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PubMedDate not supplied

Effects of L-phenylalanine on acetylcholinesterase, (Na+,K+)-ATPase and Mg2+-ATPase activities in adult rat whole brain and frontal cortex.

The effect of different L-phenylalanine (Phe) concentrations (0.12-12.1 mM) on acetylcholinesterase (AChE), (Na+,K+)-ATPase and Mg2+-ATPase activities was investigated in homogenates of adult rat whole brain and frontal cortex at 37 degrees C. AChE, (Na+,K+)-ATPase and Mg2+-ATPase activities were determined after preincubation with Phe. AChE activity in both tissues showed a decrease up to 18% (p<0.01) with Phe. Whole brain Na+,K+-ATPase was stimulated by 30-35% (p<0.01) with high Phe concentrations, while frontal cortex Na+,K+-ATPase was stimulated by 50-55% (p<0.001). Mg2+-ATPase activity was increased only in frontal cortex with high Phe concentrations. It is suggested that: a) The inhibitory effect of Phe on brain AChE is not influenced by developmental factors, while the stimulation of Phe on brain Na+,K+-ATPase is indeed affected; b) The stimulatory effect of Phe on rat whole brain Na+,K+-ATPase is decreased with age; c) Na+,K+-ATPase is selectively more stimulated by high Phe concentrations in frontal cortex than in whole brain homogenate; d) High (toxic) Phe concentrations can affect Mg2+-ATPase activity in frontal cortex, but not in whole brain, thus modulating the amount of intracellular Mg2+.

Acetylcholinesterase↗

PubMed1995

Colocalization of H-ATPase and H,K-ATPase immunoreactivity in the rat kidney.

Urinary acidification in the collecting duct (CD) is via V-type H-ATPase and P-type H,K-ATPase. The localization and polar distribution of H-ATPase in intercalated cells (IC) have been well studied. The localization of H,K-ATPase to IC has been reported, but its intracellular distribution has not been defined. To colocalize these pumps, a murine monoclonal antibody (E11) to the 31-kd subunit of the H-ATPase and a rabbit antiserum (HK alpha N2) to a synthetic peptide based on the N terminus of the hog gastric H,K-ATPase alpha-subunit were used. In immunocytochemical staining of rat kidney, H,K-ATPase was present only in the IC of the CD with the same polar distribution as H-ATPase. The preabsorption of HK alpha N2 with affinity-purified bovine H-ATPase did not affect the H,K-ATPase staining, whereas preabsorption with the immunizing synthetic peptide eliminated immunoreactivity. HK alpha N2 stained only parietal cells in the rat gastric mucosa, whereas preimmune serum and E11 showed no immunoreactivity. On immunoblots of rat gastric mucosal microsomes, HK alpha N2 labeled a single 94-kd band, and this staining disappeared after preabsorption with the immunizing synthetic peptide. HK alpha N2 labeled no bands on immunoblots of affinity-purified bovine H-ATPase. All immunochemistry was negative with preimmune serum.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1998

[Simultaneous assay of Ca(2+)-ATPase and Na+, K(+)-ATPase activities of osteoblast rat by malachite green colorimetic method].

The aim of this study was to find a method to measure simultaneously the activities of Ca(2+)-ATPase and Na+, K(+)-ATPase of rat osteoblast membrane. In this test, Ca(2+)-ATPase and Na+, K(+)-ATPase released inorganic phosphate (Pi) from ATP, and Pi was determined by colorimetric method using malachite green dye to show ATPase activities. Ca2+ concentration and osteoblast culture generation were important factors affecting ATPase activities. Ca2+ could elevate membrane ATPase activity. When Ca2+ concentration reached 40 mumol/L, ATPase activities were improved. Ca(2+)-ATPase activity decreased with the increase of osteoblast culture generation. Ca(2+)-ATPase activity was lower than Na+, K(+)-ATPase activity in osteoblast membrane. This method is simple, sensitive and reliable.

Animals↗

PubMed1993

Ca(2+)-dependent and thapsigargin-inhibited phosphorylation of Na+,K(+)-ATPase catalytic domain following chimeric recombination with Ca(2+)-ATPase.

Two chimeric proteins comprising the Na,K-ATPase catalytic domain (large cytosolic loop) and the two flanking regions of the Ca-ATPase were obtained by transient or stable expression in mammalian cells transfected with recombinant DNA. In the first chimera (CpNC), a large portion (containing the nucleotide-binding site) of the cytosolic loop between putative membrane spans M4 and M5 of the sarcoendoplasmic reticulum Ca2+ (SERCA) 1 (fast muscle) ATPase was replaced by the corresponding portion of the Na,K-ATPase alpha 1 subunit. In the second chimera (CNpC), an even larger portion (containing the nucleotide-binding site and the phosphorylation site) of the analogous cytosolic loop of the SERCA2 (cardiac muscle) ATPase was replaced by the corresponding portion of the Na,K-ATPase alpha 1 subunit. Steady state Ca2+ transport and coupled ATP hydrolysis by the chimeric proteins were negligible as compared to those obtained with SERCA enzymes. Nevertheless, the chimeric proteins were able to utilize ATP to form phosphoenzyme levels equal to those formed by SERCA ATPases. Chimeric and SERCA enzymes exhibited an identical Ca2+ requirement for ATP utilization and sensitivity to thapsigargin (TG) which is a specific inhibitor of SERCA ATPase and not of Na,K-ATPase. Furthermore, both SERCA and chimeric enzymes could be phosphorylated with P(i), and this reaction required removal of Ca2+. In comparative experiments, the functional pattern of seemingly unaffected phosphoenzyme formation and inhibited Ca2+ transport was produced in the SERCA ATPase even by single mutation of Pro337 to Ala, evidently due to defective protein conformation. Retention of Ca2+ and TG sensitivity by the chimeric proteins demonstrates that the Ca(2+)- and TG-binding domains do not reside within the cytosolic loop replaced by chimeric substitution and strongly support previous studies suggesting that binding of calcium required for enzyme activation occurs within the membrane-bound region of the SERCA ATPases (Clarke et al., 1989a; Sumbilla et al., 1991).

Amino Acid Sequence↗

PubMed2005

Inhibition of Na+/K(+)-ATPase and Mg(2+)-ATPase by metal ions and prevention and recovery of inhibited activities by chelators.

Kinetics and inhibition of Na(+)/K(+)-ATPase and Mg(2+)-ATPase activity from rat synaptic plasma membrane (SPM), by separate and simultaneous exposure to transition (Cu(2+), Zn(2+), Fe(2+) and Co(2+)) and heavy metals (Hg(2+) and Pb(2+)) ions were studied. All investigated metals produced a larger maximum inhibition of Na(+)/K(+)-ATPase than Mg(2+)-ATPase activity. The free concentrations of the key species (inhibitor, MgATP(2-), MeATP(2-)) in the medium assay were calculated and discussed. Simultaneous exposure to the combinations Cu(2+)/Fe(2+) or Hg(2+)/Pb(2+) caused additive inhibition, while Cu(2+)/Zn(2+) or Fe(2+)/Zn(2+) inhibited Na(+)/K(+)-ATPase activity synergistically (i.e., greater than the sum metal-induced inhibition assayed separately). Simultaneous exposure to Cu(2+)/Fe(2+) or Cu(2+)/Zn(2+) inhibited Mg(2+)-ATPase activity synergistically, while Hg(2+)/Pb(2+) or Fe(2+)/Zn(2+) induced antagonistic inhibition of this enzyme. Kinetic analysis showed that all investigated metals inhibited Na(+)/K(+)-ATPase activity by reducing the maximum velocities (V(max)) rather than the apparent affinity (Km) for substrate MgATP(2-), implying the noncompetitive nature of the inhibition. The incomplete inhibition of Mg(2+)-ATPase activity by Zn(2+), Fe(2+) and Co(2+) as well as kinetic analysis indicated two distinct Mg(2+)-ATPase subtypes activated in the presence of low and high MgATP(2-) concentration. EDTA, L-cysteine and gluthathione (GSH) prevented metal ion-induced inhibition of Na(+)/K(+)-ATPase with various potencies. Furthermore, these ligands also reversed Na(+)/K(+)-ATPase activity inhibited by transition metals in a concentration-dependent manner, but a recovery effect by any ligand on Hg(2+)-induced inhibition was not obtained.

Animals↗

PubMed2000

Colonic H-K-ATPase alpha- and beta-subunits express ouabain-insensitive H-K-ATPase.

Active K absorption in the rat distal colon is energized by an apical H-K-ATPase, a member of the gene family of P-type ATPases. The H-K-ATPase alpha-subunit (HKcalpha) has been cloned and characterized (together with the beta-subunit of either Na-K-ATPase or gastric H-K-ATPase) in Xenopus oocytes as ouabain-sensitive (86)Rb uptake. In contrast, HKcalpha, when expressed in Sf9 cells without a beta-subunit, yielded evidence of ouabain-insensitive H-K-ATPase. Because a beta-subunit (HKcbeta) has recently been cloned from rat colon, this present study was initiated to determine whether H-K-ATPase and its sensitivity to ouabain are expressed when these two subunits (HKcalpha and HKcbeta) are transfected into a mammalian cell expression system. Transfection of HEK-293 cells with HKcalpha and HKcbeta cDNAs resulted in the expression of HKcalpha and HKcbeta proteins and their delivery to plasma membranes. H-K-ATPase activity was identified in crude plasma membranes prepared from transfected cells and was 1) saturable as a function of increasing K concentration with a K(m) for K of 0.63 mM; 2) inhibited by orthovanadate; and 3) insensitive to both ouabain and Sch-28080. In parallel transfection studies with HKcalpha and Na-K-ATPase beta1 cDNAs and with HKcalpha cDNA alone, there was expression of ouabain-insensitive H-K-ATPase activity that was 60% and 21% of that in HKcalpha/HKcbeta cDNA transfected cells, respectively. Ouabain-insensitive (86)Rb uptake was also identified in cells transfected with HKcalpha and HKcbeta cDNAs. These studies establish that HKcalpha cDNA with HKcbeta cDNA express ouabain-insensitive H-K-ATPase similar to that identified in rat distal colon.

Animals↗

PubMed1996

A comparative study of (Ca(2+)-Mg2+)-ATPase on the lysosomal membrane and ecto-ATPase on the plasma membrane from rat liver.

We showed that rat liver lysosomes possess at least two types of ATPase besides H(+)-translocating ATPase (H(+)-ATPase); namely, N-ethylmaleimide (NEM)-sensitive and bafilomycin A1-insensitive Mg(2+)-ATPase [ATPase I] and NEM- and bafilomycin A1-insensitive (Ca(2+)-Mg2+)-ATPase [ATPase II] [Hayashi H., et al. Chem. Pharm. Bull., 37, 2783-2786 (1992)]. Subcellular fractionation showed the presence of similar activity of (Ca(2+)-Mg2+)-ATPase not only in the Golgi but also in the plasma membrane fractions, of which plasma membrane had the highest activity, most probably due to the ecto-ATPase. In this study, we partially purified the (Ca(2+)-Mg2+)-ATPases from both lysosomal and plasma membranes and compared their properties. Both enzymes had quite similar characteristics including: (1) broad pH-activity profiles with two pH optima at 4.5 and 7.0, (2) K(m) values for ATP being 21-27 microM (at pH 4.5) and 18-14 microM (at pH 7.0) (in the presence of CaCl2), (3) hydrolysis of both nucleoside triphosphates and diphosphate (ADP), (4) inhibition only by vanadate and 4,4'-diisothiocyanatostilbene 2,2'-disulfonic acid (DIDS) at pH 4.0 (but not at pH 7.0), (5) acidic pI values that were shifted by neuraminidase digestion, and (6) a positive reaction against an antibody to the N-terminal peptide of ecto-ATPase.

Adenosine Triphosphatases↗

PubMed1991

Respective roles of H-ATPase and H-K-ATPase in ion transport in the kidney.

Two types of proton-translocating ATPases, H-ATPase and H-K-ATPase, are found in the renal tubular cells. H-ATPase is present in both endocytic vesicles and apical membranes in almost all nephron segments. On the other hand, H-K-ATPase is present only in the connecting tubule and collecting duct. There is evidence to suggest that H-ATPase may be involved in H secretion in almost all nephron segments. H-K-ATPase is involved not only in H secretion but also in K absorption in the collecting duct segments. Aldosterone administration and metabolic acidosis stimulate the activity of H-ATPase in all collecting duct segments, whereas hypokalemia has only a limited effect on H-ATPase activity. On the other hand, hypokalemia, as well as metabolic acidosis, stimulates H-K-ATPase activity in the collecting duct segments, whereas aldosterone administration alone plays a minor role in the regulation of this enzyme. The physiological role and regulation of H-ATPase in the proximal tubule has not been established.

Biological Transport, Active↗

PubMed1990

Thermus thermophilus membrane-associated ATPase. Indication of a eubacterial V-type ATPase.

An ATPase with Mr of 360,000 was purified from plasma membranes of a thermophilic eubacterium Thermus thermophilus, and was characterized. ATP hydrolytic activity of the purified enzyme was extremely low, 0.07 mumol of Pi released mg-1 min-1, and it was stimulated up to 30-fold by bisulfite. The following properties of the enzyme indicate that it is not a usual F1-ATPase but that it belongs to the V-type ATPase family, another class of ATPases found in membranes of archaebacteria and eukaryotic endomembranes. Among its four kinds of subunits with approximate Mr values of 66,000 (alpha), 55,000 (beta), 30,000 (gamma), and 12,000 (delta), the alpha subunit had a similar molecular size to the catalytic subunits of the V-type ATPases but was significantly larger than the alpha subunit of F1-ATPases. ATP hydrolytic activity was not affected by azide, an inhibitor of F1-ATPases, but was inhibited by nitrate, an inhibitor of the V-type ATPase. N-terminal amino acid sequences determined for the purified alpha and beta subunits showed much higher similarity to those of the V-type ATPases than those of F1-ATPases. Thus the distribution of the V-type ATPase in the prokaryotic kingdom may not be restricted to archaebacteria.

Amino Acid Sequence↗

PubMed1982

Trifluoperazine inhibition of calmodulin-sensitive Ca2+ -ATPase and calmodulin insensitive (Na+ +K+)- and Mg2+ -ATPase activities of human and rat red blood cells.

Trifluoperazine dihydrochloride-induced inhibition of calmodulin-activated Ca2+ -ATPase and calmodulin-insensitive (Na+ +K+)- and Mg2+ -ATPase activities of rat and human red cell lysates and their isolated membranes was studied. Trifluoperazine inhibited both calmodulin-sensitive and calmodulin-insensitive ATPase activities in these systems. The concentration of trifluoperazine required to produce 50% inhibition of calmodulin-sensitive Ca2+ -ATPase was found to be slightly lower than that required to produce the same level of inhibition of other ATPase activities. Drug concentrations which inhibited calmodulin-sensitive ATPase completely, produced significant reduction in calmodulin-insensitive ATPases as well. The data presented in this report suggest that trifluoperazine is slightly selective towards calmodulin-sensitive Ca2+ -ATPase but that it is also capable of inhibiting calmodulin-insensitive (Na+ +K+)-ATPase and Mg2+ -ATPase activities of red cells at relatively low concentrations. Thus the action of the drug is not due entirely to its interaction with calmodulin-mediated processes, and trifluoperazine cannot be assumed to be a selective inhibitor of calmodulin interactions under all circumstances.

Adenosine Triphosphatases↗

PubMed1984

Erythrocyte membrane ATPase activity of G6PD-deficient individuals and the effect of primaquine metabolite(s) on membrane ATPase enzymes.

Erythrocyte membrane Na+/K+, Ca2+/Mg2+ and Mg2+ ATPase activities in addition to the calmodulin-activated Ca2+/Mg2+ ATPase enzyme were measured in both G6PD-deficient and normal individuals. Although all three membrane ATPase activities were somewhat higher in the G6PD-deficient erythrocytes, only activated Ca2+/Mg2+ ATPase activity was significantly increased. The effect of primaquine on the membrane ATPases was also compared with other ATPase inhibitors. Primaquine was ineffective on erythrocyte membrane ATPase in-vitro. However, sera containing primaquine metabolite(s) were inhibitory to Ca2+/Mg2+ and Mg2+ ATPase systems of only G6PD-deficient erythrocytes. Other ATPase inhibitors showed a similar inhibitory effect in G6PD-deficient and normal erythrocytes, indicating a specific influence of primaquine on ATPase system in G6PD deficiency. It is suggested that this effect of primaquine may be an additional factor for haemolysis observed in the people with GdB- type of G6PD deficiency among the Mediterranean populations.

Adenosine Triphosphatases↗

PubMed1976

Characterization of Mg-ATPase and (Na+ + K+)-stimulated Mg-ATPase in smooth muscular cells of the sheep's common carotid artery.

The Mg-ATPase and (Na+ + K+)-stimulated Mg-ATPase in the mitochondrial and microsomal fraction of smooth muscular cells of the sheep's common carotid artery have been characterized in more detail. Optimal enzyme activities were found for all ATPases to be at pH 7.5-8.0 and 45 degrees C-50 degrees C. The energies of activation were found to be at 5-9 kcal/mole for both ATPases. Two-thirds of the (Na+ + K+)-stimulated Mg-ATPase were found to be ouabain-sensitive and thus attributed to the coupled (Na, K)-transport system. The pI 50 values of ouabain for microsomal and mitochondrial fractions are 6.3 and 6.0, respectively. The highest activity of (Na+ + K+)-stimulated Mg-ATPase is at 5-10 mM K+ and more than 50 mM Na+. One-third of the (Na+ + K+)-stimulated Mg-ATPase activity was found to be due to a stimulation of Mg-ATPase by Na+ alone, which is not inhibited by ouabain. The relationship of this activity to the ouabain-sensitive part of the (Na+ + K+)-stimulated Mg-ATPase and to Na+-transport is discussed. For the Mg-ATPases apparent KM(ATP) values were determined to be 1.4 and 1.0 mM, resp., and for the (Na+ + K+)-stimulated Mg-ATPases 0.15 and 0.14 mM, resp.

Adenosine Triphosphatases↗

PubMed1995

The C-terminal 165 amino acids of the plasma membrane Ca(2+)-ATPase confer Ca2+/calmodulin sensitivity on the Na+,K(+)-ATPase alpha-subunit.

The C-terminal 165 amino acids of the rat brain plasma membrane (PM) Ca(2+)-ATPase II containing the calmodulin binding auto-inhibitory domain was connected to the C-terminus of the ouabain sensitive chicken Na+,K(+)-ATPase alpha 1 subunit. Expression of this chimeric molecule in ouabain resistant mouse L cells was assured by the high-affinity binding of [3H]ouabain. In the presence of Ca2+/calmodulin, this chimeric molecule exhibited ouabain inhibitable Na+,K(+)-ATPase activity; the putative chimeric ATPase activity was absent in the absence of Ca2+/calmodulin and activated by Ca2+/calmodulin in a dose-dependent manner. Furthermore, this chimeric molecule could bind monoclonal IgG 5 specific to the chicken Na+,K(+)-ATPase alpha 1 subunit only in the presence of Ca2+/calmodulin, suggesting that the epitope for IgG 5 in this chimera is masked in the absence of Ca2+/calmodulin and uncovered in their presence. These results propose a direct interaction between the calmodulin binding auto-inhibitory domain of the PM Ca(2+)-ATPase and the specific regions of the Na+,K(+)-ATPase alpha 1 subunit that are structurally homologous to the PM Ca(2+)-ATPase. A comparison of the deduced amino acid sequences revealed several possible regions within the Na+,K(+)-ATPase that might interact with the auto-inhibitory domain of the PM Ca(2+)-ATPase.

Adenosine Triphosphatases↗

PubMed2005

The protective effect of L-cysteine and glutathione on the adult and aged rat brain (Na+,K+)-ATPase and Mg2+-ATPase activities in galactosemia in vitro.

The aim of this study was to evaluate whether the addition of the antioxidants L-cysteine (Cys) or the reduced glutathione (GSH) could reverse the alterations of brain total antioxidant status (TAS) and the modulated activities of the enzymes (Na+,K+)-ATPase, and Mg2+-ATPase in adult or aged rat brain homogenates induced by galactosemia in vitro. Mixture A [mix. A: galactose-1-phosphate (Gal-1-P, 2 mM) plus galactitol (Galtol, 2 mM) plus galactose (Gal, 4 mM) = classical galactosemia] or mixture B [mix. B: Galtol (2 mM) plus Gal (1 mM) = galactokinase deficiency galactosemia] were preincubated in the presence or absence of Cys (0.83 mM) or GSH (0.83 mM) with adult or aged brain homogenates at 37 degrees C for 1 h. TAS and the enzyme activities were determined spectrophotometrically. Mix. A or mix. B preincubation with the adult brain resulted in a significant (Na+,K+)-ATPase inhibition (-30%) and a Mg2+-ATPase stimulation (+300% and +33%, respectively), whereas lower modifications of the enzyme activities (p < 0.001) were found in the aged brain. Gal mixtures decreased TAS by 40% (p < 0.001) and by 20% (p < 0.01) in adult and aged samples, respectively. The antioxidants significantly increased TAS resulting in the reversion of (Na+,K+)-ATPase inhibition and Mg2+-ATPase stimulation by mix. B only. The inhibitory effect of Gal and its derivatives on brain (Na+,K+)-ATPase and their stimulatory effect on Mg2+-ATPase are being decreased with age, probably due to the producion of free radicals. Cys and GSH increased TAS resulting in a reversion of the inhibited (Na+,K+)-ATPase in both models of the in vitro galactosemia and the stimulated Mg2+-ATPase in galactokinase deficiency galactosemia only.

Age Factors↗

PubMed1992

Immunological relatedness of the sarcoplasmic reticulum Ca(2+)-ATPase and the Na+,K(+)-ATPase.

The effect of anti-ATPase antibodies with epitopes near Asp-351 (PR-8), Lys-515 (PR-11) and the ATP binding domain (D12) of the Ca(2+)-ATPase of sarcoplasmic reticulum (EC 3.6.1.38) was analyzed. The PR-8 and D12 antibodies reacted freely with the Ca(2+)-ATPase in the native membrane, indicating that their epitopes are exposed on the cytoplasmic surface. Both PR-8 and D12 interfered with the crystallization of the Ca(2+)-ATPase, suggesting that their binding sites are at interfaces between ATPase molecules. PR-11 had no effect on ATPase-ATPase interactions or on the ATPase activity of sarcoplasmic reticulum. The epitope of PR-11 is suggested to be the VIDRC sequence at residues 520-525, while that of D12 at residues 670-720 of the Ca(2+)-ATPase. The use of predictive algorithms of antigenicity for identification of potential antigenic determinants in the Ca(2+)-ATPase is analyzed.

Amino Acid Sequence↗

PubMed1998

CI-ATPase and Na+/K(+)-ATPase activities in Alzheimer's disease brains.

The enzyme activities and the protein levels of Cl(-)-ATPase and Na+/K(+)-ATPase were examined in Alzheimer's disease (AD) brains. Cl(-)-ATPase and Na+/K(+)-ATPase activities in AD brains (n = 13) were significantly lower than those in age-matched control brains (n = 12). In contrast, there was no significant difference in anion-insensitive Mg2(+)-ATPase activity between the two groups. Western blot analysis revealed that the protein levels of Cl(-)-ATPase, Na+/K(+)-ATPase and neuron specific Na+/K(+)-ATPase alpha3 isoform were also significantly reduced in AD brains, while the amount of protein disulfide isomerase, one of the house keeping membrane proteins, was not different between the two groups. The data first demonstrated that Cl(-)-ATPase and Na+/K(+)-ATPase are selectively impaired in AD brains, which may reduce the gradients of Na(+), K(+) and Cl(-) across the cell membranes to cause excitotoxic cellular response and the resulting neuronal death.

Adenosine Triphosphatases↗

PubMed1997

Adaptation to low-K+ media increases H(+)-K(+)-ATPase but not H(+)-ATPase-mediated pHi recovery in OMCD1 cells.

Studies in rat and rabbit outer medullary collecting duct of inner stripe origin (OMCDis) suggest that both H(+)-ATPase and H(+)-K(+)-ATPase participate in H+ secretion. However, the relative contributions of these transporters, and, in particular, that of H(+)-K(+)-ATPase to K+ absorption have not been defined precisely. The present study was designed to delineate more clearly the response of these two transporters to hypokalemia and acidosis in a newly developed mouse OMCD1 cell line. In cells grown in normal K+ (5 mM) media, intracellular pH (pHi) recovery was similar either in the presence or absence of K+ in the perfusate (delta pHi/min = 0.014 +/- 0.001 vs. 0.017 +/- 0.003, not significant). The inhibitory effects of Sch-28080 (10 microM) and bafilomycin A1 (10 nM) on pHi recovery were evident only in the presence and absence of K+ in the perfusate, respectively. In cells grown in low-K+ (2.5 mM) media to simulate chronic hypokalemia, pHi recovery was significantly faster than in cells grown in normal K+ media (delta pHi/min = 0.045 +/- 0.01 vs. 0.014 +/- 0.001, P < 0.01) and was inhibited specifically by Sch-28080, not by bafilomycin A1. In contrast, in cells preconditioned to low pH (7.0) to simulate chronic acidosis, the enhanced pHi recovery was abolished by bafilomycin A1 but not by Sch-28080. 86Rb+ uptake, when used as a K+ congener, was inhibited by Sch-28080. The K(m) for 86Rb+ uptake (H(+)-K(+)-ATPase activity) and the 50% inhibitory concentration for Sch-28080 were 270 and 5.0 microM, respectively. These studies provide evidence that, in morphologically homogeneous OMCD1 cells, 1) both H(+)-K(+)-ATPase and H(+)-ATPase participate in pHi regulation, 2) the H(+)-K(+)-ATPase is selectively upregulated by preconditioning in low-K+ media, and 3) conversely, preconditioning in low-pH media stimulates only the H(+)-ATPase. Thus, in OMCDis, the H(+)-K(+)-ATPase and H(+)-ATPase respond selectively and independently to chronic hypokalemia and acidosis, respectively.

Adaptation, Physiological↗

PubMed1995

Lithium-induced inhibition of Na-K ATPase and Ca ATPase activities in rat brain synaptosome.

To explore the action mechanism of lithium in the brain, the author investigated the effects of lithium on Na-K ATPase and Ca ATPase in rat brain synaptosomes prepared from forebrains by the method of Booth and Clark. The activities of Na-K ATPase and Ca ATPase were assayed by the level of inorganic phosphate liberated from the hydrolysis of ATP. Lithium at the optimum therapeutic concentration of 1 mM decreased the activity of Na-K ATPase from the control value of 19.08 +/- 0.29 to 18.27 +/- 0.10 micromoles Pi/mg protein/h and also reduced the activity of Ca ATPase from 6.38 +/- 0.12 to 5.64 +/- 0.12 micromoles Pi/mg protein/h. The decreased activity of Na-K ATPase will decrease the rate of Ca2+ efflux, probably via an Na-Ca exchange mechanism and will increase the rate of Ca2+ entry by the depolarization of nerve terminals. The reduced activity of Ca ATPase will result in the decreased efflux of Ca2+. As a Conclusion, it can be speculated that lithium elevates the intrasynaptosomal Ca2+ concentration via inhibition of the activities of Na-K ATPase and Ca ATPase, and this increased [Ca2+]i will cause the release of neurotransmitters and neurological effects of lithium.

Animals↗