Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two populations of intercalated cells, type A and type B, are present in the rat cortical collecting duct (CCD). Type A cells are involved in proton secretion and contain an apical H(+)-adenosinetriphosphatase (ATPase) and a basolateral Cl(-)-HCO3- exchanger. Type B cells are believed to be involved in HCO3- secretion, which is mediated by a Cl(-)-HCO3- exchange process and is Cl- dependent. The aim of this study was to examine the morphological and immunocytochemical response of type B intercalated cells in the rat to increased delivery of Cl- to the CCD. This was accomplished by chronic infusion of a loop diuretic, bumetanide (30 mg.kg body wt-1.day-1), via an osmotic minipump, and simultaneous administration of 0.9% sodium chloride in the drinking water for 6 days. The kidneys were preserved by in vivo perfusion with a periodate-lysine-paraformaldehyde fixative and processed for horseradish peroxidase and protein A gold immunocytochemistry, using rabbit polyclonal antibodies against carbonic anhydrase II, proton ATPase, and band 3 protein. Chronic infusion of bumetanide in combination with a high salt intake was associated with significant changes in the intercalated cells. Type B cells were increased in size and exhibited numerous apical microvilli, increased basolateral membrane area, and marked cytoplasmic and basolateral labeling for H(+)-ATPase. In contrast, type A cells were small and had sparse apical microprojections. H(+)-ATPase immunolabeling was observed primarily over apical tubulovesicles, and there was decreased basolateral immunolabeling for band 3 protein and occasional labeling for band 3 in lysosome-like structures. These observations support the hypothesis that increased delivery of Cl- to the CCD is associated with stimulation of type B intercalated cells to secrete HCO3-. The observations in type A cells are consistent with the cells being in a resting or inactivated state.
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PMID:Immunocytochemical response of type A and type B intercalated cells to increased sodium chloride delivery. 153 33

We examined the effect of Cl- depletion metabolic alkalosis (CDA) on H(+)-ATPase and band 3 protein localization in intercalated cells (IC) of the rat cortical collecting duct (CCD) and the outer medullary collecting duct (OMCD). After 30 min of peritoneal dialysis against 0.15 M NaHCO3 to produce CDA, or Ringer bicarbonate to serve as controls (CON), both groups were infused intravenously with an 80 mM Cl- solution for 90 min. For CDA vs. CON, physiological parameters were as follows: plasma total CO2, 38.0 +/- 1.1 vs. 27.8 +/- 0.6 meq/l (P less than 0.001); urinary total CO2 excretion, 141 +/- 89 vs. 20 +/- 3 neq.min-1.100 g body wt-1; and urinary Cl- excretion, 20 +/- 10 vs. 486 +/- 144 neq.min-1.100 g body wt-1 (P less than 0.001). H(+)-ATPase was localized in thin sections using a rabbit polyclonal antibody against the 70-kDa subunit of bovine brain H(+)-ATPase. Band 3 protein was localized using a polyclonal antibody against the 43-kDa subunit of the cytoplasmic domain of human erythrocyte band 3 protein. In CON rats, H(+)-ATPase localized along the apical plasma membrane and over the apical cytoplasmic vesicles of type A ICs in the CCD and ICs of the OMCD. H(+)-ATPase was observed along the basolateral plasma membrane and over cytoplasmic vesicles throughout type B ICs. In CDA rats, H(+)-ATPase was only observed over apical cytoplasmic vesicles in type A ICs and in the majority of OMCD ICs. In type B ICs, H(+)-ATPase staining was intensified along the basal plasma membrane in CDA. Band 3 protein was consistently localized in the basolateral plasma membrane of all type A cells in the CCD and ICs of the OMCD in both CON and CDA. In summary, stimulation of HCO3- secretion in rats caused withdrawal of H(+)-ATPase from the apical plasma membrane and storage in apical cytoplasmic vesicles of ICs of the OMCD and type A ICs of the CCD. H(+)-ATPase appeared to be inserted into the basal plasma membrane of type B ICs. These findings suggest that, during correction of CDA, proton secretion by type A and OMCD ICs is suppressed and proton transport across the basolateral plasma membrane of type B ICs is stimulated.
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PMID:Response of intercalated cells to chloride depletion metabolic alkalosis. 153 35

The effects of the allosteric ligands UMP, IMP, and ornithine on the partial reactions catalyzed by Escherichia coli carbamyl phosphate synthetase have been examined. Both of these reactions, a HCO3(-)-dependent ATP synthesis reaction and a carbamyl phosphate-dependent ATP synthesis reaction, follow bimolecular ordered sequential kinetic mechanisms. In the ATPase reaction, MgATP binds before HCO3- as established previously for the overall reaction catalyzed by carbamyl phosphate synthetase [Raushel, F. M., Anderson, P. M., & Villafranca, J. J. (1978) Biochemistry 17, 5587-5591]. The initial velocity kinetics for the ATP synthesis reaction indicate that MgADP binds before carbamyl phosphate in an equilibrium ordered mechanism except in the presence of ornithine. Determination of true thermodynamic linked-function parameters describing the impact of allosteric ligands on the binding interactions of the first substrate to bind in an ordered mechanism requires experiments to be performed in which both substrates are varied even if only one is apparently affected by the allosteric ligands. In so doing, we have found that IMP has little effect on the overall reaction of either of these two partial reactions. UMP and ornithine, which have a pronounced effect on the apparent Km for MgATP in the overall reaction, both substantially change the thermodynamic dissociation constant for MgADP from the binary E-MgADP complex, Kia, in the ATP synthesis reaction, with UMP increasing Kia 15-fold and ornithine decreasing Kia by 18-fold. By contrast, only UMP substantially affects the Kia for MgATP in the ATPase reaction, increasing it by 5-fold.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Quantifying the allosteric properties of Escherichia coli carbamyl phosphate synthetase: determination of thermodynamic linked-function parameters in an ordered kinetic mechanism. 153 67

Aminoimidazole riobnucleotide carboxylase, the sixth step in the purine biosynthetic pathway, catalyzes the conversion of aminoimidazole ribonucleotide (AIR) to carboxyaminoimidazole ribonucleotide (CAIR). The gene products of the purE and purK genes (PurE and PurK, respectively) thought to be responsible for this activity have been overexpressed and the proteins purified to homogeneity. PurE separates from PurK in the first ammonium sulfate fractionation during the purification. No evidence for association of the two gene products under a variety of conditions using a variety of methods could be obtained. To facilitate the assay for CAIR production, the purC gene product, 5-aminoimidazole-4-N-succinylcarboxamide ribonucleotide (SAICAR) synthetase has also been overexpressed and purified to homogeneity. The activities of PurE, PurK, and PurE.PurK have been investigated. PurE alone is capable of catalyzing the conversion of AIR to CAIR 1 million times faster than the nonenzymatic rate. The Km for HCO3- in the PurE-dependent reaction is 110 mM! PurK possesses an ATPase activity that is dependent on the presence of AIR. No bicarbonate dependence on this reaction could be demonstrated (less than 100 microM), and AIR is not carboxylated during the hydrolysis of ATP. Incubation of a 1:1 mixture of PurE and PurK at low concentrations of bicarbonate (less than 100 microM) revealed that CAIR is produced but requires the stoichiometric conversion of ATP to ADP and Pi. No dependence on the concentration of HCO3- could be demonstrated. A new energy requirement in the purine biosynthetic pathway has been established.
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PMID:Purification and characterization of the purE, purK, and purC gene products: identification of a previously unrecognized energy requirement in the purine biosynthetic pathway. 153 90

We investigated the regulatory transport processes that maintain intracellular K+ homeostasis in cultured rat glomerular mesangial cells (MCs). Intracellular K+ concentration ([K+]i) of quiescent MCs, passages 3-8, grown to subconfluence on glass cover slips, was assessed by spectrofluorometry using the K(+)-sensitive dye, K(+)-binding benzofuran isophthalate (PBFI). Serum-starved MCs were incubated at 37 degrees C in 5 microM PBFI for 90 min. Excitation ratios of luminescences at 340 and 380 nm, measured at a constant emission at 500 nm, were used to determine [K+]i. Ionophores valinomycin and nigericin were used to clamp [K+]i to known [K+]o and thereby obtain an intracellular calibration of dye. Dependence of fluorescence ratio on [K+]i conformed to Michaelis-Menten behavior, with a Km of 113 mM (n = 40). PBFI retains its sensitivity to alterations in [K+]i with pH change (pHi from 6.5 to 7.5) but is relatively insensitive when intracellular Na+ is greater than 75 mM and cell osmolarity exceeds 500 mM. Normal resting [K+]i for all experiments was determined in MCs to be 102 +/- 7 mM (n = 81) in a HCO3(-)-free HEPES-buffered solution. When MCs were exposed to ouabain, [K+]i fell to 48 +/- 6 mM and did not recover, suggesting presence of Na(+)-K(+)-ATPase. When MCs were exposed to furosemide, [K+]i transiently declined to 58 +/- 11 mM, which was followed by a rapid recovery to near steady state, indicating additional presence of Na(+)-K(+)-Cl- cotransporter. Recovery was completely abolished when MCs were exposed to ouabain.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Regulation of intracellular potassium in mesangial cells: a fluorescence analysis using the dye, PBFI. 155 63

Although trabecular meshwork cells are presumed to play an important role in determining ocular aqueous outflow resistance, little is known about their membrane transport characteristics. As in vivo access by microelectrodes is difficult, we used cell culture techniques to facilitate membrane voltage recording from cultured bovine trabecular meshwork cells. Phase-contrast microscopy revealed the presence of epithelial-like and spindle-shaped cell types. The mean membrane voltage for epithelial cells was -49.7 +/- 0.8 mV (S.E.M., n = 143) and for spindle cells was -70.9 +/- 1.9 mV (S.E.M., n = 48). These cells possess an electrogenic Na+/K(+)-ATPase and a K+ conductance. K transference numbers (tk) for [K+] from 5 to 80 mM were 0.50 for epithelial cells and 0.71 for spindle cells. The epithelial cells lack the electrogenic Na+/HCO3-symport, thereby enabling their differentiation from corneal endothelial cells and confirming previous reports of differences between these cell types. A proportion of spindle cells demonstrated spontaneous and induced fluctuations of membrane voltage. One millimolar Ba2+ (n = 9) induced an immediate depolarization of membrane voltage, with the onset of 'overshooting' action potentials, which were dependent on extracellular Ca2+ and Na+ but were not blocked by tetrodotoxin, 10(-6) M. Spindle cells showed parallel alignment of intracellular smooth muscle specific alpha-isoactin filaments, whereas epithelial cells showed specks of non-fibrous staining. Electron microscopy revealed that epithelial cells had the characteristics of metabolically active cells, with few intermediate filaments (10-12 nm) and microfilaments (6-7 nm) and short cytoplasmic processes. Spindle cells had long cytoplasmic processes and abundant intermediate- and microfilaments. These data provide further evidence for multiple bovine trabecular cell types. The smooth muscle-like spindle cell may represent the previously proposed contractile element of the angle and its action could conceivably alter ocular outflow resistance.
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PMID:Electrical and morphological evidence for heterogeneous populations of cultured bovine trabecular meshwork cells. 164 71

ATPase from isolated secretory granules was stimulated in a concentration-dependent manner by HCO3- above 0.9 mM. Maximal stimulation was found at about 16 mM HCO3- and was about half of that with sulphite (SO3(2-)). The activation site(s) appeared to be similar to at least one class of SO3(2-) sites, HCO3(-)-stimulate ATPase was inhibited by SITS. Furthermore, maximal stimulation with SO3(2-) was not enhanced with HCO3-. At low Mg2+ concentrations, Ca2+ stimulated granule ATPase. At higher concentrations of Mg2+ (0.5 mM and above), Ca2+ at 0.1 mM or less had little effect on HCO3(-)-ATPase, and Ca2+ at 4 mM inhibited HCO3(-)-ATPase. At concentrations of Ca2+ above 0.44 mM, the enzyme was partially stimulated in the absence of Mg2+ and presence of HCO3-. Mitochondrial contamination did not account for the presence of ATPase in the isolated granule fraction. The granule ATPase may be regulated by HCO3- and calcium and this could be related to changes in the granule environment during exocytosis.
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PMID:The effect of HCO3- on anion-stimulated ATPase from rat parotid granules. 165 95

The contractility of heart muscle is sensitive to the relative cytoplasmic concentrations of Na+, H+ and Ca++. The concentration of Na+ is mainly controlled by the Na+/K(+)-ATPase while the concentration of H+ is regulated by the Na+/H+ and Cl-/HCO3- exchanges. Cytoplasmic Ca++ concentration is mainly under the control of the sarcolemmal Na+/Ca++ exchange and Ca(++)-ATPase and sarcoplasmic reticular Ca(++)-ATPase. However, in heart muscle there is also a complex interaction between these ions such that altering the main regulation of one will affect the intracellular levels of the other two. Such interaction may thus enhance or attenuate the contractile response to the initial change. This review briefly describes the properties of the main regulatory mechanisms and focuses on their interactions and what consequences these have for contraction.
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PMID:Regulation and interaction of intracellular calcium, sodium and hydrogen ions in cardiac muscle. 165 99

The effect of isoproterenol on the electrophysiological properties of the S2 proximal segment of the rabbit was examined. Isoproterenol at 10(-8) to 10(-4) M depolarized the basolateral membrane voltage (Vb) in a dose-dependent manner. Propranolol attenuated the isoproterenol-induced depolarization. These possible mechanisms of cell depolarization were explored. The role of luminal Na(+)-organic solute cotransport was negligible, since the removal of organic solute did not change the depolarization. Basolateral Na(+)-(HCO3-) cotransport was supported by the finding that 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid inhibited isoproterenol-induced depolarization. Basolateral K+ conductance was suggested by the finding that the application of Ba2+ blocked the isoproterenol-induced depolarization. Na(+)-K(+)-adenosine-triphosphatase (ATPase) was questionable. Although ouabain blocked isoproterenol-induced depolarization, the removal of Na+ did not inhibit the depolarization. Further experiment revealed that dibutylyl-adenosine 3',5'-cyclic monophosphate (cAMP), 8-bromo cAMP, and forskolin did not mimic the response of isoproterenol. These results demonstrate: 1) there is a functional beta-adrenoceptor that depolarizes Vb; 2) isoproterenol-induced depolarization is due to an inhibition of basolateral K+ channel or the activation of basolateral Na(+)-(HCO3-)n cotransport; 3) isoproteronol-induced depolarization is independent of cAMP in the rabbit proximal tubule.
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PMID:Evidence for presence of functional beta-adrenoceptor in rabbit S2 proximal straight tubules. 165 31

The rat MTAL secretes protons into the tubular fluid and thus absorbs bicarbonate at substantial rates. Yet the cellular mechanisms of H+/HCO3- transport in the rat MTAL remain largely unsettled. We have performed intracellular pH recovery studies with use of the fluorescent probe BCECF in suspensions of rat MTAL fragments. Luminal H+ secretion occurs by two mechanisms (each responsible for 50% of the normal pHi recovery rate): (1) an electroneutral Na+/H+ antiporter that has an Na-Km of about 11 mM and is inhibited by amiloride (Ki = 2.8 x 10(-5) M); (2) a primary H+ pump that is inhibited by 10(-4) M NEM and 10(-4) M omeprazole, but not by 10(-4) M vanadate or removal of external K. These results suggest the presence of a vacuolar H(+)-ATPase rather than a H(+)-K(+)-ATPase. Basolateral HCO3 exit occurs predominantly by a Cl(-)- and Na(+)-independent electroneutral K+/HCO3- symporter, that has an HCO3-Km of about 17 mM, and is partially inhibited by 10(-4) M DIDS. Basolateral HCO3- efflux was not accompanied by variations of membrane potential monitored with the Em-sensitive fluorescent probe DIS-C3-5, and was not affected by maneuvers that depolarize the cells. It was strongly inhibited by cellular K depletion and dependent on transmembrane K gradient. We conclude that the rat MTAL should secrete protons through both Na+/H+ antiporter and H(+)-ATPase, and that basolateral HCO3- exit should occur through an electroneutral K+/HCO3- symporter.
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PMID:Mechanisms of H+/HCO3- transport in the medullary thick ascending limb of rat kidney. 165 72


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