Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: DrugBank:EXPT00514 (Amiloride)
 1,513 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The teleostean gill is characterized by an exceptionally low permeability to water. Water moves along the osmotic gradient across the gill, being gained in fresh water and lost in sea water. Coupling of water movement to solute movement has not been reported. In fresh water, the gill is the site of independent active uptake of sodium and chloride. Na+ uptake is coupled to H+ or NH4+ excretion, Cl- uptake to HCO3- excretion. Amiloride blocks sodium transport and thiocyanate inhibits the chloride pump. In sea water, sodium and chloride exchanges across the gill are about 100 times faster than in fresh water, up to 100% of the internal sodium or chloride being exchanged per hour. Chloride is actively excreted, while sodium movement may well be passive. The chloride pump is associated with a mechanism for Na/K exchange; both pump and Na/K exchange are blocked by thiocyanate and possibly by ouabain. Three enzymes are involved in the ionic pumps: carbonate dehydratase (EC 4.2.1.1; carbonic anhydrase), sodium/potassium-stimulated adenosine-triphosphatase (EC 3.6.1.3, ATPase) and anion-stimulated ATPase. Specialized cells ('chloride cells') are presumably the site of the active transport.
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PMID:Transport of ions and water across the epithelium of fish gills. 0 38

The interaction of amiloride and LiCl administration on renal HCO3 handling was studied in hydropenic rats. Amiloride administration resulted in a significant increase in Na, Cl, and HCO3 excretion, whereas K excretion decreased significantly. LiCl administration resulted in a significant increase in Na, Cl, K, and HCO3 excretion. LiCl administration to animals receiving amiloride led to a significant increase in HCO3 excretion but failed to cause an increase in Na or K excretion. Addition of amiloride to animals receiving LiCl resulted in a significant increase in Na and HCO3 excretion. The net increase in fractional HCO3 excretion seen in this group was greater than that seen in all other groups. The finding that the net increase in FEHCO3 was greater in animals receiving amiloride after administration of LiCl than in animals receiving LiCl after amiloride administration indicates that amiloride blunted the effect of LiCl on HCO3 excretion. Administration of amiloride to both normal rats and to rats infused with Li during HCO3 administration resulted in a significant decrease in U-B Pco2 which could not be explained by the decrease in urine HCO3 concentration. These data demonstrate that amiloride inhibits distal acidification in vivo. LiCl administration also resulted in a decrease in U-B Pco2 which could be explained by the decrease in urine HCO3 concentration. LiCl administration also resulted in a decrease in TcH2O which could be prevented by prior administration of amiloride. These data indicate that amiloride blunts the effect of LiCl on urinary acidification, an effect similar to that observed on urinary concentration. These data suggest that the effect of Li on urinary acidification is in part dependent on Li entry into the cell.
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PMID:Interaction of amiloride and lithium on distal urinary acidification. 3 80

It is not known whether factors other than Na transport are involved in generating the electrical potential difference (PD) across the human colonic wall. Therefore, experiments were performed in which the effect of amiloride on PD and ion transport was evaluated in the in vitro short-circuited human colon. In control periods the short-circuit current (Isc) was 2.9 +/- 0.3 (mean +/- S.E.M.) muEq per hr per cem2, while the corresponding net transfer of Na and Cl was 4.6 +/- 0.4 and 1.4 +/- 0.1 respectively. The residual flux was insignificantly different from zero. Amiloride caused a prompt, but reversible, decrease in Isc, PD, and conductance when added to the mucosal sie,dbut only a relatively small reduction of the mucosa to serosa fluxes of Na occurred. Bidirectional Cl fluxes were unchanged while the residual flux increased significantly. It is proposed, therefore, that some ions other than Cl (presumably mucosa to serosa fluxes of H and/or serosa to mucosa fluxes of HCO3) are the main counter ions for actively transported Na in the large bowel. Experiments performed in vivo showed that the rectal PD decreased exponentially from -46 mV +/- 0.8 TO -27 MV +/- 0.3 (mean +/- S.E.M.) following rectal instillation of 10-3 M amiloride. The half-time required for this effect was less than 13 seconds.
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PMID:Effect of amiloride on electrical activity and electrolyte transport in human colon. 83 61

1. The electrical properties and the active transport processes of the isolated urinary bladder of the urodele, Amphiuma means, were studied by mounting this tissue as a flat sheet between two halves of a lucite chamber. The mean transepithelial potential difference was 70-2 +/- 2-3 mV (serosa positive), the mean short-circuit current was 10-9 +/- 0-5 micrionA/mg of dry weight and the mean transepithelial d.c. resistance was 6540 +/- 374 omega mg of dry weight. 2. The short-circuit current (Isc) accounted for 92% of the net 22Na+ flux from the mucosa to the serosa. The difference resulted from a transport of 36Cl- in the same direction as sodium. 3. The active sodium transport exhibited typical saturation kinetics, having a Km of 15-4 m-equiv/l. and approaching zero order at 60-70 m-equiv/l. The transepithelial potential difference increased linearly with the log of the mucosal sodium concentration at a rate of 50-3 mV per tenfold concentration change. 4. In the absence of the major anions (HCO3- and Cl-) from the bathing solutions, the electrical properties and the sodium influx decreased to less than 40% of their control values. The presence of only one of these two anions in the serosal bathing solution was sufficient to maintain these parameters. 5. Amiloride (10(-5)M) and ouabain (10(-6)M) inhibited the sodium transport 97% and 85% respectively. Amphotericin B (10(-6)M) stimulated the sodium transport 47%. Furosemide (10(-3)M) inhibited the chloride transport 43%. The sodium transport was insensitive to the action of two enurohypophyseal peptides tested, lysine-vasotocin and pitocin.
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PMID:The electrical properties and active ion transport across the urinary bladder of the urodele, Amphiuma means. 85 Jan 64

1. Intracellular pH (pHi) was recorded ratiometrically in isolated guinea-pig ventricular myocytes using the pH-sensitive fluoroprobe, carboxy-SNARF-1 (carboxy-seminaphthorhodafluor). 2. Following an intracellular acid load (10 mM NH4 Cl removal), pHi recovery in HEPES-buffered Tyrode solution was inhibited by 1.5 mM amiloride (Na(+)-H+ antiport blocker). In the presence of amiloride, switching from HEPES buffer to HCO3-/CO2 (pHo of both solutions = 7.4) stimulated a pHi recovery towards more alkaline levels. 3. Amiloride-resistant, HCO(3-)-dependent pHi recovery was inhibited by removal of external Na+ (replaced by N-methyl-D-glucamine), whereas removal of external Cl- (replaced by glucuronate, leading to depletion of internal Cl-), removal of external K+, or decreasing external Ca2+ by approximately tenfold had no inhibitory effect. These results suggest that the amiloride-resistant recovery is due to a Na(+)-HCO3- cotransport into the cell. 4. The stilbene derivative DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid, 500 microM) slowed Na(+)-HCO(3-)-dependent pHi recovery. 5. Intracellular pH increased in Cl(-)-free solution and this increase still occurred in Na(+)-free solution indicating that it is not caused via Na(+)-HCO3- symport and is more likely to be due to Cl- efflux in exchange for HCO3- influx on a sarcolemmal Cl(-)-HCO3- exchanger. The lack of any significant pHi recovery from intracellular acidosis in Na(+)-free solution suggests that this exchanger does not contribute to acid-equivalent extrusion. 6. Possible voltage sensitivity and electrogenicity of the co-transport were examined by using the whole-cell patch clamp technique in combination with SNARF-1 recordings of pHi. Stepping the holding potential from -110 to -40 mV did not affect amiloride-resistant pHi recovery from acidosis. Moreover, following an intracellular acid load, the activation of Na(+)-HCO3- co-influx (by switching from HEPES to HCO3-/CO2 buffer) produced no detectable outward current (outward current would be expected if the coupling of HCO3- with Na+ were > 1.0). 7. Intracellular intrinsic buffering power (beta i) was assessed as a function of pHi (beta i computed from the decrease of pHi following reduction of extracellular NH4 Cl in amiloride-containing solution). beta i in the ventricular myocyte increases roughly linearly with a decrease in pHi according the following equation: beta i = -28(pHi) +222.6. 8. Comparison of acid-equivalent efflux via Na(+)-HCO3- symport and Na(+)-H+ antiport showed that, following an intracellular acidosis, the symport accounts for about 40% of total acid efflux, the other 60% being carried by the antiport.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Role of bicarbonate in pH recovery from intracellular acidosis in the guinea-pig ventricular myocyte. 130 69

[31P]- and [1H]nuclear magnetic resonances recorded in an interleaved fashion were used in order to quantify high-energy phosphates, intracellular pH and lactate in cortical brain slices of the guinea-pig superfused in a CO2/HCO3(-)-buffered medium during and after anoxic insults. The volume-averaged intracellular pH and energy status of the preparation following anoxia were determined. In the presence of external Na+, intracellular pH normalized in 3 min and was significantly more alkaline from 10 to 12 min of recovery, but lactate remained elevated for 12 min of reoxygenation following anoxia. The amount of lactate removed was only 40% of the quantity of acid extruded showing operation of H+ neutralizing transmembrane mechanisms other than transport of lactic acid. Amiloride (1 or 2 mM) did not prevent the recovery of intracellular pH, but it blocked the "overshoot" of the alkalinization at 10-12 min of recovery. In a medium containing 70 mM K+, 60 mM Na+ and 0.1 mM Ca2+, the recovery of pH, but not lactate washout, was significantly delayed. Removal of external Na+ caused severe energetic failure, decreases both in oxygen uptake and in N-acetyl aspartate concentration, indicating loss of viable tissue. In Na(+)-free superfusion, lactic acidosis caused a more severe drop in intracellular pH than in the presence of Na+. Complexing of extracellular Ca2+ in the Na(+)-free medium inhibited the acidification by 0.38 pH units during anoxia which is as much as the acidification caused by lactate accumulation in the absence of Na+. In Na(+)-free medium intracellular pH recovered, however, from an anoxic level to a normoxic value in 6 min. Metabolic damage of the slice preparation induced by anoxia in the absence of Na+ was as profound in the presence as in the absence of Ca2+ showing that accumulation of Ca2+ is not the only reason for the damage. It is concluded that recovery of intracellular pH from lactic-acidosis can occur independently of energetic recovery and involves acid extrusion mechanism(s) that is(are) dependent on external Na+ and sensitive to high K+.
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PMID:Recovery of intracellular pH in cortical brain slices following anoxia studied by nuclear magnetic resonance spectroscopy: role of lactate removal, extracellular sodium and sodium/hydrogen exchange. 131 33

1. The influences of lithium dosage, urine flow rate and acute administration of amiloride on the renal handling of lithium in normal conscious dogs were investigated. 2. Lithium was administered in the diet at daily doses of 100 mg or 2 mg of lithium carbonate for the 2 days preceding the investigation. Urine flow rate was altered by water loading with and without arginine vasopressin infusion (5 pg min-1 kg-1). Amiloride was administered as an intravenous bolus (130 micrograms/kg) followed by a continuous infusion (1.22 micrograms h-1 kg-1). 3. Glomerular filtration rate (exogenous creatinine clearance) did not change within series and was not different between series; it averaged 3.27 ml min-1 kg-1. Control levels of fractional lithium excretion (12.4 +/- 1.2%, mean +/- SEM) were not influenced by hydration, hydration plus arginine vasopressin administration or the lithium dosage. However, in hydrated dogs having a plasma lithium concentration of 130-140 mumol/l, amiloride administration was associated with a 5% increase in fractional lithium excretion (P less than or equal to 0.01). 4. It is concluded that distal tubular lithium reabsorption may take place in sodium-replete conscious dogs undergoing water diuresis. The low fractional lithium excretion even during amiloride infusion (14.1-16.8%) may well be due to a high fractional reabsorption of lithium in the proximal tubules; however, a significant reabsorption of lithium distal to the proximal straight tubules by amiloride-insensitive pathways cannot be excluded.
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PMID:Lithium clearance in dogs: effects of water loading, amiloride and lithium dosage. 132 May 43

The technique for the simultaneous recording of cell volume changes and pHi in single cells was used to study the role of HCO3- in regulatory volume decrease (RVD) by the osteosarcoma cells UMR-106-01. In the presence of HCO3-, steady state pHi is regulated by Na+/H+ exchange, Na+ (HCO3-)3 cotransport and Na(+)-independent Cl-/HCO3- exchange. Following swelling in hypotonic medium, pHi was reduced from 7.16 +/- 0.02 to 6.48 +/- 0.02 within 3.4 +/- 0.28 min. During this period of time, the cells performed RVD until cell volume was decreased by 31 +/- 5% beyond that of control cells (RVD overshoot). Subsequently, while the cells were still in hypotonic medium, pHi slowly increased from 6.48 +/- 0.02 to 6.75 +/- 0.02. This increase in pHi coincided with an increase in cell volume back to normal (recovery from RVD overshoot or hypotonic regulatory volume increase (RVI)). The same profound changes in cell volume and pHi after cell swelling were observed in the complete absence of Cl- or Na+, providing HCO3- was present. On the other hand, depolarizing the cells by increasing external K+ or by inhibition of K+ channels with quinidine, Ba2+ or tetraethylammonium prevented the changes in pHi and RVD. These findings suggest that in the presence of HCO3-, RVD in UMR-106-01 cells is largely mediated by the conductive efflux of K+ and HCO3-. Removal of external Na+ but not Cl- prevented the hypotonic RVI that occurred after the overshoot in RVD. Amiloride had no effect, whereas pretreatment with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) strongly inhibited hypotonic RVI. Thus, hypotonic RVI is mediated by a Na+(out)-dependent, Cl(-)-independent and DIDS-inhibitable mechanism, which is indicative of a Na+(HCO3-)3 cotransporter. This is the first evidence for the involvement of this transporter in cell volume regulation. The present results also stress the power of the new technique used in delineating complicated cell volume regulatory mechanisms in attached single cells.
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PMID:Regulatory volume decrease in the presence of HCO3- by single osteosarcoma cells UMR-106-01. 132 45

1. Active Cl- currents were studied in short-circuited toad skin epithelium in which the passive voltage-activated Cl- current is zero. Under visual control double-barrelled microelectrodes were used for impaling principal cells from the serosal side, or for measuring the pH profile in the solution bathing the apical border. 2. The net inward (active) 36Cl- flux of 27 +/- 8 pmol s-1 cm-2 (16) (mean +/- S.E.M (number of observation)) was abolished by 2 mM-CN- (6.3 +/- 3.5 pmol s-1 cm-2 (8)). The active flux was maintained in the absence of active Na+ transport when the latter was eliminated by either 100 microM-mucosal amiloride, replacement of mucosal Na+ with K+, or by 3 mM-serosal ouabain. 3. In Ringer solution buffered by 24 mM-HCO3- -5% CO2 mucosal amiloride reversed the short circuit current (ISC). The outward ISC was maintained when gluconate replaced mucosal Cl-, and it was reversibly reduced in CO2-free 5 mM-Tris-buffered Ringer solution (pH = 7.40) or by the proton pump inhibitor oligomycin. These observations indicate that the source of the outward ISC is an apical proton pump. 4. Amiloride caused principal cells to hyperpolarize from a basolateral membrane potential, Vb, of -73 +/- 3 (22) to -93 +/- 1 mV (26), and superfusion with CO2-free Tris-buffered Ringer solution induced a further hyperpolarization (Vb = -101 +/- 1 mV (26)) which could be blocked by Ba2+. The CO2-sensitive current changes were null at Vb = EK (potassium reversal potential, -106 +/- 2 mV (55)) implying that they are carried by K+ channels in the basolateral membrane. Such a response cannot account for the inhibition of the outward ISC which by default seems to be located to mitochondria-rich (MR) cells. 5. In the absence of mucosal Cl- a pH gradient was built up above MR cells with pH = 7.02 +/- 0.04 (42) and pH increasing to 7.37 +/- 0.02 (10) above principal cells (pH = 7.40 in bulk solution buffered by 0.1 mM-Tris). This observation localizes a proton pump to the apical membrane of MR cells. Using the integrated diffusion equation it was shown that the measured external pH gradient would account within an order of magnitude for measured currents. 6. Standing gradients of protons were eliminated in the presence of mucosal Cl- suggesting that active uptake of Cl- is associated with the exit of base equivalents across the apical membrane of MR cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Role of proton pump of mitochondria-rich cells for active transport of chloride ions in toad skin epithelium. 133 23

Intracellular pH (pHi) of bovine tissue-cultured corneal endothelial cells has been measured under several experimental conditions. Determinations were made on individual cells using video-imaging techniques that allowed assessment of 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein fluorescence at 440 and 490 nm. Each experiment had a calibration performed on a cell monolayer: this was performed using a high K(+)-nigericin solution. Resting pHi was 7.25 +/- 0.03 (n = 18) in bicarbonate solution at pH 7.4. Amiloride (1 mM) caused an acidification of approximately 0.2 U within 2 min: replacement with normal Ringer allowed a return to normal pHi after an alkali overshoot. Exposure to 20 mM NH4Cl caused alkalinization that became acidic upon washout of NH4Cl. In Na(+)-rich solution pHi returned to normal after acidification but pHi remained low in Na(+)-free solution until substituted by Na(+)-rich solution. Removal of HCO3- from the bathing solution caused a nonsignificant acidification of pHi by 0.1 U at 2 and 4 min, and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 1 mM) acidified pHi by 0.14 U at 2 min and 0.24 U at 4 min. Addition of DIDS (1 mM) in a HCO3(-)-free solution had no effect on pHi. Hydrogen peroxide acidified pHi by 0.3 U at 50 microM and 1 mM. These results indicate that a Na+:H+ antiport exists that regulates pHi even at normal ambient pH in the presence of bicarbonate: this process becomes highly activated after an acid load. There is a DIDS-sensitive HCO3- movement that is probably coupled to Na+ or Cl-.
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PMID:Intracellular pH of tissue-cultured bovine corneal endothelial cells. 133 64


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