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)

Ursodeoxycholate (UDC)-induced HCO3- -rich choleresis may be due to activation of sinusoidal Na+-H+ exchange followed by an increase in intracellular pH (pHi) and HCO3- excretion via canalicular Cl- -HCO3- exchange. To test this hypothesis, we studied the effect of UDC and tauroursodeoxycholate (TUDC) on net H+ efflux from perfused rat livers and pHi in isolated hepatocytes in the presence and absence of amiloride. UDC-induced increases in biliary HCO3- concentration and excretion were inhibited by amiloride. However, these increases were temporally associated with an initial decline in H+ efflux and pHi followed by a gradual recovery toward base line. The initial decline in H+ efflux was associated with a rapid uptake of UDC. Amiloride inhibited only the recovery phases of H+ efflux and pHi. TUDC increased amiloride-sensitive H+ efflux without affecting biliary [HCO3-] and decreased pHi in the presence but not in the absence of amiloride. Amiloride decreased TUDC-induced choleresis and HCO3- excretion most likely by decreasing TUDC excretion. TUDC decreased biliary [Cl-] and increased hepatic O2 uptake more than UDC. We conclude that a rapid influx of UDC in the protonated form decreases pHi and net H+ efflux initially. The recovery phase is due to Na+-H+ exchange activated by decreased pHi and possibly by UDC and increased cellular respiration. TUDC indirectly stimulates Na+-H+ exchange most likely by increasing cellular respiration. UDC-induced HCO3- -rich choleresis, which is observed at a time when both net H+ efflux and pHi are less than control values, is unlikely to be due to a direct activation of Na+-H+ exchange.
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PMID:Ursodeoxycholate-induced changes in hepatic Na+-H+ exchange and biliary HCO3- excretion. 255 Nov 81

The regulation of proton transport and cytosolic pH was studied in rat papillary collecting duct (PCD) cells in culture using a pH-sensitive fluorescence probe, 2,7-bis-carboxyethyl-5,6-carboxyfluorescein (BCECF). Data were obtained from confluent monolayers grown on glass coverslips and dipped in a HCO3- -free medium, pH 7.40. The resting intracellular pH (pHi) was 7.16 +/- 0.03 (n = 20). When PCD cells had been acidified by pretreatment with NH4Cl, pHi immediately recovered toward the resting value. Two mechanisms participated in this recovery: a Na+-dependent mechanism which could be inhibited by amiloride (indicative of Na+-H+ exchanger) and a Na+-independent process (a proton ATPase). The pHi recovery from acid loading was inhibited by amiloride to about 55% of the control recovery (half-maximal effect at 100 microM). The rate of pHi recovery after the readdition of Na+ to a sodium-free medium exhibited saturation kinetics (half maximal rate at 28 mM). Dicyclohexylcarbodiimide (DCCD), an inhibitor of a plasma membrane proton ATPase, and the depletion of cellular ATP induced by 2 mM potassium cyanide (KCN) also partially inhibited the rate of pHi recovery after cell acidification with a NH4Cl load. When PCD cells were treated with 1 mM DCCD, amiloride almost completely inhibited pHi recovery. Amiloride and the removal of external Na+ had induced a gradual fall in pHi to a new resting value and rapidly recovered when Na+ was added. We conclude that PCD cells grown in culture have at least two proton transport mechanisms: a Na+-H+ exchanger and a plasma membrane proton ATPase. The kinetics of these processes can be reliably assessed by the pH-sensitive fluorescent probe, BCECF. Both the Na+-H+ exchanger and the plasma membrane proton ATPase may contribute to urinary acidification.
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PMID:Dual regulatory mechanisms of proton transport in rat papillary collecting duct cells in culture. 255 3

Addition of EGF to human epidermoid carcinoma A431 cells increases the rate of fluid-phase pinocytosis 6-10-fold as measured by horseradish peroxidase uptake (Haigler, H.T., J. A. McKanna, and S. Cohen. 1979. J. Cell Biol. 83:82-90). We show here that in the absence of extracellular Na+ or in the presence of amiloride the stimulation of pinocytosis by EGF is substantially reduced. Amiloride had no effect on the endocytosis of EGF itself or of transferrin, demonstrating that the receptor-mediated endocytotic pathway operated normally under conditions that blocked stimulated pinocytosis. Amiloride blocked EGF-stimulated pinocytosis in both HCO3(-)-containing and HCO3(-)-free media. The EGF-stimulated pinocytotic activity can frequently be localized to areas of the cell where membrane spreading and ruffling are taking place. These results demonstrate that (a) EGF induces a distinct amiloride-sensitive endocytotic pathway on A431 cells; (b) occupied EGF receptors do not utilize this pathway for their own entry; (c) endocytosis of occupied EGF receptors is not in itself sufficient to stimulate pinocytosis.
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PMID:Distinct endocytotic pathways in epidermal growth factor-stimulated human carcinoma A431 cells. 255 6

The present studies were designed to test our previous suggestion that Na+/H+ exchange was activated by muscarinic stimulation of rat parotid acinar cells. Consistent with this hypothesis, we demonstrate here that intact rat parotid acini stimulated with the muscarinic agonist carbachol in HCO3- -free medium show an enhanced recovery from an acute acid load as compared to similarly challenged untreated preparations. Amiloride-sensitive 22Na uptake, due to Na+/H+ exchange, was also studied in plasma membrane vesicles prepared from rat parotid acini pretreated with carbachol. This uptake was stimulated two-fold relative to that observed in vesicles from control (untreated) acini. This stimulation was time dependent, requiring approximately 15 min of acinar incubation with carbachol to reach completion, and was blocked by the presence of the muscarinic antagonist atropine (2 x 10(-5) M) in the pretreatment medium. The effect of carbachol was dose dependent with K0.5 approximately 3 x 10(-6) M. Stimulation of the exchanger was also seen in vesicles prepared from acini pretreated with the alpha-adrenergic agonist epinephrine, but not with the beta-adrenergic agonist isoproterenol, or with substance P. Kinetic analysis indicated that the stimulation induced by carbachol was due to an alkaline shift in the pH responsiveness of the exchanger in addition to an increased apparent transport capacity. Taken together with previous results from this and other laboratories, these results strongly suggest that the Na+/H+ exchanger and its regulation are intimately involved in the fluid-secretory response of the rat parotid.
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PMID:Agonist-induced activation of Na+/H+ exchange in rat parotid acinar cells. 255 3

In isolated perfused rabbit mandibular glands undergoing stimulation with 0.8 microM acetylcholine, replacement of HCO3- with acetate (25 mM) increased fluid secretion by more than 100%. Other short-chain fatty acids, except for propionate, had a similar effect. We focused our further studies on acetate, and in order to find out the cause of its stimulatory effect we investigated whether acetate itself was transported. In the absence of any other transportable anions 25 mM acetate supported secretion at the same rate as 25 mM HCO3- or 25 mM Cl-, i.e. 20% of the control rate. In solutions containing acetate as the only major anion (146 mM), fluid secretion was maintained at about 50% of the control rate. Amiloride (1 mM) inhibited this secretion by about 90%. In glands perfused with acetate/Cl- solutions, when the stimulatory effect was normally observed, amiloride (1 mM) inhibited secretion by 50-60% and SITS (0.1 mM) had no effect. Probenecid reversibly inhibited 75% of secretion in these glands, but it also inhibited 92% of secretion in glands perfused without any acetate. Interestingly, the acetate effect was abolished in glands stimulated with a higher concentration of acetylcholine (80 microM). Results of this study suggest that acetate can be transported by salivary endpieces and that this transport involves an amiloride-sensitive Na+-H+ antiport. We postulate that acetate may in addition have some regulatory or modifier role in salivary secretion.
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PMID:Acetate stimulates secretion in the rabbit mandibular gland. 272 37

Porcine gallbladder, stripped of serosal muscle, mounted in Ussing chambers, and bathed in plasma-like Ringer solution generates a serosal positive transepithelial potential of 4-7 mV and a short-circuit current (Isc) of 50-120 microA/cm2. Substitution of Cl with gluconate or HCO3 with N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) results in a 50% decrease in Isc. Treatment with 1 mM amiloride (mucosal side) or 0.1 mM acetazolamide (both sides) causes 25-27% inhibition of the Isc. Mucosal addition of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid inhibits the Isc by 17%. Serosal addition of 0.1 mM bumetanide inhibits the Isc by 28%. Amiloride (1 mM) inhibits the net transepithelial fluxes of Na and Cl by 55 and 41%, respectively. Substitution of Cl with gluconate inhibits the net Na flux by 50%, whereas substitution of HCO3 with HEPES inhibits 85-90% of the net Na flux and changes Cl absorption to net secretion. Based on these results, it is hypothesized that Na and Cl transport across the apical membrane is mediated by two pathways, Na-H/Cl-HCO3 exchange and Na-HCO3 cotransport. Partial recycling of Cl and HCO3 presumably occurs through a Cl conductive pathway and Cl-HCO3 exchange, respectively, in the apical membrane. This results in net Na absorption, which accounts for most of the Isc observed under basal conditions. The effect of bumetanide on the basolateral membrane and the fact that Cl secretion occurs when HCO3 is absent suggests that Cl secretion involves a basolateral NaCl or Na-K-Cl cotransport system arranged in series with a Cl conductive pathway in the apical membrane.
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PMID:Sodium and chloride transport across the isolated porcine gallbladder. 275 Aug 90

We used an in vitro model, MDCK cyst, to determine the extent to which pharmacologic compounds known to inhibit plasma membrane solute transport mechanisms could alter the enlargement of renal epithelial cysts. Solitary MDCK cells cultured within collagen gel undergo clonal growth to form true epithelial cysts in which a single layer of polarized cells (apex toward lumen) encloses a fluid-filled cavity. Repeated observations by light microscopy were used to quantitate the rate of cyst growth in diameter, and demonstrated that cyst enlargement involved an increase in cell number (proliferation) and a net increase in intracystic volume (fluid secretion). Intracyst pressure was greater than the interstitium (6.7 mm H2O +/- 3.1 SD), indicating that fluid entry was secondary to net solute accumulation. Amiloride and seven amiloride analogs that inhibited to different degrees conductive Na+ transport, Na+-dependent H+ transport and Na+-dependent Ca++ transport reversibly decreased the rate of cyst enlargement. The effectiveness of these agents to retard cyst enlargement correlated with their relative potencies to inhibit Na+-dependent Ca++ transport. Morphologic examination indicated that amiloride and amiloride analogs decreased cell proliferation and fluid secretion to the same degree. Ouabain and vanadate (Na+K,ATPase inhibitors), and L-645,695 (Na+-dependent Cl-/HCO3- inhibitor) potently slowed cyst expansion. In contrast to amiloride and amiloride analogs, these agents caused an unusual degree of cellular stratification within the cyst walls, a finding consistent with the notion that fluid secretion was inhibited to a greater extent then cellular proliferation. We conclude that chemical inhibitors of primary and secondary active solute transport can diminish or halt the enlargement of epithelial cysts in vitro by decreasing the rate of cellular proliferation and/or net fluid secretion.
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PMID:Chemical modification of cell proliferation and fluid secretion in renal cysts. 277 Jan 16

Chronic hypercapnia is associated with increased proximal HCO3 reabsorption that is thought to be mediated by a Na-H antiporter. We hypothesized that chronic hypercapnia would be associated either with increased Vmax or with decreased Km of the Na-H antiporter. To test this hypothesis we made rabbits hypercapnic for 48 h by exposure to 10% CO2. In both control and hypercapnic animals, cortical luminal membranes were enriched over the homogenate 16-fold in alkaline phosphatase and 10-fold in maltase activity. The kinetic activity of the Na-H antiporter was measured by the dissipation of the quenching of acridine orange by addition of different Na concentrations. Chronic hypercapnic rabbits had significantly higher Vmax of the Na-H antiporter of luminal membranes than controls (593 +/- 81 vs. 252 +/- 40 arbitrary fluorescence units X min-1 X 300 micrograms protein-1, P less than 0.01). The Km, however, was not different between control and hypercapnic rabbits. 22Na uptake in presence of an outwardly directed pH gradient was significantly higher in vesicles from hypercapnic rabbits than controls. Amiloride inhibited the Na-H antiporter (as assessed by acridine orange quenching or 22Na uptake) to the same degree in membranes from both control and hypercapnic rabbits, suggesting that the increase in Vmax is mediated by the electroneutral component of the Na-H antiporter. In addition, under voltage clamp conditions by K and valinomycin the Vmax was still increased in membranes from hypercapnic animals, again suggesting that the increase in Vmax is mediated by the electroneutral component of the Na-H antiporter. The uptake of D-[3H]glucose by luminal membranes was not different between control and hypercapnic rabbits, indicating a specific enhancement of the Na-H antiporter. Acute hypercapnia (4 h) failed to increase the Vmax of the Na-H antiporter despite comparable increase in PCO2. Thus chronic hypercapnia, but not acute hypercapnia, induces a selective and specific increase in the Vmax of Na-H antiporter, and this may mediate the adaptation to chronic hypercapnia.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Chronic hypercapnia enhances Vmax of Na-H antiporter of renal brush-border membranes. 282 Feb 41

1. Double-barrelled, neutral-carrier pH-sensitive micro-electrodes were used to measure the intracellular pH (pHi) and the pHi regulation of neuropile glial (n.g.) cells and of identified neurones of the leech Hirudo medicinalis. 2. The distribution of H+ in the n.g. cells and in the neurones was found not to be in electrical equilibrium. The mean pHi of the n.g. cells was 6.87 +/- 0.13 (mean +/- S.D. of mean here and for all following data n = 27) in HEPES-buffered leech saline (pHo = 7.4) and 7.18 +/- 0.19 (n = 13) in 2% CO2-11 mM-HCO3(-)-saline. The mean pHi was 7.28 +/- 0.1 (n = 20) in Retzius neurones and 7.32 +/- 0.15 (n = 12) in noxious neurones in HEPES-buffered leech saline, and 7.20 +/- 0.15 (n = 10) and 7.27 +/- 0.16 (n = 6) in 2% CO2-11 mM-HCO3(-)-buffered saline in these two types of neurones, respectively. 3. The cytoplasmic buffering power, as calculated by the change in pHi following the change from 2% CO2-11 mM-HCO3- to 5% CO2-22 mM-HCO3- in the leech saline, was 20-30 mM/pH unit in the n.g. cells and between 12 and 33 mM/pH unit in the neurones. 4. The recovery of pHi in n.g. cells from an experimentally induced acidification (addition and removal of 20 mM-NH4Cl) was dependent on the presence of external Na+. Independent of the buffer system used, pHi recovery was inhibited when external Na+ was exchanged by N-methyl-D-glucamine. Amiloride (2-3 mM) reduced the rate of pHi recovery by about 50% in these n.g. cells. 5. In CO2-HCO3(-)-free saline, or in the presence of the anion exchange blocker 4-acetamido-4'-isothiocyanostilbene-2, 2'-disulphonic acid (SITS, 0.5 mM), pHi recovery from an acid load was often slowed by up to 50% in n.g. cells. This suggests that there is a significant contribution of a HCO3(-)-dependent membrane transport to pHi regulation in n.g. cells. 6. When a HEPES-buffered saline was exchanged by a 2% CO2-11 mM-HCO3(-)-buffered saline, the pHi of n.g. cells increased by 0.31 pH units. This alkaline shift was reversible upon removal of the CO2-HCO3- and was absent in the Na+-free saline. It was not inhibited by 1 mM-furosemide or by 0.5 mM-SITS.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The regulation of intracellular pH by identified glial cells and neurones in the central nervous system of the leech. 282 Dec 43

Posthypercapnic metabolic alkalosis has been attributed to decreased HCO3 excretion because of low glomerular filtration rate (GFR), volume contraction, or chloride depletion. We have previously shown that chronic hypercapnia enhances the Vmax of the Na+-H+ antiporter. We reasoned that an increased Vmax of the Na+-H+ antiporter could play a role in the maintenance of posthypercapnic metabolic alkalosis. To test this hypothesis, we measured the kinetics of the Na+-H+ antiporter by the dissipation of the quenching of acridine orange fluorescence in purified brush-border membrane obtained from posthypercapnic rabbits. The kinetic parameters were measured in controls and in rabbits that were exposed to hypercapnia for 48 h and then allowed to breathe room air for 3, 24, or 48 h. In luminal membranes prepared from posthypercapnic animals, the Vmax of the Na+-H+ antiporter was significantly increased after 3 and 24 h but not after 48 h compared with controls. The increase in Vmax was not different from that of hypercapnic animals. There was no difference in the Km of the Na+-H+ antiporter among these five groups. Amiloride inhibited the Vmax equally in membranes from control and posthypercapnic rabbits. Proton permeability was comparable among the groups. These data indicate that the increase in Vmax in posthypercapnic rabbits is mediated through the electroneutral Na+-H+ exchange and not through conductive H+ and Na+ pathway. Glucose uptake was not different in control and posthypercapnia, indicating a selective increase in Na+-H+ antiporter activity. At 3 and 24 h posthypercapnia, HCO3 concentration was higher than control.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Na+-H+ antiporter in posthypercapnic state. 282 35


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