buffer (0.05 mol L(-1)) containing 0.1 mol L(-1) sodium chloride and a 1:9 ratio of buffer to methanol were the optimum conditions for separation and determination of TMP. The calibration plot of peak area against concentration was linear with R=0.9979.

Biosensing Techniques↗
PubMed2000

Intracellular pH regulation and buffer capacity in CO2/HCO3-buffered media in cultured epithelial cells from rainbow trout gills.

The influence of a CO2/HCO3(-)-buffered medium on intracellular pH regulation of gill pavement cells from freshwater rainbow trout was examined in monolayers grown in primary culture on glass coverslips; intracellular pH (pHi) was monitored by continuous spectrofluorometric recording from cells loaded with 2',7'-bis(2-carboxyethyl)-5(6)-carboxy-fluoroscein. When cells in HEPES-buffered medium at normal pH = 7.70 were transferred to normal CO2/HCO3(-)-buffered medium ¿PCO2 = 3.71 mmHg, [HCO3-] = 6.1 mmol l(-1), extracellular pH (pHe) = 7.70¿, they exhibited a brief acidosis but subsequently regulated the same pHi (approximately 7.41) as in HEPES. Buffer capacity (beta) increased by the expected amount (5.5-8.0 slykes) based on intracellular [HCO3-], and was unaffected by most drugs and treatments. However, after transfer to high PCO2 = 11.15 mmHg, [HCO3-] = 18.2 mmol l(-1) at the same pHe = 7.70, the final regulated pHi was elevated (approximately 7.53). The rate of correction of alkalosis caused by washout of this high PCO2, high-HCO3- medium was unaffected by removal of extracellular Cl-. Removal of extracellular Na + lowered resting pHi and greatly inhibited the rate of pHi recovery from acidosis. Bafilomycin A1 (3 micromol l(-1)) had no effect on these responses. However amiloride (0.2 mmol l(-1)) inhibited recovery from acidosis caused by washout of an ammonia prepulse, but did not affect resting pHi, the latter differing from the response in HEPES where amiloride also lowered resting pHi. Similarly 4-acetamido-4'- isothiocyanatostilbene-2,2'-disulfonic acid, sodium salt (0. 1 mmol l(-1)) did not affect resting pHi but slowed the rate of recovery from acidosis, though to a lesser extent than amiloride. Removal of extracellular Cl(-1) also slowed the rate of recovery but greatly increased beta by an unknown mechanism; when this was taken into account, H+ extrusion rate was unaffected. These results are consistent with the presence of Na+ -(HCO3)N co-transport and/or Na+-dependent HCO3(-)/Cl(-) exchange, in addition to Na+/H+ exchange, as mechanisms contributing to "housekeeping" pHi regulation in gill cells in CO2/HCO3(-) media, whereas only Na+/H+ exchange is seen in HEPES. Both Na(+)-independent Cl-/HCO3(-) exchange and V-type H(+)-ATPase mechanisms appear to be absent from these cells cultured in isotonic media.

Acid-Base Equilibrium↗
PubMed2001

The role of intracellular Ca buffers in determining the shape of the systolic Ca transient in cardiac ventricular myocytes.

We have studied the kinetics of decay of cardiac Ca transients elicited by either caffeine or electrical stimulation. The decay of the caffeine-evoked increase of intracellular Ca concentration ([Ca2+]i) could not be fit by a single exponential. A two exponential fit showed an initial rapid component. The rate of decay of total Ca was calculated from measured free Ca and the buffering properties of the cell. There was no initial rapid phase of decay of total Ca. We conclude that the rapid phase of decay of free Ca is due to a decrease of Ca buffering power at elevated [Ca2+]i. In contrast, the decay of the Ca transient, produced by voltage-clamp depolarization or field stimulation was fit by a single exponential. We suggest that these apparently simple kinetics arise because a tendency to saturation at elevated [Ca2+]i of the sarcoplasmic reticulum Ca-ATPase offsets the decrease of Ca buffering power. These data show the importance of Ca buffers as well as transporters in determining the kinetics of changes of [Ca2+]i.

Aniline Compounds↗