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PubMed2002

Evaluation and therapeutic regulation of erectile dysfunction with visual stimulation test. An objective approach by using sildenafil citrate test.

AIM: An objective evaluation of the psychogenic cause of erectile dysfunction by performing the visual stimulation tumescence and rigidity (VSTR) test and sildenafil citrate test, together with the effectiveness of sildenafil citrate medication on impotence caused by different etiologies. MATERIAL AND METHODS: Between 1998 and 2000, a total of 36 men (12 patients with diabetic etiology, 5 patients with vasculogenic risk factor) were enrolled in this study. The mean age of patients was 53 (27-67) years. Following standard questionnaires, including a detailed anamnesis from an andrologic viewpoint, VST was performed in an ambulatory setting and beginning with a test dose of 50 mg. At the end of 2 h, the data was evaluated with computer assistance (Rigiscan device) and if a satisfactory erection had not occurred, an additional second dose of sildenafil citrate (50 mg) was given until there was a satisfactory erection. Results obtained from VST: results were classified as group I (fully rigidity, >10 min erection, >70% of rigidity, possible vaginal penetration), group II (unstable erection, 5 min erection, >70% of rigidity, possible vaginal penetration) and group III (tumescence without rigidity, <5 min erection, <70% of rigidity, impossible vaginal penetration). The results obtained during the first 1 h of the VSTR test were regarded as the patient's own erectile condition and later data was accepted as the real effect of sildenafil citrate. The Fisher exact test was used for statistical evaluation including pre- and post-sildenafil effect on erectile rigidity and duration of erection. RESULTS: The erection status of patients was sufficient in 17 (47.2%) in group I, it was insufficient but sufficient enough with an increased dose of sildenafil citrate in 10 (27.7%) in group II, and insufficient without/with full dose of sildenafil citrate in 9 (25%) in group III. Considering rigidity and total erectile period, there was a statistical significant difference between the first two groups with respect to the early and late sildenafil citrate effects on the VSTR test (p < 0.05). Again, 10 patients with known risk factors (diabetes mellitus 5 and vasculogenic 5) in the second group seemed to give a good response to repeated dosage of sildenafil citrate which has been found to be very interesting. However, the rest of the diabetic patients (n = 7) in the third group showed no erection despite the increasing and repeated doses of sildenafil citrate. CONCLUSION: Sildenafil citrate with the VSTR test has effective and reliable results which was regarded as very important to diagnose and determine objectively the amount of therapeutic doses in impotence. In accordance with the literature data, our results also confirm the reliability and the practical nature of the VSTR test, which is less time-consuming and cheaper than the nocturnal penile tumescence and rigidity (NPTR) test. In the VSTR test, necessary doses of medication needed for satisfactory erection were easily regulated in patients with certain kinds of impotence. Additionally, self-criticism advantage of the patients on erection and an unnecessary need for regular sexual partners may make this test preferable in the near future. However, we believe that a large group of patients with other definite parameters are certainly needed in order to obtain more reliable data.

Adult↗
PubMed2000

Effects of sildenafil citrate (Viagra) combined with nitrate on the heart.

BACKGROUND: Sildenafil citrate (Viagra) is indicated for the treatment of erectile dysfunction. Large and sudden decreases in systemic blood pressure were reported in a substantial number of patients taking sildenafil citrate combined with nitroglycerin. We studied the effect of sildenafil citrate on the relationship between changes in systemic blood pressure and coronary blood flow. METHODS AND RESULTS: Healthy male beagles were used to assess systemic blood pressure, pulmonary arterial pressure, and flow in the left circumflex artery (in which a critical stenosis was established) and left anterior descending coronary artery. After measurement of the hemodynamic variables, 2 mg/kg sildenafil citrate was administered via a nasogastric tube. Hemodynamic changes were monitored for 1 hour. Subsequently, the acute effect of nitrate combined with sildenafil citrate was studied by the bolus injection of 0.2 mg isosorbide dinitrate before and after sildenafil citrate. Systemic blood and pulmonary arterial pressures and circumflex flow did not change during this study; however, left anterior descending coronary arterial flow increased from 16.0+/-5.8 to 24.6+/-8.7 mL/min 1 hour after administration of sildenafil citrate. The prolongation of systemic blood pressure decrease and the circumflex flow decrement induced by isosorbide dinitrate after sildenafil citrate were significantly larger and longer than those before sildenafil citrate. CONCLUSIONS: Sildenafil citrate had the effect of vasodilation in a normal coronary artery; however, a combined effect with nitrate resulted in large and protracted decreases in systemic blood pressure and coronary blood flow in vessels with critical stenosis.

Administration, Oral↗
PubMed2005

[Influence of urinary citrate levels on spontaneous calcium oxalate dihydrate crystalluria].

INTRODUCTION: Calcium oxalate is the leading cause of renal stones and is mainly due to hypercalciuria, hyperoxaluria and/or hypocitraturia. Citrate is considered to be an effective inhibitor of calcium oxalate crystallization and is therefore increasingly prescribed as maintenance therapy for patients with calcium stones, but no study has investigated the effect of urinary citrate levels on spontaneous calcium oxalate crystalluria in human urine. In this study, the authors examined the relationships between the calcium oxalate molar product, the urinary citrate concentration and weddellite (oxalate calcium dihydrate) crystalluria, the most frequent crystalline form of calcium oxalate in human urine. MATERIAL AND METHODS: Crystalluria analysis and calcium, oxalate and citrate assays were performed on a series of 10,222 first morning urine samples from 4,809 stone patients and 453 first morning urine samples from 317 control subjects. The frequency and characteristics of weddellite crystalluria were determined as a function of the calcium oxalate molar product (pCaOx) and urinary citrate concentration. RESULTS: 1,940 urine samples (18.2%) presented weddellite crystalluria, which was pure in 1,378 urine samples from stone patients (13.5%) and 43 urine samples (9.5%) from controls (p < 0.05). The crystalluria rate in stone patients ranged from 4% for pCaOx < 1 (mmol/l)2 to 81.3% for pCaOx > or = 3 (mmol/l)2 (p < 0.0001). Over the same interval of pCaOx, weddellite crystalluria ranged from 1.5% to 72.2% in control subjects. An increase of urinary citrate excretion from 0.5 to 5 mmol/l significantly lowered the frequency of crystalluria from 32.4% to 10.1% for a pCaOx between 1 and 2 (mmol/l)2 (p < 0.0001) and from 63% to 27.9% for a pCaOx between 2 and 3 (mmol/l)2 (p < 0.001). For pCaOx values > or = 3 (mmol/l)2, urinary citrate excretion no longer significantly influenced the frequency of crystalluria. The number of crystals and aggregates and the maximum dimensions of aggregates were only influenced by the urinary citrate concentration when the pCaOx product was < 2 (mmol/l)2. CONCLUSION: The main determinant of the frequency and characteristics of weddellite crystalluria is the pCaOx molar product. The beneficial effect of the urinary citrate concentration on the frequency of crystalluria is observed for pCaOx values < 3 (mmol/l)2, but only for pCaOx values < 2 (mmol/l)2 for the characteristics of crystalluria such as the number and dimensions of crystals and aggregates. This means that therapeutic measures designed to increase urinary citrate concentrations can only be effective when pCaOx has been previously lowered by increased diuresis or specific reduction of urinary calcium and/or urinary oxalate levels.

Calcium↗
PubMed1977

Interactions of citrate synthases from osmoconforming and osmoregulating animals with salt: possible signs of molecular eco-adaptation?

This study considers differential sensitivity of citrate synthase (citrate oxaloacetatelyase [CoA acetylating]) EC 4.1.3.7. from an osmoconforming animal (sea anemone) and an osmoregulating animal (the pig) to salt. Attention is drawn to the fact that the osmoconforming sea anemone is in essence a sessile creature while the pig is readily mobile and able to change its ionic environment at will. It had been shown earlier that citrate synthase from another osmoconformer (oyster) is also not sensitive to ionic strength while citrate synthase from osmoregulating white shrimp is sensitive to increasing levels of salt. However, these enzymes are characteristically regulated by ATP and alpha-ketoglutarate. Both forms of citrate synthase are denatured by 6 M guanidine hydrochloride and are aided by salt levels in their refolding but the rate and extent of refolding of the osmoconformer citrate synthase are greater than those of the osmoregulator citrate synthase. Catalytic activity of both forms of citrate synthase is inhibited by incubation in distilled water; osmoconformer citrate synthase was inhibited completely in 7 h while osmoregulator citrate synthase was inhibited only 60% in this time and 80% after 22 h in distilled water. The eco-adaptive and evolutionary implications of these findings are discussed.

Adaptation, Physiological↗
PubMed1994

Citrate and renal calculi: an update.

Citrate is an inhibitor of the crystallization of stone-forming calcium salts. Hypocitraturia, frequently encountered in patients with nephrolithiasis, is therefore an important risk factor for stone formation. Potassium citrate provides physiological and physicochemical correction and inhibits new stone formation, not only in hypocitraturic calcium nephrolithiasis but also in uric acid nephrolithiasis. Inhibition of stone recurrence has now been validated by a randomized trial. Ongoing research has disclosed additional causes of hypocitraturia (sodium excess, low intestinal alkali absorption, but not primary citrate malabsorption). Moreover, new insights on potassium citrate action have been shown, notably that some of absorbed citrate escapes oxidation and contributes to the citraturic response, that ingestion with a meal does not sacrifice physiological or physicochemical action, that orange juice mimics but does not completely duplicate its actions, that potassium citrate may have a beneficial bone-sparing effect, that it may reduce stone fragments following ESWL, and that danger of aluminum toxicity is not great in subjects with functioning kidneys. Finally, the research on potassium citrate has led to two promising products, calcium citrate as an optimum calcium supplement and potassium-magnesium citrate which may be superior to potassium citrate in the management of stone disease.

Citrates↗
PubMed2001

Multiple compartments with different metabolic characteristics are involved in biosynthesis of intracellular and released glutamine and citrate in astrocytes.

The metabolism of glucose and lactate was investigated in cultured mouse cerebellar astrocytes, a culture preparation consisting of a homogeneous population of cells, by incubating the cells in a medium containing either [U-(13)C]glucose or [U-(13)C]lactate in combination with unlabeled lactate and glucose, respectively. After the incubation, cell extracts and media were analyzed by GC/MS (gas chromatography/mass spectrometry) for labeling patterns in aspartate, glutamate, and glutamine, as well as the tricarboxylic acid (TCA) cycle constituents citrate and fumarate. Triple labeling of extracellular citrate exceeded that of double labeling from [U-(13)C]glucose. This was not the case when lactate was the labeled precursor. These results indicate that pyruvate carboxylation in biosynthesis of releasable citrate was less prominent from lactate compared with glucose. As observed in the case of extracellular citrate, triple labeling of intracellular aspartate was higher than double labeling when [U-(13)C]glucose was the precursor, but not with [U-(13)C]lactate as precursor. The pattern of labeling in citrate was different intra- and extracellularly and the extent of labeling extracellularly was 10 times higher using [U-(13)C]glucose compared with [U-(13)C]lactate. However, the intracellular citrate labeling from [U-(13)C]glucose only exceeded that originating from labeled lactate by a factor of two. This is in contrast to the labeling pattern obtained for glutamine, since intracellularly this was equally prominent using [U-(13)C]glucose and [U-(13)C]lactate as substrates. Moreover, extracellularly the labeling was only slightly higher when using [U-(13)C]glucose compared with [U-(13)C]lactate. Intracellular glutamate and extracellular glutamine exhibited similar incorporation patterns with regard to double compared with triple labeling and the extent of incorporation of label from [U-(13)C]lactate compared with [U-(13)C]glucose. It should be noted that the main intracellular pools of citrate and glutamine were compartmentalized; i.e., releasable citrate and glutamine exhibited a labeling pattern distinctly different from that of their intracellular pools. Moreover, carboxylation of pyruvate using glucose as the precursor was more important for biosynthesis of releasable glutamine and citrate, compared with their intracellular pools. Based on the results a model of multiple compartments is suggested. The compartments differ with regard to utilization of lactate and glucose, synthetic pathways for TCA cycle intermediates and amino acids, particularly citrate and glutamine, as well as the contents of different metabolites.

Amino Acids↗
PubMed1996

Surface signaling in transcriptional regulation of the ferric citrate transport system of Escherichia coli: mutational analysis of the alternative sigma factor FecI supports its essential role in fec transport gene transcription.

Ferric citrate induces transcription of the ferric citrate transport genes (fec) in escherichia coli by binding to the outer membrane receptor protein FecA without entering the cell. The signal elicited by ferric citrate crosses the outer membrane via TonB, ExbB, and ExbD. FecR transmits the signal across the cytoplasmic membrane and activates FecI located in the cytoplasm. FecI belongs to a subgroup of sigma factors that respond to extracytoplasmic stimuli. Chromosomal insertion and deletion mutations were generated in fecI; the resulting mutants were totally devoid of FecA production and fecB-lacZ expression. Iron starvation did not derepress fec transport gene transcription in fecI mutants. Missense point mutations were generated in the predicted helix-turn-helix motif of FecI to examine its role in transcription initiation. Replacement of glutamate by alanine (E141A) at the third position in the first helix reduced the residual activity of FecI in the absence of ferric citrate to 30% of the wild-type level, but induced fec transcription almost normally n the presence of ferric citrate. Mutant FecI(K145E) displayed 156% of the activity of wild-type FecI in the absence of ferric citrate and conferred full induction by ferric citrate. Mutant FecI(K155E), which has a mutation in the second helix, showed 9% of the wild-type activity in the presence of ferric citrate and 78% in the absence of ferric citrate. The reduced activity of FecI(K155E) was also shown in vitro by DNA binding assays with cell lysates; in gel retardation experiments FecI(K155E) reduced the electrophoretic mobility of fecA promoter-containing DNA less than did wild-type FecI. fecI is not autoregulated, as demonstrated by the lack of FecI-induced fecI-lacZ expression in vivo and by the lack of specific fecI transcription in vitro. Instead, formation of fecI mRNA requires sigma 70. We conclude that transcription of the fec transport genes is regulated by FecI, which responds to ferric citrate via FecR. fecI and fecR co-transcription is inhibited by the iron-loaded Fur repressor, which then results in a low level of transcription of the fec transport genes.

Amino Acid Sequence↗
PubMed1989

Peri-implantation phase endometrial estrogen and progesterone receptors: effect of ovulation induction with clomiphene citrate.

The effects of clomiphene citrate on endometrial nuclear estradiol receptors and progesterone receptors were examined in 10 normal women during an untreated cycle (control) and during treatment with 50 mg clomiphene citrate and 150 mg clomiphene citrate daily on days 5 through 9. Concentrations and binding constants of the receptors were determined in endometrium obtained 8 to 12 days after midcycle luteinizing hormone surge. Scatchard plots for both estrogen receptors and progesterone receptors were linear, indicating only one type of high-affinity binding sites. In control cycles, estrogen receptor levels (mean +/- SEM) were 199.6 +/- 23.1 fmol/mg deoxyribonucleic acid, (n = 8) and were not significantly different from either 50 mg clomiphene citrate (180.5 +/- 19.1 fmol/mg deoxyribonucleic acid, n = 6) or 150 mg clomiphene citrate (194.3 +/- 35.2 fmol/mg deoxyribonucleic acid, n = 4). Similarly, the dissociation constants were unaffected by clomiphene citrate treatment. The concentrations of progesterone receptors in the control cycles (613 +/- 31 fmol/mg deoxyribonucleic acid, n = 5) and treatment cycles (50 mg clomiphene citrate -652.8 +/- 121 fmol/mg deoxyribonucleic acid, n = 6; 150 mg clomiphene citrate -592.6 +/- 31 fmol/mg deoxyribonucleic acid, n = 7) were also not significantly different. Clomiphene citrate also did not affect dissociation constants for progesterone receptors. Therefore, ovulation induction with clomiphene citrate apparently did not affect peri-implantation phase endometrial estrogen receptors and progesterone receptors or their respective binding constants.

Adult↗
PubMed2006

Transport and toxic mechanism for aluminum citrate in human neuroblastoma SH-SY5Y cells.

Aluminum (Al) is thought to be a risk factor for neurodegenerative disorders, but the molecular mechanism has been not clarified yet. In this study, we examined how a transport system handled transport of Al citrate, the major Al species in brain, and effect of Al citrate treatment on expression of the transporter and on susceptibility to oxidative stress in human neuroblastoma SH-SY5Y cells. Uptake of Al citrate by the cells was temperature- and concentration-dependent, and inwardly-directed Na(+)-gradient-independent. Simultaneous application and preloading of L-cystine or L-glutamate inhibited and stimulated, respectively, the Al citrate uptake by SH-SY5Y cells, demonstrating kinetically that Na(+)-independent L-cystine/L-glutamate exchanger, system Xc(-), is involved in its uptake. When the cells were treated with Al citrate, but not citrate, for 2 weeks, but not a day, the expression of the transporter was decreased. Although the cell viability and glutathione content of the cells were not altered by the treatment with Al citrate alone, the number of dead cells among the Al citrate-treated cells increased on exposure to oxidative stress caused by a glucose deprivation/reperfusion treatment. These findings demonstrate that Al citrate is a substrate for system Xc(-), and that chronic treatment with Al citrate causes downregulation of the transporter and increases the vulnerability of the cells to oxidative stress without a direct effect on the viability or GSH content.

Aluminum↗
PubMed2002

Human Na+ -coupled citrate transporter: primary structure, genomic organization, and transport function.

This paper describes the cloning and functional characterization of the human Na(+)-coupled citrate transporter (NaCT). The cloned human NaCT shows 77% sequence identity with rat NaCT. The nact gene is located on human chromosome 17 at p12-13. NaCT mRNA is expressed most predominantly in the liver, with moderate expression detectable in the brain and testis. When functionally expressed in mammalian cells, human NaCT mediates the Na(+)-coupled transport of citrate. Studies with several monocarboxylates, dicarboxylates, and tricarboxylates show that the transporter is selective for citrate with comparatively several-fold lower affinity for other intermediates of citric acid cycle. The Michelis-Menten constant for citrate is approximately 650 microM. The activation of citrate transport by Na(+) is sigmoidal, suggesting involvement of multiple Na(+) ions in the activation process. The transport process is electrogenic. This represents the first plasma membrane transporter in humans that mediates the preferential entry of citrate into cells. Citrate occupies a pivotal position in many important biochemical pathways. Among various citric acid cycle intermediates, citrate is present at the highest concentrations in human blood. The selectivity of NaCT towards citrate and its predominant expression in the liver suggest that this transporter may facilitate the utilization of circulating citrate for the generation of metabolic energy and for the synthesis of fatty acids and cholesterol.

Amino Acid Sequence↗
PubMed2004

pH-dependent isolations and spectroscopic, structural, and thermal studies of titanium citrate complexes.

Titanium(IV) citrate complexes (NH(4))(2)[Ti(H(2)cit)(3)].3H(2)O (1), (NH(4))(5)[Fe(H(2)O)(6)][Ti(H(2)cit)(3)(Hcit)(3)Ti].3H(2)O (2), Ba(2)[Ti(H(2)cit)(Hcit)(2)].8H(2)O (3), and Ba(3)(NH(4))(7)[Ti(cit)(3)H(3)(cit)(3)Ti].15H(2)O (4) (H(4)cit = citric acid) were isolated in pure form from the solutions of titanium(IV) citrate with various countercations. The isolated complexes were characterized by elemental analyses, IR spectra, and (1)H NMR and (13)C NMR spectra. The formation of titanium(IV) citrate complexes depends mainly on the pH of the solutions, that is, pH 1.0-2.8 for the formation of ammonium titanium(IV) citrate 1, pH 2.5-3.5 for ammonium iron titanium(IV) citrate 2, pH 2.8-4.0 for dibarium titanium(IV) citrate 3, and pH 5.0-6.0 for ammonium barium titanium(IV) citrate 4. X-ray structural analyses revealed that complexes 2-4 featured three different protonated forms of bidentate citrate anions that chelate to the titanium(IV) atom through their negatively charged alpha-alkoxyl and alpha-carboxyl oxygen atoms. This is consistent with the large downfield shifts of the (13)C NMR spectra for the carbon atoms bearing the alpha-alkoxyl and alpha-carboxyl groups. The typical coordination modes of the barium atoms in complexes 3 and 4 are six-coordinated, with three alpha-alkoxyl groups and three beta-carboxyl groups of citrate ions. The strong hydrogen bonding between the beta-carboxylic acid and the beta-carboxyl groups [2.634(8) A for complex 2, 2.464(7) A for complex 3, and 2.467(7) A for complex 4] may be the key factor for the stabilization of the citrate complexes. The decomposition of complex 3 results in the formation of a pure dibarium titanate phase and 4 for the mixed phases of dibarium titanate and barium titanate at 1000 degrees C.

Citric Acid↗
PubMed1998

In vitro modulation of proliferation and melanization of melanoma cells by citrate.

B16/F10 murine melanoma cells were grown for 24 and 36 h in Dulbecco's modified Eagle medium in presence of 10-20 mM trisodium citrate. The intracellular melanin concentration and the melanin secreted in the extracellular medium was estimated. It is observed that 20 mM citrate stimulates extracellular melanin secretion in B16/F10 melanoma cells by 200% at 36 h treatment. The intracellular melanin content increased by 90%. This stimulatory effect of citrate was totally abolished when these cells were grown in presence of 1 mM phenyl thiourea, a specific inhibitor of tyrosinase activity. Citrate (0.1-5 mM) had no effect on dopa oxidase activity either at pH 5.0 or at pH 6.8. There was no increase in the tyrosinase specific activity in presence of citrate. The increased melanin synthesis was shown to be due to stimulation of cellular tyrosine hydroxylase activity by citrate. It has been suggested that enhanced melanin synthesis results in an increased production of metabolites that are toxic to the growth of melanoma cells. We have studied the effect of citrate on cellular proliferation. Following 24 and 36 h treatment with citrate, the cells exhibited a dose-dependent decrease in proliferation. In presence of 20 mM citrate the cell number was only up to 50% of the control cultures after 36 h of incubation. The growth retardation was not due to cytotoxicity. Citrate, a natural metabolite, is a unique molecule which may be involved in the regulation of melanin biosynthetic pathway, since it enhances melanogenesis by increasing the hydroxylase activity of tyrosinase which is the regulatory enzyme of this pathway. These observations add further support to the critical role of intramelanosomal pH in regulation of melanogenesis.

Animals↗
PubMed2003

Citrate oscillates in liver and pancreatic beta cell mitochondria and in INS-1 insulinoma cells.

Oscillations in citric acid cycle intermediates have never been previously reported in any type of cell. Here we show that adding pyruvate to isolated mitochondria from liver, pancreatic islets, and INS-1 insulinoma cells or adding glucose to intact INS-1 cells causes sustained oscillations in citrate levels. Other citric acid cycle intermediates measured either did not oscillate or possibly oscillated with a low amplitude. In INS-1 mitochondria citrate oscillations are in phase with NAD(P) oscillations, and in intact INS-1 cells citrate oscillations parallel oscillations in ATP, suggesting that these processes are co-regulated. Oscillations have been extensively studied in the pancreatic beta cell where oscillations in glycolysis, NAD(P)/NAD(P)H and ATP/ADP ratios, plasma membrane electrical activity, calcium levels, and insulin secretion have been well documented. Because the mitochondrion is the major site of ATP synthesis and NADH oxidation and the only site of citrate synthesis, mitochondria need to be synchronized for these factors to oscillate. In suspensions of mitochondria from various organs, most of the citrate is exported from the mitochondria. In addition, citrate inhibits its own synthesis. We propose that this enables citrate itself to act as one of the cellular messengers that synchronizes mitochondria. Furthermore, because citrate is a potent inhibitor of the glycolytic enzyme phosphofructokinase, the pacemaker of glycolytic oscillations, citrate may act as a metabolic link between mitochondria and glycolysis. Citrate oscillations may coordinate oscillations in mitochondrial energy production and anaplerosis with glycolytic oscillations, which in the beta cell are known to parallel oscillations in insulin secretion.

Animals↗
PubMed2005

A link between citrate and proton release by proteoid roots of white lupin (Lupinus albus L.) grown under phosphorus-deficient conditions?

White lupin (Lupinus albus L.) is able to acclimate to phosphorus deficiency by forming proteoid roots that release a large amount of citric acid, resulting in the mobilization of sparingly soluble soil phosphate in the rhizosphere. The mechanisms responsible for the release of organic acids have not been fully elucidated. In this study, we focused on the link between citrate and malate release and the release of H+ and other inorganic ions by proteoid roots of white lupin. The release of citrate was closely correlated with the release of H+, K+, Na+ and Mg2+, but not with that of Ca2+. The stoichiometric relationships between citrate release and the release of H+, K+, Na+ and Mg2+ were 1 : 1.3, 1 : 2.1, 1 : 1.5 and 1 : 0.47, respectively. Similar correlations were found between exudation of malate and cations. During 30 min incubation, fusicoccin addition stimulated H+ and malate release, but not citrate release. A concomitant stimulation of H+, malate and citrate release was measured after 60 min incubation. Vanadate inhibited the release of H+ and malate, but not that of citrate. Anthracene-9-carboxylic acid, an anion channel blocker, caused a concomitant decrease in release of citrate, malate and H+. We conclude that for export of citrate across the plasma membrane of proteoid root cells, H+ release is not strictly related to citrate release. Other cations such as K+ and Na+ can also serve as counterions for citrate release. In contrast, malate release shows a strong H+ release dependency.

Anions↗
PubMed2001

Increased total to ionized calcium ratio during continuous venovenous hemodialysis with regional citrate anticoagulation.

BACKGROUND: Citrate anticoagulation is commonly used for continuous venovenous hemodialysis (CVVHD) to minimize the risk of bleeding complications. We have previously reported a liver failure patient undergoing citrate-based CVVHD with elevated serum total to ionized calcium ratio. Diminished liver metabolism of citrate with resultant elevated systemic citrate was thought to be the cause. METHODS: To determine the incidence and clinical significance of an elevated total to ionized calcium ratio during citrate-based CVVHD, 161 patients undergoing citrate-based CVVHD were screened for the presence of an elevated total to ionized calcium ratio (the subset with increased total to ionized calcium ratio comprised the study group). Because all patients in the study group had liver failure, two control groups of patients with normal total to ionized calcium ratios were formed-those without liver failure (control I) and those with liver failure (control II). RESULTS: An elevated total to ionized calcium ratio was detected in 12% of all patients. Thirty-three percent of liver failure patients demonstrated an elevated total to ionized calcium ratio. The study group demonstrated significantly higher mean total calcium levels, significantly lower mean ionized calcium levels, and significantly higher mean total to ionized calcium ratios than controls. As a result, the study group also had significantly increased mean calcium chloride replacement requirements in comparison with controls. The mean calcium to citrate infusion ratio was elevated in the study group in comparison with controls. An elevated total to ionized calcium ratio was associated with increased mortality in comparison with controls. No patients suffered complications from ionized hypocalcemia or elevated serum total calcium. CONCLUSIONS: Systemic citrate accumulation as evidenced by an elevated total to ionized calcium ratio occurs commonly in patients requiring CVVHD using citrate-based regional anticoagulation. Observing changes in the total to ionized calcium ratio can aid in early detection of patients with hepatic failure who are unable to appropriately metabolize citrate and will require calcium chloride infusion rates significantly above normal.

Adult↗
PubMed1966

Iron translocation I. Plant culture, exudate sampling, iron-citrate analysis.

Plant culture, exudate sampling, and analytical methods designed to ascertain the form of iron translocated are presented.Restoration of iron to sunflower plants precultured at different Fe levels resulted in exudate iron concentrations ranging from 0.2 to 31 x 10(-5)m. Citrate was from 3 to 89 x 10(-5)m. Iron and citrate were highest in exudates from iron-deficient plants. Citrate/Fe ratios were between 1 and 3 for exudates of deficient plants. Exudate from normal plants gave a citrate/Fe ratio of 15.Malate, iron, and a fraction of the citrate in stem exudates migrated electrophoretically to similar positions in acetate buffer. Extracts of narrow bands from the iron-containing areas gave curves suggesting that citrate bound the iron. Citrate that was not combined with iron migrated in a slower band. The effect of iron on citrate migration was confirmed in several related experiments.The stability of Fe-citrate was demonstrated electrophoretically in malate buffer. Citrate retained iron against malate.Data given in this paper indicate that citrate binds iron in sunflower exudate. The data suggest that citrate carries iron in intact plants.

Journal Article↗
PubMed1982

Citrate transport in corn mitochondria.

Citrate uptake by corn mitochondria (Zea mays L. B73 x Mol9) was investigated by osmotic swelling and [(14)C]citrate accumulation. Uptake driven by passive influx, ammonium gradients, and respiration was followed. There was no requirement for phosphate and/or malate to secure citrate uptake, although under some conditions these additives were promotive. Inhibition of the phosphate and dicarboxylate carriers did not eliminate citrate uptake. Citrate(in)/malate(out) exchange occurs, but at a rate too slow to account for observed citrate uptake, and depletion of endogenous malate only reduced citrate uptake by 38%. It was concluded that citrate can be rapidly accumulated by a mechanism other than by exchange for dicarboxylates. The effect of uncoupler on respiration-driven [(14)C]citrate accumulation, and studies of passive swelling using ionophores and uncouplers indicated that the major avenue of citrate uptake is by H(+)/citrate co-transport with a pH optimum near 4.5. The in vivo role of this mechanism is not yet understood.

Journal Article↗
PubMed1998

Purification of Leuconostoc mesenteroides citrate lyase and cloning and characterization of the citCDEFG gene cluster.

A citrate lyase (EC 4.1.3.6) was purified 25-fold from Leuconostoc mesenteroides and was shown to contain three subunits. The first 42 amino acids of the beta subunit were identified, as well as an internal peptide sequence spanning some 20 amino acids into the alpha subunit. Using degenerated primers from these sequences, we amplified a 1.2-kb DNA fragment by PCR from Leuconostoc mesenteroides subsp. cremoris. This fragment was used as a probe for screening a Leuconostoc genomic bank to identify the structural genes. The 2.7-kb gene cluster encoding citrate lyase of L. mesenteroides is organized in three open reading frames, citD, citE, and citF, encoding, respectively, the three citrate lyase subunits gamma (acyl carrier protein [ACP]), beta (citryl-S-ACP lyase; EC 4.1.3.34), and alpha (citrate:acetyl-ACP transferase; EC 2.8.3.10). The gene (citC) encoding the citrate lyase ligase (EC 6.2.1.22) was localized in the region upstream of citD. Protein comparisons show similarities with the citrate lyase ligase and citrate lyase of Klebsiella pneumoniae and Haemophilus influenzae. Downstream of the citrate lyase cluster, a 1.4-kb open reading frame encoding a 52-kDa protein was found. The deduced protein is similar to CitG of the other bacteria, and its function remains unknown. Expression of the citCDEFG gene cluster in Escherichia coli led to the detection of a citrate lyase activity only in the presence of acetyl coenzyme A, which is a structural analog of the prosthetic group. This shows that the acetyl-ACP group of the citrate lyase form in E. coli is not complete or not linked to the protein.

Acyl Carrier Protein↗