Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Bicarbonates”

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 631 records · Page 35Linked to original sources
PubMed1997

Bicarbonate may Be required for ligation of manganese in the oxygen-evolving complex of photosystem II.

It was previously shown in the photosystem II membrane preparation DT-20 that photoxidation of the oxygen-evolving manganese cluster was blocked by 0.1 mM formate, unless 0.2 mM bicarbonate was present as well [Wincencjusz, H., Allakhverdiev, S. I., Klimov, V. V., and Van Gorkom, H. J. (1996) Biochim. Biophys. Acta 1273, 1-3]. Here it is shown by measurements of EPR signal II that oxidation of the secondary electron donor, YZ, is not inhibited. However, the reduction of is greatly slowed and occurs largely by back reaction with reduced acceptors. Bicarbonate is shown to prevent the loss of fast electron donation to . The release of about one or two free Mn2+ per photosystem II during formate treatment, and the fact that these effects are mimicked by Mn-depletion, suggests that formate may act by replacing a bicarbonate which is essential for Mn binding. Irreversible light-induced rebinding in an EPR-silent form of Mn2+ that was added to Mn-depleted DT-20 was indeed found to depend on the presence of bicarbonate, as did the reconstitution in such material of both the fast electron donation to and the UV absorbance changes characteristic of a functional oxygen-evolving complex. It is concluded that bicarbonate may be an essential ligand of the functional Mn cluster.

Bicarbonates↗
PubMed2001

Bicarbonate as a proton donor in catalysis by Zn(II)- and Co(II)-containing carbonic anhydrases.

Catalysis of (18)O exchange between CO(2) and water catalyzed by a Co(II)-substituted mutant of human carbonic anhydrase II is analyzed to show the rate of release of H(2)(18)O from the active site. This rate, measured by mass spectrometry, is dependent on proton transfer to the metal-bound (18)O-labeled hydroxide, and was observed in a site-specific mutant of carbonic anhydrase II in which a prominent proton shuttle residue His64 was replaced by alanine, which does not support proton transport. Upon increasing the concentration of bicarbonate, the rate of release of H(2)(18)O increased in a saturable manner to a maximum of 4 x 10(5) s(-)(1), consistent with proton transfer from bicarbonate to the Co(II)-bound hydroxide. The same mutant of carbonic anhydrase containing Zn(II) had the rate of release of H(2)(18)O smaller by 10-fold, but rate of interconversion of CO(2) and HCO(3)(-) about the same as the Co(II)-containing enzyme. These data as well as solvent hydrogen isotope effects suggest that the bicarbonate transferring the proton is bound to the cobalt in the enzyme. The enhancement of (18)O exchange caused by increasing bicarbonate concentration during catalysis by the Zn(II)-containing carbonic anhydrase from the archaeon Methanosarcina thermophila suggests that a very similar mechanism for proton donation by bicarbonate occurs with this wild-type enzyme.

Amino Acid Substitution↗
PubMed2005

The activity of Escherichia coli cyclopropane fatty acid synthase depends on the presence of bicarbonate.

Cyclopropane fatty acid (CFA) synthases catalyze the formation of cyclopropane rings on isolated and unactivated olefinic bonds within various fatty acids; the methylene carbon is derived from the activated methyl group of (S)-adenosylmethionine. The E. coli enzyme is the prototype for this class of enzymes, which include the cyclopropane mycolic acid (CMA) synthases, which are potential targets for the design of antituberculosis agents. Crystal structures of several CMA synthases have recently been solved, and electron density attributed to a bicarbonate ion was found in or near the active site. Because a functional assay for CMA synthases has not been developed, the relevance of the bicarbonate ion has not been established. CFA synthase is 30-35% identical to the CMA synthases that have been analyzed structurally, suggesting that the mechanisms of these enzymes are conserved. In this work, we show that indeed the activity of CFA synthase requires bicarbonate, and that it is inhibited by borate, a planar trigonal molecule that mimics the structure of bicarbonate. We also show that substitutions of the conserved amino acids that act as ligands to the bicarbonate ion based on the structure of CMA synthases result in drastic losses in the activity of the protein.

Bicarbonates↗
PubMed2003

Sensory and physical properties of peanut brittle prepared in different types of cookware and with different levels of sodium bicarbonate.

Two studies to evaluate peanut brittle containing either raw or roasted peanuts were conducted. In the first study, brittles were prepared in iron, aluminum, stainless steel and nonstick stainless steel pans. In the second study, brittles containing 0, 2 or 4 g of sodium bicarbonate prepared in either stainless steel or nonstick stainless steel pans were evaluated. All brittles were evaluated for color, shear strength and sensory properties at 0, 30 and 60 days. Products prepared in a nonstick stainless steel pan and those with added sodium bicarbonate were lighter, more yellow and slightly greener than other products. Pan type did not affect shear force but increasing sodium bicarbonate was associated with decreasing force needed to shear brittles. Peanut and caramel aromas were not affected by pan type or sodium bicarbonate level but were greater (p < 0.05) in products containing roasted peanuts. Burned flavors were more prevalent in products prepared in iron or stainless steel pans with roasted peanuts. More intense sweet and buttery flavors were detected as level of sodium bicarbonate increased.

Arachis↗
PubMed1979

A redefinition of normal acid-base equilibrium in man: carbon dioxide tension as a key determinant of normal plasma bicarbonate concentration.

It has been shown recently that normal acid-base equilibrium in the dog is characterized by a strong positive correlation between plasma bicarbonate concentration and PCO2. The present study was undertaken to examine the possibility that a similar relationship between normal levels of PCO2 and plasma bicarbonate might be present in man. The results indicate that values for bicarbonate within the normal range are highly dependent upon the prevailing level of PCO2 ([HCO3-] = 0.36 PaVCO2 + 10.4; r = 0.73). Thus, approximately 50% of the normal variance in bicarbonate concentration is explained simply by the variance in PCO2. The joint confidence region for bicarbonate concentration and PCO2, that can be derived from these data provides a new and more rigorous definition of normal acid-base equilibrium in man.

Acid-Base Equilibrium↗
PubMed1982

Acetate and bicarbonate fluctuations and acetate intolerance during dialysis.

Plasma bicarbonate losses during acetate dialysis were prevented by using a combination of acetate and bicarbonate in the dialysate. In 21 patients who were treated with combination dialysate, the fall in mean blood pressure (MBP), and frequency of symptoms, and post-dialysis task performance were all similar to that observed during dialysis with acetate alone. Furthermore, dialysis performed with bicarbonate dialysate resulted in significantly smaller MBP drops, fewer symptoms, and an improved task performance compared to either an acetate or a combination dialysis. These findings indicate that the presence of acetate, rather than a bicarbonate loss, was responsible for the patients' intolerance to acetate dialysis. Patients symptomatic on acetate dialysis had a similar ultrafiltration rate, weight loss, MBP drops, and postdialysis serum acetate levels; they were similar in age and weight to symptom-free patients. Thus, the toxic effect of acetate was not related to serum acetate level. There was no difference in bicarbonate dialysis between patients with symptoms on acetate and the symptom-free patients in reference to MBP drops and task performance. This finding suggests that symptomatic patients were not simply less tolerant to the process of dialysis, but differed from symptom-free patients in their response to the presence of acetate.

Acetates↗
PubMed1985

Comparative effects of acetate and bicarbonate hemodialysis on left ventricular function.

To assess the comparative effects of hemodialysis with acetate versus bicarbonate base on left ventricular systolic function, we performed M-mode echocardiography on 36 patients prior to and immediately following 4-hr maintenance hemodialysis. Patients were initially dialyzed against either sodium acetate or sodium bicarbonate and 1 week later were dialyzed against the alternate base. The mean velocity of circumferential fiber shortening (mean Vcf, circumferences/s) was used to assess left ventricular systolic function. In patients with normal pre-dialysis mean Vcf hemodialysis with acetate produced no significant change in mean Vcf, whereas hemodialysis with bicarbonate produced a significant increase in mean Vcf. In patients with low pre-dialysis mean Vcf hemodialysis with either base produced a significant increase in mean Vcf. Mean Vcf values obtained after hemodialysis with bicarbonate were significantly higher than those obtained after hemodialysis with acetate, both in patients with normal and low pre-hemodialysis mean Vcf. We conclude that hemodialysis with bicarbonate produces a comparatively greater improvement in left ventricular systolic function than hemodialysis with acetate.

Acetates↗
PubMed1992

Effect of prolonged bicarbonate administration on plasma potassium in terminal renal failure.

In hemodialysis patients with hyperkalemia, i.v. sodium bicarbonate has recently been found to be ineffective in lowering plasma potassium within one hour. In the present study the effect of a prolonged bicarbonate infusion on plasma potassium was investigated. Twelve patients with terminal renal failure who were on hemodialysis were infused i.v. with 8.4% sodium bicarbonate (4 mmol/min) for one hour and with 1.4% (0.5 mmol/min) for five hours (total amount 390 mmol). Plasma bicarbonate rose from 17.5 at baseline to 28.4 and 29.6 mmol/liter, and blood pH from 7.32 to 7.46 and 7.48 at one and six hours, respectively. Plasma potassium did not change significantly after one and two hours (6.04 at baseline, 5.91 and 5.77 mmol/liter, respectively). Only at four and six hours did a moderate decline to 5.44 (P less than 0.05) and to 5.30 (P less than 0.01) occur, of which approximately half was calculated to be due to ECF volume expansion. However, no change or a very moderate decrease was observed in three patients even after six hours (+0.19, -0.32, -0.33 mmol/liter). Five patients with higher baseline plasma potassium (6.15 to 8.15 mmol/liter) behaved like seven with lower levels (5.25 to 5.87 mmol/liter). Tented T-waves in the ECG of seven patients disappeared after one hour only in one patient. Plasma aldosterone, norepinephrine and epinephrine were normal to elevated before and tended to fall during i.v. bicarbonate. Plasma dopamine and insulin were in the normal range.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2003

Involvement of CFTR in uterine bicarbonate secretion and the fertilizing capacity of sperm.

Cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-activated chloride channel expressed in a wide variety of epithelial cells, mutations of which are responsible for the hallmark defective chloride secretion observed in cystic fibrosis (CF). Although CFTR has been implicated in bicarbonate secretion, its ability to directly mediate bicarbonate secretion of any physiological significance has not been shown. We demonstrate here that endometrial epithelial cells possess a CFTR-mediated bicarbonate transport mechanism. Co-culture of sperm with endometrial cells treated with antisense oligonucleotide against CFTR, or with bicarbonate secretion-defective CF epithelial cells, resulted in lower sperm capacitation and egg-fertilizing ability. These results are consistent with a critical role of CFTR in controlling uterine bicarbonate secretion and the fertilizing capacity of sperm, providing a link between defective CFTR and lower female fertility in CF.

Animals↗
PubMed1996

Total energy expenditure and physical activity measured with the bicarbonate-urea method in patients with human immunodeficiency virus infection.

1. Our objectives were to measure total energy expenditure, the daily variation in total energy expenditure and the physical activity level in a group of HIV-positive subjects using the bicarbonate-urea method. The study also aimed to asses the practicalities of using the bicarbonate-urea technique in free-living conditions. 2. Total energy expenditure was measured with the bicarbonate-urea method over 2 consecutive days (1 day in one subject) in 10 male patients with HIV infection (median CD4 count = 30). Resting energy expenditure was measured by indirect calorimetry. Physical activity level (total energy expenditure/resting energy expenditure) was calculated from these measurements and from activity diaries. 3. Resting energy expenditure was found to be 7.46 +/- 0.87 MJ/day, 5% higher than predicted values. Total energy expenditure was 10.69 +/- 1.95 MJ/day with an intra-individual day-to-day variation of 6 +/- 6%. The measured physical activity level was 1.42 +/- 0.14, higher than the diary estimate of 1.34 +/- 0.16 (P = 0.029), and there were large intermethod differences in individual values. The subcutaneous infusion of bicarbonate was well tolerated and did not seem to restrict normal activities. 4. Total energy expenditure was not elevated in the group of HIV-positive subjects when compared with reference values for normal subjects. The physical activity level of the patients in this study was lower than that measured using other techniques in healthy young men, but was compatible with that expected for people leading a sedentary lifestyle. Reductions in physical activity in patients with HIV are likely to contribute to the wasting process and physical activity level may thus be a clinically useful measure. This study has also provided the first tracer estimate of the day-to-day variation in total energy expenditure. The bicarbonate-urea method represents an important new investigative tool for measuring total energy expenditure which has previously only been possible within the confines of a whole-body calorimeter or using the expensive doubly labelled water method.

Adult↗
PubMed1996

Recovery of 13CO2 and 14CO2 in human bicarbonate studies: a critical review with original data.

1. In order to establish biological and/or methodological explanations for the wide variability in recovery (50-100%) of labelled CO2 after administration of [13C]bicarbonate or [14C]bicarbonate, 34 human bicarbonate studies involving 480 subjects were analysed, and potential methodological issues were investigated in the laboratory. 2. Overall, continuous infusion studies reported a higher recovery than bolus studies (84 +/- 11% versus 69 +/- 12%; P < 0.001). No significant differences in recovery were found between 14C and 13C studies, children and adults, obese and lean subjects, or rest and exercise (steady state). Higher recoveries were found during feeding than during fasting (84 +/- 8% versus 74 +/- 7%; P < 0.001). Different methods used to analyse the results (0-10%) and different study protocols, which include differences in the duration of infusions and background drift in 13C enrichment (0-10%), contribute to the variability. 3. The laboratory studies suggest multiple sources of potential error, including loss of CO2 from the scintillation fluid (up to > 30%, but only in 14C studies in which the scintillation fluid is not alkalized), diffusion of CO2 through syringes and tubing (0 to > 10%), non-linearity of CO2 analysers (up to 8%), inaccuracies in the measurement of bicarbonate concentrations (13C studies) or the strength of CO2-trapping agents (14C studies; 0-8%). 4. It is concluded that much of the variability in the recovery of labelled bicarbonate is likely to be attributable to methodological differences, and that attention to these will ensure better interpretation of metabolic studies that involve oxidation of carbon-labelled substrates.

Adult↗
PubMed1998

Acid-induced duodenal mucosal nitric oxide output parallels bicarbonate secretion in the anaesthetized pig.

We recently showed the involvement of the L-arginine/nitric oxide (NO) pathway in acid-induced duodenal mucosal bicarbonate secretion in rats. The aim of the present study was to confirm this observation in pigs by direct measurements of NO production. Experiments were performed on 16 anaesthetized pigs of both sexes treated with guanethidine (6 mg kg-1, intravenously). A duodenal segment, devoid of pancreaticobiliary influxes, was perfused with saline and the duodenal mucosal bicarbonate secretion was calculated from continuous measurements of pH and PCO2. The perfusate contents of NO and its oxidative product nitrite were determined by chemiluminescence, after reduction of nitrite to NO. Luminal acidification with 30 mM hydrochloric acid increased the output of bicarbonate as well as NO to the perfusate, by 195 +/- 45% and 106 +/- 10%, respectively. These responses to acid were markedly inhibited by adding the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 0.3 mM) to the perfusate. The inhibitory effect of L-NMMA could be reversed by administration of L-arginine (3 mM). The study presents simultaneous measurements of bicarbonate and NO outputs to a duodenal luminal perfusate. The results strongly support the view that the L-arginine/NO pathway is involved in the acid-induced duodenal mucosal bicarbonate secretory response.

Anesthetics, Combined↗
PubMed2003

Effects of bicarbonate buffered dialysate on human peritoneal mesothelial cell intracellular calcium homeostasis.

This study compares the biocompatibility of two bicarbonate-based peritoneal dialysis (PD) solutions using the measurement of intracellular free calcium (Ca(i)2+)) as a sensitive parameter of cell function in human peritoneal mesothelial cells (hPMC). Fura-2-loaded hPMC suspensions were exposed to bicarbonate (38 mmol/L) and bicarbonate (25 mmol/L), lactate-buffered PD (15 mmol/L) solutions at pH 7.4 and compared with Krebs-Ringer physiological saline (KRS; pH = 7.4). Resting Ca(i)2+ values and 4br-A23187 (1.0 micro mol/L) induced transients were compared in treatment and control groups. In separate studies, the effect that low saline pH had on Ca(i)(2+) homeostasis was examined. Suspended cells or cells attached to coverslips were bathed in citric acid-phosphate (McIllvaine's) buffered saline (MBS, pH = 7.4). Cells were acidified (pH = 5.3) with citric acid and then challenged with ionophore. Ionophore challenge produced a significantly reduced Ca(i)2+ transient response in cells exposed to the bicarbonate/lactate fluid compared with bicarbonate or KRS. Acidified cell suspensions produced a small monophasic Ca(i)2+ transient rise that was short lived. Gradual recovery of MBS to pH 7.4 produced no changes to Ca(i)2+ homeostasis of cell monolayers. Ionophore treatment produced a biphasic response identical to cells bathed in KRS. This study has demonstrated that short-term exposure to bicarbonate did not alter Ca(i)2+ homeostasis directly, or subsequent modulation of intracellular pH. The MBS system provided a reliable method of modifying the external pH during continuous Ca(i)2+ measurement.

Bicarbonates↗
PubMed1989

Regulation of duodenal bicarbonate secretion during stress by corticotropin-releasing factor and beta-endorphin.

Proximal duodenal mucosal bicarbonate secretion is an important factor in the pathogenesis of duodenal ulcer disease. To examine the central nervous system regulation of duodenal bicarbonate secretion, an animal model was developed that allowed cerebroventricular and intravenous injections as well as collection of duodenal perfusates in awake, freely moving rats. The hypothalamic peptide corticotropin-releasing factor (CRF) and stress (physical restraint) significantly stimulated duodenal bicarbonate secretion. These responses were abolished by pretreatment of the animals with the CRF receptor antagonist alpha-helical CRF-(9-41), hypophysectomy, and naloxone. In contrast, blockade of autonomic efferents by surgical and pharmacological means did not prevent the stimulatory effects of stress and CRF. Intravenous, but not cerebroventricular, administration of beta-endorphin that produced plasma concentrations of beta-endorphin that were similar to those produced by exogenous CRF and stress significantly stimulated duodenal bicarbonate secretion. These results indicate that endogenous CRF released during stress and exogenously administered CRF stimulate duodenal bicarbonate secretion by release of beta-endorphin from the pituitary, thus, demonstrating a functional hypothalamus-pituitary-gut axis.

Adrenalectomy↗
PubMed2005

Effect of chilling, polyphosphate and bicarbonate on quality characteristics of broiler breast meat.

1. An experiment was conducted to assess the effect of tetrasodium pyrophosphate and sodium bicarbonate on colour and sensory attributes of pre- and post-chilled breast meat. 2. Three groups of 6 halves of breasts (pre-chill) immediately after slaughter were treated with 3% tetrasodium pyrophosphate, 3% sodium bicarbonate in 2% NaCl or 2% NaCl alone (control); the remaining 6 halves (post-chill) were stored overnight at 4 degrees C and then treated similarly. Both the pre- and post-chill samples were held at 4 degrees C for 24 h and pH, water holding capacity, cooking loss, CIE colour values and sensory attributes were recorded. 3. Chilling had few effects on the meat characteristics measured in this study. 4. Treatment with phosphate and bicarbonate increased pH in both the pre- and post-chill groups. Treated breasts exhibited lower L* and higher a* value (more red) than controls. 5. A sensory evaluation study revealed improvements in colour and other sensory attributes of cooked broiler breast meat in all treated samples compared to the control. 6. The findings suggest that tetrasodium pyrophosphate and sodium bicarbonate, when injected post mortem, will have beneficial effects on several physico-chemical (pH, colour, WHC %, cooking loss) and sensory attributes of broiler meat. However, phosphate had a smaller effect than bicarbonate.

Animals↗
PubMed2003

Vitamin C (ascorbic acid) induced hydroxyl radical formation in copper contaminated household drinking water: role of bicarbonate concentration.

We have previously shown that Vitamin C (ascorbic acid) can trigger hydroxyl radical formation in copper contaminated household drinking water. We report here that the capacity of ascorbic acid to catalyze hydroxyl radical generation in the drinking water samples is strongly dependent on the bicarbonate concentration (buffer capacity and pH) of the samples. We found that at least 50 mg/l bicarbonate was required in the water samples to maintain the pH over 5.0 after ascorbic acid addition. At this pH, that is higher than the pKa1 4.25 of ascorbic acid, a hydroxyl radical generating redox cycling reaction involving the mono-anion of vitamin C and copper could take place. The ascorbic acid induced hydroxyl radical generating reaction could easily be mimicked in Milli-Q water by supplementing the water with copper and bicarbonate. Our results demonstrate that ascorbic acid can induce a pH dependent hydroxyl radical generating reaction in copper contaminated household tap water that is buffered with bicarbonate. The impact of consuming ascorbic acid together with copper and bicarbonate containing drinking water on human health is discussed.

Anions↗
PubMed2004

Effect of lactate and bicarbonate on human peritoneal mesothelial cells, fibroblasts and vascular endothelial cells, and the role of basic fibroblast growth factor.

BACKGROUND: In patients on long-term continuous ambulatory peritoneal dialysis (CAPD), peritoneal dysfunction may occur due to loss of peritoneal mesothelial cells, peritoneal fibrosis and neovascularization. Lactate, long used as a buffer in peritoneal dialysates, has been substituted by bicarbonate in recent years. However, their effects on the peritoneum of CAPD patients are unknown. This study investigated the influence of lactate and bicarbonate on peritoneal dysfunction in CAPD patients. METHODS: The mitochondrial activity of human peritoneal mesothelial cells (HPMCs) and their expression of basic fibroblast growth factor (bFGF) were studied after culture under various conditions. We also assessed the mitochondrial-activating effect of the supernatant of those cultures on human peritoneal fibroblasts (HPFBs) and human umbilical vein endothelial cells (HUVECs) and the effect of recombinant human bFGF on the mitochondrial activity of HPFBs and HUVECs. We used the WST-1 assay to determine mitochondrial activity in HPMC. RESULTS: At pH 7.4, the mitochondrial activity of HPMCs was lowest in a medium containing 40 mM (Lac), intermediate in a lactate (15 mM) plus bicarbonate (25 mM) medium (Lac/Bic), and highest in a 40 mM bicarbonate medium (Bic). In culture supernatant, the increase of bFGF was: Lac > Lac/Bic > Bic. Mitochondrial activation of HPFBs and HUVECs was stimulated by HPMC culture supernatants in the following decreasing order: Lac > Lac/Bic > Bic. The effects of these supernatants were suppressed by a bFGF-neutralizing antibody, while recombinant bFGF caused concentration-dependent mitochondrial activation in HPFBs and HUVECs. CONCLUSIONS: The role of bFGF in peritoneal fibrosis and neovascularization may be important. A bicarbonate-containing medium is better than a lactate-containing medium for preserving cell viability in HPMCs and preventing bFGF expression by these cells.

Bicarbonates↗
PubMed2003

Caspase-independent exposure of aminophospholipids and tyrosine phosphorylation in bicarbonate responsive human sperm cells.

Only capacitated sperm cells are able to fertilize egg cells, and this process is triggered by high levels of bicarbonate. Bicarbonate renders the plasma membrane more fluid, which is caused by protein kinase A (PKA)-mediated alterations in the phospholipid (PL) bilayer. We studied exposure of phosphatidylserine (PS) and phosphatidylethanolamine (PE) in human sperm cells. Surface exposure of PS and PE on sperm cell activation in vitro was found to be bicarbonate dependent and restricted to the apical area of the head plasma membrane. The PL scrambling in bicarbonate-triggered human sperm was not related to apoptosis, because the incubated cells did not show any signs of caspases or degeneration of mitochondria or DNA. The PL scramblase (PLSCR) gene family has been implicated in this nonspecific, bidirectional PL movement. A 25-kDa isoform of PLSCR was identified that was homogeneously distributed in human sperm cells. We propose that compartment-dependent activation of PKA is required for the surface exposure of aminophospholipids at the apical plasma membrane of sperm cells. Bicarbonate-induced PL scrambling appears to be an important event in the capacitation process, because the entire intact scrambling sperm subpopulation showed extensive tyrosine phosphorylation, which was absent in the nonscrambling subpopulation. The proportion of live cells with PL scrambling corresponded with that showing capacitation-specific chlortetracyclin staining.

Acrosome Reaction↗