Effect of digoxin on global respiratory muscle strength after cholecystectomy: a double blind study.
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BACKGROUND: Upper abdominal surgery has been shown to impair the function of the respiratory muscles. In addition, controversial results have been reported concerning the effect of digoxin on the diaphragm. The aim of this study was to investigate further the mechanism(s) of respiratory muscle dysfunction after cholecystectomy and the effect of digoxin on the impaired respiratory muscle function. METHODS: Twenty three patients (four men) were studied before and 48 hours after surgery. Eleven received digoxin and 12 placebo. Respiratory muscle strength was assessed 48 hours after surgery by measuring mouth pressure during maximum static inspiratory (PImax) and expiratory (PEmax) efforts before and after 90 minutes of intravenous administration of 0.25 mg digoxin in a double blind, placebo controlled fashion. In addition, spirometric and pain measurements were performed. RESULTS: Postoperatively (+48 h) PImax and PEmax decreased significantly (p<0.01) from their preoperative values in both groups by a similar degree. After administration of digoxin or placebo only the digoxin group showed a significant increase in both PImax (p<0.02) and PEmax (p<0.05) with a mean increase of 15% for PImax and 12.3% for PEmax. The mean difference in PImax (DeltaPImax) and PEmax (DeltaPEmax) between the digoxin and placebo groups was 1.01 (95% CI 0.28 to 2.2) and 1.05 (95% CI 0.04 to 2.4), respectively. Estimates of postoperative pain did not differ between the two groups. Spirometric indices showed a similar restrictive defect postoperatively in both groups but did not change after digoxin or placebo. CONCLUSION: Digoxin improves the impaired global strength of the inspiratory and expiratory muscles after cholecystectomy and this may be clinically relevant. Muscle contractility could play a part in this impairment. (+info)
Haemodynamic effects of the antiarrhythmic quaternary ammonium compound QX-572 in man.
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The haemodynamic effects of N, N-bis(phenyl-carbamoylmethyl) dimethylammonium chloride (QX-572) in man were studied. A controlled study was performed to rule out a possible influence of the catheterization procedure as such on the results. Ten patients with mild to moderate aortic regurgitation were studied: based on clinical data the patients were divided into 2 groups of 5. Randomly it was decided that one group should constitute a control group receiving saline while the second group received QX-572 , MG/KG BODY WEIGHT. In both groups the administration was performed as a slow intravenous infusion during 30 minutes. Heart rate, pressures in brachial artery and right atrium, cardiac output, stroke volume, and systemic vascular resistance were determined before, during, and up to 30 minutes after completion of placebo or QX-572. These variable remained stable in the control group while QX-572 produced an increase in heart rate most pronounced at the end of the infusion period. A transient decrease in systolic and mean brachial artery pressure during the infusion, and during the same period a decrease in right atrial pressure. Cardiac output and systemic vascular resistance were unchanged by QX-572 but they were not measured during the infusion when the changes in pressures were most pronounced. QX-572 was thought to act as a peripheral vasodilator during the infusion. Left ventricular contractility was studied by means of pressure curves obtained from a catheter tip manometer placed in the left ventricle. The first derivative of the isovolumic left ventricular pressure at the highest level (45mmHg) common to all patients was used (dp/dt-45). No significant difference could be observed when comparing mean changes of dp/dt-45 for the two groups. In the control group there was a slight but significant increase in dp/dt-45 during the time of observation. In the QX-572 group the results varied between individuals. Two of the patients differed from all other patients in the control and QX-572 groups showing a decrease in dp/dt-45 which, when most pronounced at the end of the infusion period, was -31 and -28 per cent of the preinfusion levels, respectively. This decrease probably reflects reduction of contractility. It was concluded that QX-572 in a dose of 8 mg/kg body weight did not have any major haemodynamic drawbacks. (+info)
Oatp2 mediates bidirectional organic solute transport: a role for intracellular glutathione.
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One member of the OATP family of transporters, rat Oatp1, functions as an anion exchanger that is driven in part by the glutathione (GSH) electrochemical gradient, indicating that other OATP-related transporters may also be energized by this mechanism. The present study examined whether rat Oatp2 is also an anion exchanger, and, if so, whether it is energized by the GSH electrochemical gradient. As with Oatp1, uptake of 10 microM [(3)H]taurocholate in Oatp2-expressing Xenopus laevis oocytes was trans-stimulated by intracellular 0.2 mM unlabeled taurocholate, indicating bidirectional transport. Interestingly, [(3)H]taurocholate uptake in Oatp2-expressing oocytes was also trans-stimulated when oocytes were preloaded with GSH, S-methylglutathione, S-sulfobromophthalein-glutathione, S-dinitrophenyl glutathione, or ophthalmic acid (a GSH analog) but not by glutarate or N-acetylcysteine, suggesting that GSH derivatives and conjugates may function as intracellular substrates for Oatp2. Support for this hypothesis was provided by the demonstration of enhanced [(3)H]GSH and [(3)H]S-(2,4-dinitrophenyl)-glutathione efflux in Oatp2-expressing oocytes. However, in contrast to Oatp1, extracellular GSH failed to cis-inhibit uptake of [(3)H]taurocholate or [(3)H]digoxin in Oatp2-expressing oocytes, indicating that the stimulatory effect of high intracellular GSH concentrations is not due to a coupled exchange mechanism. Taken together, the results indicate that Oatp2 mediates bidirectional transport of organic anions by a GSH-sensitive facilitative diffusion mechanism and suggest that this transporter may play a role in cellular export of specific organic molecules. (+info)
Maximal intestinal absorption of digoxin, and its relation to steady state plasma concentration.
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In a group of 8 volunteers, peak plasma digoxin concentrations and areas under 80-hour plasma concentration curves were significantly greater after 1 mg digoxin in paediatric elixir than after 4 0,25 mg tablets. Mean cumulative urinary excretion of digoxin over 12 days was 46.4 per cent after tablets, 53.6 per cent after elixir, and 70.8 per cent after intravenous injection. Mean percentage absorption was estimated to be 63 per cent from tablets and 75 per cent from elixir, but considerable between-subject variation was noted. Individual estimates of percentage absorption were significantly correlated with plasma concentrations in the steady state. Computer programmes to relate steady state plasma concentration to oral digoxin dosage take no account of absorptive capacity, are limited to gross approximations, and cannot replace determination of plasma concentration to assess the degree of digitalization. (+info)
MDR3 P-glycoprotein, a phosphatidylcholine translocase, transports several cytotoxic drugs and directly interacts with drugs as judged by interference with nucleotide trapping.
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The human MDR3 gene is a member of the multidrug resistance (MDR) gene family. The MDR3 P-glycoprotein is a transmembrane protein that translocates phosphatidylcholine. The MDR1 P-glycoprotein related transports cytotoxic drugs. Its overexpression can make cells resistant to a variety of drugs. Attempts to show that MDR3 P-glycoprotein can cause MDR have been unsuccessful thus far. Here, we report an increased directional transport of several MDR1 P-glycoprotein substrates, such as digoxin, paclitaxel, and vinblastine, through polarized monolayers of MDR3-transfected cells. Transport of other good MDR1 P-glycoprotein substrates, including cyclosporin A and dexamethasone, was not detectably increased. MDR3 P-glycoprotein-dependent transport of a short-chain phosphatidylcholine analog and drugs was inhibited by several MDR reversal agents and other drugs, indicating an interaction between these compounds and MDR3 P-gp. Insect cell membranes from Sf9 cells overexpressing MDR3 showed specific MgATP binding and a vanadate-dependent, N-ethylmaleimide-sensitive nucleotide trapping activity, visualized by covalent binding with [alpha-(32)P]8-azido-ATP. Nucleotide trapping was (nearly) abolished by paclitaxel, vinblastine, and the MDR reversal agents verapamil, cyclosporin A, and PSC 833. We conclude that MDR3 P-glycoprotein can bind and transport a subset of MDR1 P-glycoprotein substrates. The rate of MDR3 P-glycoprotein-mediated transport is low for most drugs, explaining why this protein is not detectably involved in multidrug resistance. It remains possible, however, that drug binding to MDR3 P-glycoprotein could adversely affect phospholipid or toxin secretion under conditions of stress (e.g. in pregnant heterozygotes with one MDR3 null allele). (+info)
Cardiac glycosides stimulate Ca2+ increases and apoptosis in androgen-independent, metastatic human prostate adenocarcinoma cells.
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Cardiac glycosides are used clinically to increase contractile force in patients with cardiac disorders. Their mechanism of action is well established and involves inhibition of the plasma membrane Na+/K+-ATPase, leading to alterations in intracellular K+ and Ca(2+) levels. Here, we report that the cardiac glycosides oleandrin, ouabain, and digoxin induce apoptosis in androgen-independent human prostate cancer cell lines in vitro. Cell death was associated with early release of cytochrome c from mitochondria, followed by proteolytic processing of caspases 8 and 3. Oleandrin also promoted caspase activation, detected by cleavage poly(ADP-ribose) polymerase and hydrolysis of a peptide substrate (DEVD-pNA). Comparison of the rates of apoptosis in poorly metastatic PC3 M-Pro4 and highly metastatic PC3 M-LN4 subclones demonstrated that cell death was delayed in the latter because of a delay in mitochondrial cytochrome c release. Single-cell imaging of intracellular Ca(2+) fluxes demonstrated that the proapoptotic effects of the cardiac glycosides were linked to their abilities to induce sustained Ca(2+) increases in the cells. Our results define a novel activity for cardiac glycosides that could prove relevant to the treatment of metastatic prostate cancer. (+info)
Probing ligand protein binding equilibria with fluorescence fluctuation spectroscopy.
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We examine the binding of fluorescent ligands to proteins by analyzing the fluctuation amplitude g(0) of fluorescence fluctuation experiments. The normalized variance g(0) depends on the molecular brightness and the concentration of each species in the sample. Thus a single g(0) measurement is not sufficient to resolve individual species. Titration of the ligand with protein establishes the link between molecular brightness and concentration by fitting g(0) to a binding model and allows the separation of species. We first apply g(0) analysis to binary dye mixtures with brightness ratios of 2 and 4 to demonstrate the feasibility of this technique. Next we consider the influence of binding on the fluctuation amplitude g(0). The dissociation coefficient, the molecular brightness ratio, and the stochiometry of binding strongly influence the fluctuation amplitude. We show that proteins with a single binding site can be clearly differentiated from proteins with two independent binding sites. The binding of fluorescein-labeled digoxigenin to a high-affinity anti-digoxin antibody was studied experimentally. A global analysis of the fluctuation amplitude and the fluorescence intensity not only recovered the dissociation coefficient and the number of binding sites, but also revealed the molecular heterogeneity of the hapten-antibody complex. Two species were used to model the molecular heterogeneity. We confirmed the molecular heterogeneity independently by fluorescence lifetime experiments, which gave fractional populations and molecular brightness values that were virtually identical to those of the g(0) analysis. The identification and characterization of molecular heterogeneity have far-reaching consequences for many biomolecular systems. We point out the important role fluctuation experiments may have in this area of research. (+info)
Ouabain augments Ca(2+) transients in arterial smooth muscle without raising cytosolic Na(+).
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Ouabain and other cardiotonic steroids (CTS) inhibit Na(+) pumps and are widely believed to exert their cardiovascular effects by raising the cytosolic Na(+) concentration ([Na(+)](cyt)) and Ca(2+). This view has not been rigorously reexamined despite evidence that low-dose CTS may act without elevating [Na(+)](cyt); also, it does not explain the presence of multiple, functionally distinct isoforms of the Na(+) pump in many cells. We investigated the effects of Na(+) pump inhibition on [Na(+)](cyt) (with Na(+) binding benzofuran isophthalate) and Ca(2+) transients (with fura 2) in primary cultured arterial myocytes. Low concentrations of ouabain (3-100 nM) or human ouabain-like compound or reduced extracellular K(+) augmented hormone-evoked mobilization of stored Ca(2+) but did not increase bulk [Na(+)](cyt). Augmentation depended directly on external Na(+), but not external Ca(2+), and was inhibited by 10 mM Mg(2+) or 10 microM La(3+). Evoked Ca(2+) transients in pressurized small resistance arteries were also augmented by nanomolar ouabain and inhibited by Mg(2+). These results suggest that Na(+) enters a tiny cytosolic space between the plasmalemma (PL) and the adjacent sarcoplasmic reticulum (SR) via an Mg(2+)- and La(3+)-blockable mechanism that is activated by SR store depletion. The Na(+) and Ca(2+) concentrations within this space may be controlled by clusters of high ouabain affinity (alpha3) Na(+) pumps and Na/Ca exchangers located in PL microdomains overlying the SR. Inhibition of the alpha3 pumps by low-dose ouabain should raise the local concentrations of Na(+) and Ca(2+) and augment hormone-evoked release of Ca(2+) from SR stores. Thus the clustering of small numbers of specific PL ion transporters adjacent to the SR can regulate global Ca(2+) signaling. This mechanism may affect vascular tone and blood flow and may also influence Ca(2+) signaling in many other types of cells. (+info)