Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Christiansen-Douglas-Haldane effect describes the reduced CO2 binding capacity of oxygenated as compared to deoxygenated hemoglobin on the basis of its increased acidity. This study describes the development of the above effect during the first 2 min of hyperoxic intubation apnea. METHODS. After institutional approval 12 patients (NYHA III, ASA IV) scheduled for coronary-artery bypass grafting were studied after written informed consent. Routine monitoring measures included invasive arterial and pulmonary-arterial pressure monitoring. Pulse oximetry (Nellcor N 101) was also used during intubation apnea. Premedication consisted of flunitrazepam 2.0 mg p.o. the evening before operation and another 2.0 mg p.o. 90-120 min before induction of anesthesia. Following standardized preoxygenation induction of anesthesia was performed with 20-25 micrograms/kg fentanyl and 0.1 mg/kg pancuronium. After cessation of spontaneous respiration, controlled ventilation was continued with 100% oxygen until intubation. Thirteen arterial (a) and mixed-venous (v) blood samples were drawn sequentially immediately before and during the first 2 min of apnea and analyzed using Corning 150 pH/blood gas analyzer and a Corning 2500 CO-oximeter. RESULTS. As shown in Table 1 and Fig. 1, paO2 decreased from 485 +/- 100 mmHg before apnea to 376 +/- 68 mmHg after 2 min of apnea while pvO2 remained constant at 47-50 mmHg. Arterial oxygen saturation (saO2) showed stable values greater than 97% while svO2 slightly increased from 81.9% to 82.4% until the end of apnea. A biphasic increase was observed in paCO2 from 41.2 +/- 3.4 mmHg before to 54.5 +/- 3.9 mmHg at the end of apnea. An increase in pvO2 during apnea was linear from 45.7 +/- 3.9 mmHg to 51.9 +/- 4.0 mmHg. After 28.5 s of apnea paCO2 exceeded pvCO2 due to the Haldane effect ("pCO2 reversal"). During apnea, pHa decreased biphasically from 7.40 +/- 0.03 to 7.31 +/- 0.02. The speed of decrease was 0.106 pH units/min (5-35 s) in the 1st and 0.023 pH units/min in the 2nd min of apnea; pHv decreased almost linearly from 7.37 +/- 0.03 mmHg (5s) to 7.33 +/- 0.02 mmHg (115s). After 20.66 s of apnea pHa exceeded pHv ("pH reversal"); pH-reversal occurred earlier than pCO2 reversal (p less than = 0.05). CONCLUSIONS. During early hyperoxic apnea, venoarterial pH and pCO2 reversal can be observed due to the Christiansen-Douglas-Haldane effect. pH reversal starts earlier than pCO2 reversal. Reversal time is dependent on arterial-mixed-venous pCO2 difference (avDpCO2) before apnea, arterial-mixed-venous O2 saturation difference (avDsO2) and cardiac output. The amount of reversal is dependent on avDsO2, i.e. the pH difference of arterial and m
 ...
PMID:[The status of arterial and mixed venous blood gases in the initial phase of intubation apnea. Studies on the Christiansen-Douglas-Haldane effect]. 249 11

During an electron microscopical study of the localization of the nucleoside diphosphatase IDPase in Reissner's membrane of the inner ear, it was discovered that the distilled water in the knife trough produced an annoying artefact. It dissolved all the lead phosphate reaction product from the sections, and thus converted a positive phosphatase reactivity to a false negative one. The water in the knife trough had a pH of approximately 5.4. Calculations showed that this is an expected acidity, if CO2 in the air equilibrates with distilled water, and that there is 200,000 times more acid in the trough than necessary to dissolve all the reaction product from a ribbon of ultrathin sections. Experiments showed that the artefact could be avoided by adjusting the pH to neutrality with dilute ammonia.
 ...
PMID:Ultrathin sectioning for electron microscopy: the distilled water in the knife trough may extract phosphatase reaction products from the sections. 255 83

The one-electron reduction of 5-deazalumiflavin has been studied in aqueous solution in the acidity range H0 = -1 to pH 13 using the reducing species CO2-, e-aq and (CH3)2COH radicals. The spectral and other properties of the deazaflavin radicals formed were found to be independent of the reductant used. Four protolytic forms of the radical were distinguished with associated pKa values of 1.3 +/- 0.3, 6.0 +/- 0.3 and 10.7 +/- 0.3.
 ...
PMID:One-electron reduction of 5-deazalumiflavin in aqueous solution: a pulse radiolysis study. 256 66

In the turtle bladder it has recently been shown that CO2 stimulates H+ secretion, at least in part, by causing fusion of vesicles enriched in H+ pumps with the luminal plasma membrane. To test for the presence of this mechanism in the kidney we perfused collecting ducts and proximal straight tubules on the stage of an inverted epifluorescence microscope with fluorescein isothiocyanate dextran (70,000 mol wt) in CO2-free medium. After washout we noted punctate fluorescence in endocytic vesicles in some collecting ducts and in all proximal straight tubule cells. More cells took up fluorescent dextran in outer medullary than in cortical collecting ducts. Using the pH dependence of the excitation spectrum of fluorescein we found the pH of the vesicles to be acid (approximately pH 6). Addition of proton ionophores increased vesicular pH by 0.6 +/- 0.1 U, suggesting that the acidity of the vesicles was caused by H+ pumps. CO2 added to the medium (25 mmHg, pH 7.6 at 37 degrees C) reduced fluorescence intensity by 24 +/- 5% in cortical collecting ducts, 27 +/- 5% in medullary collecting ducts, and 25 +/- 5% in proximal straight tubules. Since this effect was prevented by the prior addition of colchicine to the bath, we believe that CO2 caused a decrease in cytoplasmic fluorescence by stimulating exocytotic fusion of the vesicles and thereby secretion of fluorescent dextran. This exocytotic fusion also occurred when tubules that were loaded with fluorescent dextran at a pCO2 of 37 mmHg were exposed isohydrically to a pCO2 of 114 mmHg; the mean decrease was 53 +/- 4%. We conclude that some cells in the collecting ducts and all cells in the proximal straight tubule incorporate fluorescent dextran into the apical cytoplasmic vesicles and acidify them with H+ pumps. CO2 causes fusion of these vesicles with the luminal membrane, but whether CO2 stimulates H+ secretion by increasing the number of functioning H+ pumps remains to be determined.
 ...
PMID:Carbon dioxide causes exocytosis of vesicles containing H+ pumps in isolated perfused proximal and collecting tubules. 258

This study systematically evaluates the effect of changes in the acid-base composition of the incubation media on the electrogenic H+ and HCO3- secretion (voltage clamp method and serosal ouabain) in the isolated turtle urinary bladder. Since the various cell types would change their acidity in a similar direction but to a variable degree, measured mean cell pH values (5,5-dimethyl-2,3-oxazolidinedione method) were used for an overall assessment of the changes in the acid-base status of the acid-transporting cells. Although addition of exogenous CO2 (0.7-3%) increased H+ secretion (JH+) 2- to 4-fold from a CO2-free control period, a further increase in the percent of CO2 did not enhance JH+ demonstrating a permissive but not a stimulatory role of CO2. Cyclic AMP plus 3-isobutyl-1-methylxanthine-induced electrogenic HCO3 secretion (JHCO3-) remained unaltered at 10% CO2 from a 5% CO2 control period. Cell acidosis resulting from either alterations in the PCO2/HCO3- levels or from NH4Cl in the bathing solution did not enhance JH+; by contrast maximal levels of acidification were found at cell pH values of about 7.40 and comparable effects on JH+ were found with a variety of PCO2/HCO3- combinations that led to a similar intracellular acidity.
 ...
PMID:Marginal effect of changes in acid-base status in vitro on rheogenic H+ and HCO3- secretion in turtle urinary bladder. 283 10

The effects of different insufflation media gases for pneumoperitoneum on the acidity of follicular fluid and blood acid--base balance were studied in two groups of patients during laparoscopic oocyte retrieval. Insufflation with 100% CO2 was compared with insufflation with 5% CO2 in air. End-tidal CO2 and the acid-base status of arterial blood, follicular and Douglas fluids were evaluated. When using 5% CO2 in air as insufflation gas, pH values and pCO2 levels observed in the aspirated follicular (pH: 7.35 +/- 0.06, pCO2: 38.8 +/- 4.5 mmHg) and Douglas fluid (pH: 7.40 +/- 0.07, pCO2: 38.5 +/- 6.2 mmHg) remained normal. With 100% CO2 insufflation, the follicular fluid pH (7.22 +/- 0.07) and pCO2 (53.1 +/- 10.9 mmHg) and the Douglas fluid pH (6.99 +/- 0.12) and pCO2 (90.3 +/- 18.4 mmHg) were grossly disturbed and outside the physiological range. No differences occurred in pO2 or HCO3 levels. These data suggest that pneumoperitoneum with 5% CO2 in air provides more optimal environmental conditions for oocytes used for in-vitro fertilization. However, further investigations on large patient groups are required to demonstrate whether such environmental conditions influence the success rate of in-vitro fertilization in humans.
 ...
PMID:Pneumoperitoneum induced pH changes in follicular and Douglas fluids during laparoscopic oocyte retrieval in humans. 285 15

Affinity labeling and comparative sequence analyses have placed Lys-166 of ribulosebisphosphate carboxylase/oxygenase from Rhodospirillum rubrum at the active site. The unusual nucleophilicity and acidity of the epsilon-amino group of Lys 166 (pKa = 7.9) suggest its involvement in catalysis, perhaps as the base that enolizes ribulosebisphosphate (Hartman, F.C., Milanez, S., and Lee, E.H. (1985) J. Biol. Chem. 260, 13968-13975). In attempts to clarify the role of Lys-166 of the carboxylase, we have used site-directed mutagenesis to replace this lysyl residue with glycine, alanine, serine, glutamine, arginine, cysteine, or histidine. All seven of these mutant proteins, purified by immunoaffinity chromatography, are severely deficient in carboxylase activity; the serine mutant, which is the most active, has a kcat only 0.2% that of the wild-type enzyme. Although low, the carboxylase activity displayed by some of the mutant proteins proves that Lys-166 is not required for substrate binding and argues that the detrimental effects brought about by amino acid substitutions at position 166 do not reflect gross conformational changes. As demonstrated by their ability to tightly bind a transition-state analogue (2-carboxyarabinitol 1,5-bisphosphate) in the presence of CO2 and Mg2+, some of the mutant proteins undergo the carbamylation reaction that is required for activation of the wild-type enzyme. Since Lys-166 is required neither for activation (i.e. carbamylation by CO2) nor for substrate binding, it must be essential to catalysis. When viewed within the context of previous related studies, the results of site-directed mutagenesis are entirely consistent with Lys-166 functioning as the base that initiates catalysis by abstracting the C-3 proton from ribulosebisphosphate. An alternative possibility that Lys-166 acts to stabilize a transition state in the reaction pathway cannot be rigorously excluded.
 ...
PMID:Function of Lys-166 of Rhodospirillum rubrum ribulosebisphosphate carboxylase/oxygenase as examined by site-directed mutagenesis. 310 87

The highlights of the literature and our work on tetany and hyperventilation are reviewed. Our studies concern the following: (1) the changes of [Ca2+] in circulating plasma caused by respiratory and "metabolic" acidosis and alkalosis; (2) critical plasma [Ca2+] levels associated with signs of tetany and neuromuscular blockade; (3) changes in cerebral [Ca2+]o caused by hypo- and hyper-calcaemia, and the changes in cerebral [Ca2+]o and pHo caused by acute systemic acidosis and alkalosis; and (4) effects of changing [Ca2+]o and pHo levels on synaptic transmission in hippocampal formation. Our main conclusions are (1) changes of plasma [Ca2+] caused by "metabolic" pH changes are greater than those associated with varying CO2 concentration; (2) acute systemic [Ca2+] changes are associated with small cerebral [Ca2+]o changes; (3) the decreases in systemic and cerebral [Ca2+]o caused by hyperventilation are too small to account for the signs and symptoms of hypocapnic tetany; (4) moderate decrease of [Ca2+]o depresses and its increase enhances synaptic transmission in hippocampal formation; and (5) H+ ions in extracellular fluid have a weak depressant effect on neuronal excitability. CO2 is a strong depressant, which is only partly explained by the acidity of its solution. CO2 concentration is a significant factor in controlling cerebral function.
 ...
PMID:Pathophysiology of pH and Ca2+ in bloodstream and brain. 311 5

When all peripheral chemoreceptors are denervated, animals continue to show increased ventilation when made to breathe CO2, indicating that receptors within the brain ("central chemoreceptors") are excited by acidity or changes in CO2. No cells have been identified within the brain that are indisputedly chemoreceptors for CO2 or H+, but there is abundant evidence that respiration can be affected by chemical, electrical, and thermal stimuli applied locally to the ventral surface of the medulla. Furthermore, the actions of traditional central chemical respiratory stimuli can be blunted or abolished after inhibition of neural function within this ventrolateral medullary shell (VMS). The VMS is an integrative region for cardiovascular and respiratory function and may be involved in nociception. The distinction between the former two is not always clear, but recent studies using microinjection techniques seem promising for identifying the respiratory substrates. The many recent advances elucidating anatomic connections between the VMS and other brain regions are important but do not directly address the question of the site of central respiratory chemosensitivity. Knowledge of such connections, however, should provide more definitive opportunities for addressing this question.
 ...
PMID:Central chemoreceptors. 354 73

Eleven-kilogram parcels of 2-row and 6-row barley initially at 18% moisture content were implanted in dry bulk oats in a farm granary in Manitoba for 60 weeks between August 1983 and October 1984. Temperature, moisture content, O2 and CO2 levels, fat acidity values, seed germination, microfloral incidence and abundance and the presence of major mycotoxins (aflatoxins, sterigmatocystin, ochratoxin A, citrinin, penicillinic acid, patulin) were monitored. Ochratoxin A reached maximum levels of 0.97 ppm by week 24 in the 6-row barley, and 0.05 ppm by week 28 in the 2-row; no other mycotoxins were detected. The effect of cultivar type was significant (P less than 0.01) with greater effects in the 6-row barley for the following parameters: fat acidity value, germination, incidence of Alternaria alternata, Penicillium spp. and Helminthosporium sativum, total fungal propagule count and ochratoxin A levels. The effect of time was significant (P less than 0.05) for all variables except oxygen, carbon dioxide, Aspergillus versicolor, and total fungal propagule count. The interaction between cultivar and time was significant (P less than 0.01) for Alternaria and Helminthosporium only.
 ...
PMID:Mycotoxin formation in moist 2-row and 6-row barley during granary storage. 357 39


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>