Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the present in-vitro study we investigated the possible role of the calmodulin-antagonistic drugs loperamide and calmidazolium in the regulation of transepithelial Ca2+ transport of human duodenum. Brush border membrane vesicles and basolateral membrane vesicles were simultaneously prepared from surgically resected pieces of morphologically intact human duodenum with a modified Percoll-gradient centrifugation method. Brush border and basolateral membrane vesicles were characterized using enzyme marker analysis and electron microscopy: alkaline phosphatase was enriched 20-fold in brush border membrane vesicles, whereas [Na+ + K+]-stimulated adenosine triphosphatase was enriched 15-fold in basolateral membrane vesicles. Calmodulin activity was determined by a specific radioimmunoassay after solubilizing brush border and basolateral membrane vesicles in 1% Triton X-100. In basolateral membrane vesicles, we found no calmodulin activity. In brush border membrane vesicles calmodulin activity was impaired by 50% after pre-incubation with loperamide or calmidazolium. We measured calcium, sodium, D-glucose and D-mannitol uptake with a rapid filtration technique. Before the transport experiments, brush border and basolateral membrane vesicles were pre-incubated with 5 microM loperamide or 5 microM calmidazolium for 60 min at 5 degrees C. In drug-pretreated, brush border membrane vesicles calcium uptake was significantly reduced after 1 min incubation (-25% +/- 5%, P less than 0.05); this effect was completely reversed in the presence of 5 microM calmodulin. In basolateral membrane vesicles, we found two Ca2+ transport systems: (1) Na+/Ca2+ exchange and (2) ATP-dependent Ca2+ transport. In basolateral membrane vesicles loperamide had no effect. Calmidazolium had no effect on Na+/Ca2+ exchange, but significantly inhibited ATP-dependent Ca2+ transport. This effect could not be reversed by calmodulin.
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PMID:Effect of two potent calmodulin antagonists on calcium transport of brush border and basolateral vesicles from human duodenum. 297 85

Transport of D-glucose, p-aminohippurate and tetraethylammonium has been studied using renal brush border membrane vesicles isolated from rats with uranyl nitrate-induced acute renal failure (ARF). Initial rate and overshoot magnitude of Na+ gradient-dependent D-glucose uptake were decreased in brush border membrane vesicles from ARF rats compared with normal rats, although there was no significant difference on D-glucose uptake in the presence of equilibrated Na+ between normal and ARF rats. Uptake of p-aminohippurate by membrane vesicles from ARF rats did not differ from normal membrane vesicles. Uptake of tetraethylammonium with or without an H+ gradient was decreased in membrane vesicles from ARF rats compared with normal rats. Dissipation rate of H+ gradient across brush border membranes did not differ between both groups. In vitro incubation of normal brush border membrane vesicles with uranyl nitrate caused no alteration in any substrate transport. However, enzyme activities such as (Na+ + K+)-adenosine triphosphatase in renal cortical homogenate were inhibited markedly in the presence of uranyl nitrate. These results suggest that uranyl nitrate-induced ARF caused alterations in the transport properties of renal brush border membranes and that these transport dysfunctions were not due to the direct effect of uranyl nitrate, but could be secondarily induced after the impairment of the integrity for tubular cells.
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PMID:Transport of p-aminohippurate, tetraethylammonium and D-glucose in renal brush border membranes from rats with acute renal failure. 298 96

Purified brush border membranes were obtained from homogenized jejunal epithelial cells of cattle by divalent cation aggregation of nonbrush border membranes and differential centrifugation. Membrane marker enzyme assays determined effectiveness of the fractionation procedure. Compared with cellular homogenate, maltase and sodium+-potassium+-adenosine triphosphatase specific activities in the membrane fraction isolated from the interface of discontinuous (35 and 45% wt/wt) sucrose gradients increased 14.5- and 1.9-fold whereas enzyme recoveries averaged 20.2 and 2.4%. These data indicate significant enrichment in brush border membranes with minimal basolateral membrane contamination. Vesicles formed from this membrane fraction had a predominately (93%) luminal side out orientation. After incubating vesicles with radiolabeled substrates, vesicles and accumulated substrates were separated from the incubation buffer by filtration and substrate uptake quantified by liquid scintillation counting. Observed uptake was the result of substrate accumulation within an osmotically active intravesicular space and was not due to nonspecific binding of the substrate to vesicular membranes. Vesicles exhibited sodium-dependent and independent substrate uptake pathways and were able to discriminate between substrate stereoisomers for uptake. Major differences were not detected between results obtained with vesicles prepared from fresh or frozen intestines. These vesicles can be utilized to investigate nutrient uptake by the bovine small intestine.
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PMID:Preparation of brush border membrane vesicles from fresh and frozen bovine intestine for nutrient uptake studies. 300 74

(Na+ + K+)-activated adenosine triphosphatase activity in the mucosal homogenate of rat small intestine estimated under conditions of experimental diabetes, application of corticosteroids, adrenalectomy or inhibition of adrenocortical function suggests a general parallelism between the capacity for monosaccharide absorption and enzyme activity. Studying the kinetic parameters it has been found that the maximal velocities of monosaccharide uptake as well as of (Na+ + K+)-activated adenosine triphosphatase reaction are significantly different, whereas sugar concentrations for halfmaximal transport velocities and enzyme-substrate affinity constants remain unaltered. From studies with purified brush borders and basolateral plasma membranes it has been shown that the activity changes were caused exclusively by that part of (Na+ + K+)-activated adenosine triphosphatase which is localized in the basolateral plasma membranes. The enzyme activity in the brush border region remains unchanged. These findings support a concept of intestinal transport mechanism which suggests that the basolateral part of (Na+ + K+)-activated adenosine triphosphatase is responsible for metabolic energy supply.
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PMID:Effect of diabetes and adrenocortical state on intestinal transport capacity and (Na+ + K+)-activated adenosine triphosphatase activity. 302 48

Quinidine is known to inhibit the renal clearance of digoxin without affecting glomerular filtration rate. The renal interaction between these drugs was investigated by a combination of in vivo and in vitro methods. The uptake of digoxin by brush border membrane vesicles was not affected by quinidine. Similarly, digoxin did not inhibit the uptake of the cation N-methylnicotinamide by these vesicles and did not alter the binding kinetics of digoxin to the Na+, K+-adenosine triphosphatase by the antiluminal membrane vesicles. By using the in vivo multiple indicator dilution technique transtubular transport of digoxin was documented; renal-artery infusion of quinidine did not affect the recovery of digoxin in the renal vein or urine. Clearance studies documented that the decrease in the renal clearance of digoxin is paralleled by a significant fall in renal blood flow evidenced by a decrease in p-aminohippuric acid clearance. It is concluded that quinidine inhibits the renal excretion of digoxin not by competition at the tubular cell membrane level, but rather by decreasing renal blood flow. A parallel decrease in biliary clearance of digoxin is documented and may suggest a similar mechanism.
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PMID:Effects of quinidine on the renal tubular and biliary transport of digoxin: in vivo and in vitro studies in the dog. 320 14

Brush border vesicles were isolated from surgically resected pieces of human jejunum and ileum using a Mg2+/EGTA precipitation method. When compared to the homogenate, the final membrane preparation contained alkaline phosphatase at a 14 times higher concentration and almost no (Na++K+)-stimulated adenosine triphosphatase. An Na+/H+ antiport could be demonstrated in the jejunum by imposing a pH gradient between the interior and the outside of the vesicles (pHinside 5.2, pHoutside 7.2). In the presence of amiloride or harmaline, Na+/H+ antiport was inhibited by 60 +/- 5% (p less than 0.05) or 65 +/- 5% (p less than 0.05), respectively. In vesicles of human ileum we found an Na+/H+ antiport and in contrast to the jejunum a Cl-/OH- antiport could be demonstrated by imposing a pH gradient (pHinside 5.2, pHoutside 7.2). Besides this double-exchange mechanism for sodium and chloride, a Na+/Cl- cotransport and a Cl- conductive pathway could be detected in ileal brush border vesicles. In the presence of the anion transport inhibitors, furosemide, SITS and DIDS activities of Cl-/OH- antiport and Na+/Cl- cotransport were suppressed by 30 +/- 5% (p less than 0.05), 35 +/- 5% (p less than 0.05) and 40 +/- 5% (p less than 0.05), respectively. We conclude that absorption of sodium and chloride in the absence of organic solutes is mediated through different transport mechanisms at the luminal plasma membrane, which are in part subject to regulation by sodium and chloride transport inhibitors.
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PMID:Effect of inhibitors on sodium and chloride transport in brush border vesicles from human jejunum and ileum. 367 37

The virus of transmissible gastroenteritis produced sprue-like lesions in the small intestines of young pigs. These lesions were characterized by villous shortening, fusing and blunting in the jejunum and ileum. There was decreased height of the brush border and morphologic alteration of the villous epithelial cells from simple columnar to a variable cuboidal type. Accompanying these microscopic lesions were histochemical changes characterized by decreased staining intensity of acid phosphatase, alkaline phosphatase, adenosine triphosphatase, leucine aminopeptidase, succinic dehydrogenase and malic dehydrogenase in the affected intestinal mucosa. The clinical nature of transmissible gastroenteritis in the pig together with the histopathologic and histochemical changes may provide a useful experimental model for obtaining additional basic information on enteric disturbances.
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PMID:Experimental sprue-like small intestinal lesions in pigs. 422 30

Endogenous enzyme activity can be readily and routinely demonstrated in ultrathin, frozen sections for electron microscopy. The procedure employed to obtain the best structural preservation as well as enzyme activity in thin sections involved fixation in glutaraldehyde, embedding in thiolated gelatin or pure gelatin, partial dehydration in glycerol, and sectioning in a cryostat at -35 degrees C with a slightly modified Porter-Blum microtome on which the tissue is maintained at -70 degrees C and the knife at -23 degrees C. Kidney cortex was used as test tissue, but a few other organs were occasionally used. Thin sections were floated on the surface of several incubation media routinely employed for enzyme cytochemistry. Positive, specific reactions were obtained for alkaline phosphatase in kidney brush border, for adenosine triphosphatase in brush border and in basal membranes of distal tubules, for acid phosphatase and esterase in lysosomes, and for NADH diaphorase in mitochondria. Mitochondrial ATPase was sporadically evident only in the distal tubule of the kidney. Localizations of enzyme activity reported by other technical approaches were confirmed and in some cases somewhat improved.
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PMID:Ultrathin frozen sections. II. Demonstration of enzymic activity. 429 6

Inhibition of renal Na+,K+-adenosine triphosphatase is an early biochemical manifestation of gentamicin treatment in rats. Studies with isolated, perfused rat kidneys in filtering and nonfiltering modes indicate that gentamicin is transported across the brush border membrane before enzyme inhibition. The drug caused enzyme inhibition (42%) only in filtering kidneys, and this inhibition was blocked by spermine, an inhibitor of gentamicin binding. In purified rat renal basolateral membranes, bound [3H]gentamicin was displaced 88% by unlabeled gentamicin. After in vivo exposure to [3H]gentamicin, the radioactivity associated with the isolated basolateral membranes was displaced only 46% by unlabeled drug. These results suggest that inhibition of renal Na+,K+-adenosine triphosphatase by gentamicin is probably due to an interaction at the cytoplasmic face of the basolateral membrane. Scatchard plots of [3H]gentamicin binding to basolateral and brush border membranes revealed a single class of noninteracting sites in each membrane. Gentamicin did not change the bulk membrane lipid fluidity, as estimated by the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene.
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PMID:Inhibition of renal Na+, K+-adenosine triphosphatase by gentamicin. 609 9

Pyrophosphate, p-nitrophenyl phosphate and a variety of pyrimidine and purine nucleotides are hydrolyzed by the solubilized membrane-bound enzymes of the brush border plasma membrane of Hymenolepis diminuta. The pH optima (or ranges) for hydrolysis of substrates are 8.0 (pyrophosphate), 8.8 (p-nitrophenyl phosphate), 8.4-8.9 (nucleoside monophosphates), and 7.1-8.1 (nucleoside triphosphates); all substrates, with the exception of nucleoside triphosphates, have a higher affinity for the solubilized enzyme at pH 7.4 than at their optimal pH for hydrolysis. ATP is degraded completely by the enzyme preparation to adenosine and inorganic phosphate, but since neither ADP nor ATP accumulate in the incubation medium it is not known whether ATP hydrolysis involves the sequential hydrolysis of terminal phosphate groups. Isoelectric focusing and various chromatographic procedures (gel permeation, ion-exchange and hydrophobic interaction chromatography) fail to separate the alkaline phosphatase, phosphodiesterase, 5'-nucleotidase, adenosine triphosphatase and ribonuclease activities associated with the solubilized membrane preparation. Additionally, inhibitor studies indicate that only a single enzyme with low substrate specificity is involved in the hydrolysis of nucleotides, p-nitrophenyl phosphate, pyrophosphate and hexose phosphate esters. Purines and pyrimidines and their nucleosides interact with the active site, and in some instances activity of the enzyme is stimulated by an unknown mechanism.
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PMID:Nucleotide hydrolysis by solubilized membrane-bound enzymes of the brush border plasma membrane of Hymenolepis diminuta. 613 88


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