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)

The direct effects of acute changes in K+ concentration on HCO-3 (JnettCO2) and volume reabsorption (Jv) were examined in isolated perfused rabbit proximal convoluted tubules (PCT). Increasing ambient K+ concentration from 5 to 8 mM did not change JnettCO2 (94.5 +/- 16.1 vs. 98.8 +/- 17.7 pmol X mm-1 X min-1) or Jv (1.27 +/- 0.15 vs. 1.24 +/- 0.16 nl X mm-1 X min-1). In contrast, reducing ambient K+ concentration from 5 to 2 mM inhibited JnettCO2 by 22% and Jv by 29%. Reducing luminal K+ concentration from 5 to 0 mM with constant bath K+ concentration at 5 mM did not affect JnettCO2 or Jv. Further reductions in bath K+ concentration to 0.5 and 0 mM showed a similar dependence of both fluxes on K+ concentration. Half-maximum inhibition of JnettCO2 was obtained at 1.1 mM ambient K+ concentration and of Jv at 0.85 mM. At zero bath K+ concentration JnettCO2 was 6.6 +/- 2.5 pmol X mm-1 X min-1 and Jv was 0.03 +/- 0.04 nl X mm-1 X min-1. To determine whether this rate of acidification was significantly different from zero, we examined the ability of the PCT to generate tCO2 concentration gradients with zero bath K+ concentration at slow perfusion rates. The tCO2 concentration gradient generated (0.94 mM) was not different from that found when the perfusate was inserted directly into the collection pipette in the absence of a tubule (0.71 mM). These data are consistent with the view that HCO-3 reabsorption is totally dependent on the Na+-K+-ATPase pump system.
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PMID:Effect of potassium concentration on bicarbonate reabsorption in the rabbit proximal convoluted tubule. 629 11

Studies on canalicular electrolyte transport are reviewed with reference to the concept that hepatocellular inorganic ion secretion may provide an osmotic drive for canalicular water flow. Cellular transport of electrolytes and of some nonelectrolytes appears directly or indirectly (cotransport or potential-sensitive transport) related to the activity of Na+-K+-ATPase of the sinusoidal cell membrane, but the role of the enzyme in regulating bile flow remains undetermined. Bile secretion of the isolated rat liver continues in the absence of either Na+, K+, Cl-, or HCO-3 when these ions are replaced in the perfusion medium by other permanent ions. Transepithelial salt concentration gradients, established experimentally, cause transient changes of bile flow and dissipate very quickly. Isotopic ion equilibration between sinusoids and bile proceeds faster than between sinusoids and liver cells. Both observations indicate extensive electrolyte diffusion through a paracellular shunt pathway. This pathway appears preferentially permeable to cations, and it restricts permeation of molecules of the size of sucrose (no apparent diffusion or effects of solvent drag) or bile acids (no backleak). In promoting canalicular osmotic water flow, transepithelial concentration gradients of NaCl are less effective than those of sucrose, revealing a reflection coefficient of NaCl of 0.3. By perfusion with hypertonic medium containing sucrose, bile flow is reduced. Bile production against this opposing osmotic gradient is accomplished by an increase in biliary organic anion concentration. Inorganic ion concentrations essentially conform to a Gibbs-Donnan distribution across the canalicular epithelium, established by the presence of impermeant anions in bile. Hence, the luminal electrical potential is expected to be negative with respect to the sinusoids. It is concluded that biliary secretion of endogenous organic anions is the major osmotic driving force for canalicular bile salt-independent bile flow and that transport of inorganic ions into bile results mainly from diffusion and solvent drag.
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PMID:Canalicular bile salt-independent bile formation: concepts and clues from electrolyte transport in rat liver. 629 15

The inhibitory effect of mercuric chloride on mouse kidney enzymes and the treatment of this inhibition with some thiol-containing compounds, e.g., dithiothreitol (DTT), dimercaptosuccinic acid (DMS) and D-penicillamine (Pen) was examined. To produce a significant inhibition of renal enzymes in vivo, it was necessary to administer 5 mg Hg/kg/day, s.c., once daily for 3 doses, and to sacrifice the animals 1 day after the last injection. With this Hg dose, microsomal Mg2+-Na+-K+-ATPase, mitochondrial Mg2+-HCO-3-ATPase and supernatant carbonic anhydrase activities decreased to about 30%, 70% and 60% of normal values, respectively. Combined administration of DTT (5-20 mg/kg, i.p.) and DMS (5-20 mg/kg, i.p.) with HgCl2 restored the enzyme activities to near normal or normal levels in parallel to the administered doses. The effect of Pen was slightly less than that of the above 2 compounds. This may be due to the number of thiol radicals, as Pen is a monothiol and the other 2 compounds are dithiol compounds. Since the toxicity of DMS is very low compared with DTT, DMS may be more suitable for the treatment of mercury poisoning.
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PMID:The protective effects of thiol-containing compounds on mercuric chloride-induced acute inhibition of enzymes from mouse kidney. 632 Apr 97

HCO-3 transport (JHCO-3) in early juxtamedullary proximal convoluted tubules isolated from infant rabbits during the 1st 3 wk of life is about one-third that in tubules obtained from adults. A rapid increase in transport ensues during wk 4 through 6, so that near-mature levels are attained by the end of this time. Because the pattern for development of glucose absorption was similar and because both HCO-3 and glucose absorption are driven by the lumen-to-cell Na+ flux, the activity of Na-K-ATPase (the Na+-extruding pump) was considered to be a critical mediator. A kinetic microassay (which couples ATP hydrolysis to NADH oxidation) allowed the measurement of Na-K-ATPase and ouabain-insensitive ATPase on the same tubular segment. Three to nine early juxtamedullary proximal convoluted tubules were obtained after collagenase treatment of the kidney and four to six rabbits were studied at each week of life. The mean activity of Na-K-ATPase during the 1st wk of life was 44.5 +/- 3.5 pmol X min-1 X mm-1, one-third of the adult level. During an interim period of development (2-6 wk), enzyme activity gradually reached 60% of adult levels (76.3 +/- 3.0 at 6 wk), while transport of HCO-3 and glucose, studied previously in other animals, attained mature rates. Only in the 7th wk did the enzyme activity reach that of the adult (106.8 +/- 6.8 in wk 7 vs. 128.4 +/- 14.0 in adult rabbits).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Development of solute transport in rabbit proximal tubule. III. Na-K-ATPase activity. 633 Nov 74

Sodium chloride transfer across isolated frog skin is described by the well-known Koefoed Johnsen-Ussing (KU) model, the central features of which are 1) a two-step, active, inward transport of Na+, and 2) passive cotransfer of Cl-, which is coupled electrically to Na+ movement under open-circuit conditions. However, NaCl absorption by the frog skin in vivo involves active inward transport of both ions by completely independent systems. Electrical neutrality is maintained by countertransfer of H+ (exchanged for Na+) and HCO-3 (exchanged for Cl-). This behavior is called the Krogh (KR) model. The KU and KR models share some features, notably amiloride sensitivity and participation of the Na+-K+-ATPase in Na+ transport, but the differences between them are fundamental. The latter appear to be due to the use of different experimental conditions. Intact frogs are usually studied in dilute (approximatley 1 mM) external solutions, while Ringer solution is used in most work on isolated skins. The skin is virtually impermeable to Cl- in dilute external media but permeable in Ringer solution. This concentration-dependent change in PCl can explain most of the differences between KU and KR models. Regulation of blood NaCl concentration in freshwater aquatic animals requires active uptake of both Na+ and Cl-. Data on representatives of four phyla show that the KR model describes the transport behavior in all of them. Such similarities in unrelated animals suggest that the transport mechanisms evolved very early in marine ancestors of modern freshwater forms. The implications of this suggestion are considered.
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PMID:Sodium chloride absorption across the body surface: frog skins and other epithelia. 634 May 29

The human large intestine absorbs Na+, Cl- and water from its lumen and secretes HCO-3 and some K+. The primary event in absorption is thought to be the active transport of Na+ ions out of the cell and across the baso-lateral cell membrane, by the energy requiring Na+-K+ ATPase. This leads in turn to Na+ entry into the cell via its luminal border and the creation of a potential across the mucosa which drives the transport of other ions. Cl- is coupled to HCO-3 secretion through a common carrier and K+ enters the intestinal lumen partly through an active secretory pathway. Most ions probably cross the epithelium by both transcellular and paracellular (shunt) pathways, water moving in response to solute transport. However the colon is not normally perfused by a saline-bicarbonate solution. It contains an active microflora which ferment 30 g or more of carbohydrate daily, derived from diet and intestinal secretions, with the production of at least 300 mmol of short chain fatty acids (acetic, propionic and butyric acids). About 6 g of urea is also degraded to NH3. These metabolic processes result in the generation of solutes which are then transported across the mucosa and which alter the pattern of water and electrolyte transport significantly. Short chain fatty acids are rapidly absorbed by passive diffusion as the undissociated acids, although anion transport, possibly through a paracellular route, is also feasible. Their absorption leads to the accumulation in the lumen of HCO3, a rise in pH, fall in pCO2 and stimulation of Na+ and water transport. The effect on Na+ transport is thought to indicate the presence of a Na+/H+ exchange in the cell membrane. The amounts of these organic solutes produced in the colon each day are probably greater than the total numbers of inorganic ions such as Na+, K+, Cl- and HCO-3 and as such must be taken into account in any understanding of overall transport processes in the large intestinal epithelium.
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PMID:Colonic absorption: the importance of short chain fatty acids in man. 637 78

An anion-stimulated, Mg2+-dependent, ouabain-insensitive ATPase is present in salt gland homogenates of domestic ducks (Anas platyrhynchos). The enzyme is unspecifically stimulated by various inorganic and organic anions including amino and sulfonic acids which are often used as buffer components (e. g. histidine, Bicin, PIPES, MES and HEPES). Therefore, the demonstration of ATPase stimulation by chloride strongly depends on the type and concentration of the buffer used and may also largely interfere with the stimulation caused by other anions present in the incubation medium. Of the inorganic anions tested chloride and bicarbonate appear to be the favorite physiological activators, but the possible role of carbonic acids in the stimulation of the anion-dependent ATPase should not be neglected. Km values are approximately 5.8 mM for Cl- and approximately 8.7 mM for HCO-3-activation. Maximal ATPase stimulation is obtained at 25 mM Cl- and approximately 30 mM HCO-3, respectively. The simultaneous presence of bicarbonate decreases chloride affinity and Vmax, and shifts the chloride optimum to lower concentrations. ATP is the most preferred substrate. Maximal activation by Cl- and HCO-3 occurs at ATP concentrations between 0.5 and 1 mM. ATP affinity increases in the presence of Cl- and HCO-3, respectively. Both chloride and bicarbonate require a Mg2+ to ATP ratio of approximately 0.5 and a pH value of 8.0 to 8.5 for optimal stimulation. Stimulation by Cl- and HCO-3 is inhibited by thiocyanate, cyanate and by the diuretic drugs furosemide, ethacrynic acid and mersalyl. Incubation media adapted for the simultaneous demonstration of both chloride and bicarbonate activation contained 10 to 20 mM histidine-Tris buffer at pH 8.0 to 8.5, 150 mM sucrose, 0.2 mM ouabain, 0.5 mM magnesium acetate, 1 mM ATP, (pH adjusted to 8.0-8.5 with Tris or NaOH), with and without 25 mM sodium chloride or 25 mM sodium bicarbonate.
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PMID:[Demonstration and properties of a Cl-/HCO3--ATPase in the avian salt gland (author's transl)]. 645 8

Proton transport across the plasma membrane of the gastrointestinal epithelium occurs by various pathways. There is the permeability of H+ across the lipid components of the membranes, probably of minor significance at physiological pH, but at the pH of the secretory surface of the parietal cell a factor that cannot be neglected. Transport of H+ dependent on the protein components of the plasma membrane involves various mechanisms. For example Na+ :H+ or Cl- :HCO-3 antiport (exchange) are generally electroneutral mechanisms (i.e., neither affected by potential gradients nor affecting membrane conductance) that are widely distributed throughout the body. Plasma membranes may contain proton or bicarbonate conductances (i.e., gradients of either ion may be determined by the potential across the membrane). This type of pathway is often of minor significance, hence the electrical component of hydrogen ion gradients across the plasma membrane can often be neglected. In the case of the gastric parietal cell, proton transport depends on the activity of a specific ATPase. This ATPase may be present elsewhere in the intestinal tract. This review will consider many of these proton pathways. In the case of brush border pathways, some of the data presented on Na+ :H+ antiport wil be derived from studies done on renal brush border rather than those of the small intestine, on the assumption that the properties of the antiporter are similar in the two tissues.
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PMID:Proton/hydroxyl transport in gastric and intestinal epithelia. 646 Jan 7

In order to increase our understanding of the mechanism of pancreatic fluid secretion we have studied the effects of various transport inhibitors on this process in the isolated rabbit pancreas. In this preparation, a high rate of unstimulated fluid secretion occurs, which probably originates from the ductular cells. Inhibitory are ouabain, furosemide, bumetanide, piretanide, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) and acetazolamide, with their half-inhibitory concentrations: 2 X 10(-6) M (ouabain), 1.3 X 10(-3) M (furosemide), 2.2 X 10(-3) M (bumetanide and piretanide) and 1.4 X 10(-4) M (SITS). With acetazolamide a maximal inhibition of only 20% is found at 10(-3) M. Amiloride (10(-3) M) has no effect on pancreatic fluid secretion. The inhibitory effects on HCO-3 output are always larger and those on Cl- output lower than those on fluid secretion. The results suggest that the ouabain-sensitive (Na+ + K+)-ATPase system provides the energy for a Na+-gradient-driven Cl--HCO-3-exchange transport system, sensitive to the loop diuretics furosemide, bumetanide and piretanide and to SITS. This system would drive the transcellular transport of HCO-3 and secondarily that of cations, Cl- and water.
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PMID:The mechanism of fluid secretion in the rabbit pancreas studied by means of various inhibitors. 649 95

The binding of N-acetyl-L-glutamate, the physiological allosteric activator, to rat liver carbamoyl-phosphate synthetase (ammonia) was studied by techniques of rate of dialysis and of ultracentrifugation in the Airfuge. There is one binding site for acetylglutamate per enzyme monomer (Mr 165 000). K+, Mg2+ (free) and ATP were required to demonstrate binding. The concentrations of ATP required indicate that binding of ATPA (the ATP molecule that yields Pi) is needed. HCO-3 was not essential, but it enhanced binding of acetylglutamate. Glycerol also favored binding. Plots of Kd values versus the reciprocal of free Mg2+ and ATP concentrations are linear and indicate that ATPA, K+ and Mg2+ bind before acetylglutamate. In the presence of these ligands and HCO-3, ammonia increased drastically the Kd value for acetylglutamate, whereas in absence of HCO-3 ammonia had little effect. This suggests that acetylglutamate dissociates with the products and explains the higher Km for acetylglutamate in the synthetase (overall) reaction than in the ATPase (partial) reaction. In the absence of ATP acetylglutamate was bound with high affinity if ADP and carbamoyl phosphate were present. ADP or carbamoyl phosphate alone did not promote substantial binding. Binding of acetylglutamate at low concentration was slow; it was accelerated at higher concentrations of the activator. Exchange of bound acetylglutamate with acetylglutamate in solution was fast. A scheme proposed earlier for allosteric activation of the enzyme [Rubio, V., Britton, H. G. and Grisolia, S. (1983) Eur. J. Biochem. (in preparation)] is refined to incorporate the new information. Binding of ATPA, K+ and Mg2+ and formation of 'active CO2' (the central complex) are greatly favored by acetylglutamate.
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PMID:Binding of N-acetyl-L-glutamate to rat liver carbamoyl phosphate synthetase (ammonia). 688 68


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