V-H(+)-ATPase, Na(+)/K(+)-ATPase and NHE2 immunoreactivity in the gill epithelium of the Pacific hagfish (Epatretus stoutii)

We report the presence of the ion transporting proteins V-H(+)-ATPase, Na(+)/K(+)-ATPase and NHE2 in the gill epithelium of the Pacific hagfish Epatretus stoutii. Heterologous antibodies recognized single bands of the appropriate sizes for the three transporters in western blots. Immunohistochemical staining revealed that the distribution of labeled cells in the gill epithelium was identical for the three proteins. Immunopositive cells were most abundant in the primary filament from the afferent side of the gill pouch, and their number diminished towards the lamella. Na(+)/K(+)-ATPase-like immunoreactivity (L-IR) occurred throughout the cell cytoplasm, probably associated to the basolateral tubular system. V-H(+)-ATPase L-IR was similar to Na(+)/K(+)-ATPase, although some cells had slightly heavier staining in either the supra- or infra-nuclear region. NHE2 L-IR was also generally cytoplasmic, but a minority of the cells had stronger immunoreactivity in the apical region. In general, all three ion transporting proteins were localized in the same cells, as estimated from 4-microm immunostained consecutive sections. We hypothesize that these putative ion-transporting cells are involved in systemic acid/base regulation and discuss other possible roles. This is the first report of V-H(+)-ATPase in myxinoids, and the first NHE2 report in the Pacific hagfish.     

Immunocytochemical localization of Na+,K(+)-ATPase in rat retinal pigment epithelial cells

We investigated quantitatively the ultrastructural localization of the alpha-subunit of Na+,K(+)-ATPase in rat retinal pigment epithelial cells by the protein A-gold technique, using an affinity-purified antibody against the alpha-subunit of rat kidney Na+,K(+)-ATPase. Immunoblot analysis showed that the antibody bound specifically to the alpha- and alpha(+)-subunits of Na+,K(+)-ATPase in the whole retina [the sensory retina plus retinal pigment epithelium (RPE)]. Rat eyes were fixed by perfusion with 4% paraformaldehyde containing 1% glutaraldehyde and embedded in Lowicryl K4M. Ultra-thin sections were incubated with affinity-purified antibody against the alpha-subunit of rat kidney Na+,K(+)-ATPase and subsequently with protein A-gold complex. Light microscopy with a silver enhancement procedure revealed Na+,K(+)-ATPase localized to both the apical and the basal plasma membrane domains of the RPE. Quantitative immunocytochemical analysis by electron microscopy showed a higher density of gold particles on the apical surface than on the basolateral one. Microvilli are so well developed on the apical surface of the RPE that the apical surface profile is much longer than the basolateral one. This means that Na+,K(+)-ATPase is mainly located on the apical surface of the RPE cells.     

A monoclonal antibody against a native conformation of the porcine renal Na+/K(+)-ATPase alpha-subunit protein

A monoclonal antibody (mAb50c) against the native porcine renal Na+/K(+)-transporting adenosinetriphosphatase (EC 3.6.1.37, ATP phosphohydrolase) (Na+/K(+)-ATPase) was characterized. The antibody could be classified as a conformation-dependent antibody, since it did not bind to Na+/K(+)-ATPase denatured by detergent and its binding was affected by the normal conformational changes of the enzyme induced by ligands. The binding was the greatest in the presence of Na+, ATP or Mg2+ (E1 form), slightly less in the presence of K+ (E2K form) and the least when the enzyme was phosphorylated, especially in the actively hydrolyzing form in the presence of Na+, Mg2+ and ATP. The antibody inhibited both the Na+,K(+)-ATPase activity and the K(+)-dependent p-nitrophenylphosphatase activity by 25%, but it had no effect on Na(+)-dependent ATPase activity. The antibody partially inhibited the fluorescence changes of the enzyme labeled with 5'-isothiocyanatofluorescein after the addition of orthophosphate and Mg2+, and after the addition of ouabain. Proteolytic studies suggest that a part of the epitope is located on the cytoplasmic surface of the N-terminal half of the alpha-subunit.     

Immunolocalization of Na+,K+-ATPase in the organs of the branchial cavity of the European lobster Homarus gammarus (Crustacea, Decapoda)

The localization of Na+,K(+)-ATPase in epithelia of the organs of the branchial cavity of Homarus gammarus exposed to seawater and dilute seawater was examined by immunofluorescence microscopy and immunogold electron microscopy with a monoclonal antibody IgG alpha 5 raised against the avian alpha-subunit of the Na-,K(+)-ATPase. In juveniles held in seawater, fluorescent staining was observed only in the epithelial cells of epipodites. In juveniles held in dilute seawater, heavier immunoreactivity was observed in the epithelial cells of epipodites, and positive immunostaining was also observed along the inner-side epithelial layer of the branchiostegites. No fluorescent staining was observed in the gill epithelia. At the ultrastructural level, the Na+,K(+)-ATPase was localized in the basolateral infolding systems of the epipodite and inner-side branchiostegite epithelia of juveniles held in dilute seawater, mostly along the basal lamina. The expression of Na+,K(+)-ATPase therefore differs within tissues of the branchial cavity and according to the external salinity. These and previous ultrastructural observations suggest that the epipodites, and to a lesser extent the inner-side epithelium of the branchiostegites, are involved in the slight hyper-regulation displayed by lobsters at low salinity. Enhanced Na+,K(+)-ATPase activity and de novo synthesis of Na+,K(+)-ATPase within the epipodite and branchiostegite epithelia may be key points enabling lobsters to adapt to low salinity environments.     

Recovery from blood alkalosis in the Pacific hagfish (Eptatretus stoutii): involvement of gill V-H+-ATPase and Na+/K+-ATPase

To investigate the base secretory mechanisms in the Pacific hagfish (Eptatretus stoutii), we injected animals with NaHCO3 into the subcutaneous sinus. In the first series of experiments, hagfish were injected with 6000 micromol kg(-1) NaHCO3 (base-infused hagfish, BIH) or NaCl (controls). Blood pH increased significantly 1 h after injection in BIH (8.05+/-0.05 vs. 7.82+/-0.03 pH units), but returned to control values by t=6 h. Plasma total CO2 (TCO2) followed the same pattern. Immunolabeled sections revealed that Na+/K+-ATPase and V-H+-ATPase were usually located in the same cells. Western blotting revealed that the abundance of both proteins remained unchanged in whole gill homogenates and in a fraction enriched in cell membranes 6 h after the injections. The second experimental series was to induce long-term alkalosis by serially injecting 6000 micromol kg(-1) NaHCO3 every 6 h for 24 h. Blood pH completely recovered from the base loads within 6 h after each injection. Moreover, plasma TCO2 was not elevated 3 h after the second infusion, suggesting that HCO3(-) secreting mechanisms had been upregulated by that time. Na+/K+-ATPase and V-H+-ATPase cellular localizations did not change in the 24 h base infusion protocol. Na+/K+-ATPase abundance was similar in gill homogenates from fish from both treatments. However, Na+/K+-ATPase abundance in the membrane fraction was significantly lower in BIH, while V-H+-ATPase was greater both in whole gill and membrane fractions. Our results suggest that differential insertion of V-H+-ATPase and Na+/K+-ATPase into the basolateral membrane is involved in recovering from alkalotic stress in hagfish.     

Kinetics of phosphorylation of Na+/K(+)-ATPase by protein kinase C

The kinetics of phosphorylation of an integral membrane enzyme, Na+/K(+)-ATPase, by calcium- and phospholipid-dependent protein kinase C (PKC) were characterized in vitro. The phosphorylation by PKC occurred on the catalytic alpha-subunit of Na+/K(+)-ATPase in preparations of purified enzyme from dog kidney and duck salt-gland and in preparations of duck salt-gland microsomes. The phosphorylation required calcium (Ka approximately 1.0 microM) and was stimulated by tumor-promoting phorbol ester (12-O-tetradecanoylphorbol 13-acetate) in the presence of a low concentration of calcium (0.1 microM). PKC phosphorylation of Na+/K(+)-ATPase was rapid and plateaued within 30 min. The apparent Km of PKC for Na+/K(+)-ATPase as a substrate was 0.5 microM for dog kidney enzyme and 0.3 microM for duck salt-gland enzyme. Apparent substrate inhibition of PKC activity was observed at concentrations of purified salt-gland Na+/K(+)-ATPase greater than 1.0 microM. Phosphorylation of purified kidney and salt-gland Na+/K+ ATPases occurred at both serine and threonine residues. The 32P-phosphopeptide pattern on 15% sodium dodecyl sulfate-polyacrylamide gel electrophoresis after hydroxylamine cleavage of pure 32P-phosphorylated alpha subunit was the same for the two sources of enzyme, which suggests that the phosphorylation sites are similar. The results indicate that Na+/K(+)-ATPase may serve as a substrate for PKC phosphorylation in intact cells and that the Na+/K(+)-ATPase could be a useful in vitro model substrate for PKC interaction with integral membrane proteins.     

Simultaneous phosphorylation of Ser11 and Ser18 in the alpha-subunit promotes the recruitment of Na(+),K(+)-ATPase molecules to the plasma membrane

Renal sodium homeostasis is a major determinant of blood pressure and is regulated by several natriuretic and antinatriuretic hormones. These hormones, acting through intracellular second messengers, either activate or inhibit proximal tubule Na(+),K(+)-ATPase. We have shown previously that phorbol ester (PMA) stimulation of endogenous PKC leads to activation of Na(+),K(+)-ATPase in cultured proximal tubule cells (OK cells) expressing the rodent Na(+), K(+)-ATPase alpha-subunit. We have now demonstrated that the treatment with PMA leads to an increased amount of Na(+),K(+)-ATPase molecules in the plasmalemma, which is proportional to the increased enzyme activity. Colchicine, dinitrophenol, and potassium cyanide prevented the PMA-dependent stimulation of activity without affecting the increased level of phosphorylation of the Na(+), K(+)-ATPase alpha-subunit. This suggests that phosphorylation does not directly stimulate Na(+),K(+)-ATPase activity; instead, phosphorylation may be the triggering mechanism for recruitment of Na(+),K(+)-ATPase molecules to the plasma membrane. Transfected cells expressing either an S11A or S18A mutant had the same basal Na(+),K(+)-ATPase activity as cells expressing the wild-type rodent alpha-subunit, but PMA stimulation of Na(+),K(+)-ATPase activity was completely abolished in either mutant. PMA treatment led to phosphorylation of the alpha-subunit by stimulation of PKC-beta, and the extent of this phosphorylation was greatly reduced in the S11A and S18A mutants. These results indicate that both Ser11 and Ser18 of the alpha-subunit are essential for PMA stimulation of Na(+), K(+)-ATPase activity, and that these amino acids are phosphorylated during this process. The results presented here support the hypothesis that PMA regulation of Na(+),K(+)-ATPase is the result of an increased number of Na(+),K(+)-ATPase molecules in the plasma membrane.     

K+-Phosphatase activity of gill (Na+, K+)-ATPase from the blue crab, Callinectes danae: low-salinity acclimation and expression of the alpha-subunit

The kinetic properties of a microsomal gill (Na(+), K(+)) ATPase from the blue crab, Callinectes danae, acclimated to 15 per thousand salinity for 10 days, were analyzed using the substrate p-nitrophenylphosphate. The (Na(+), K(+))-ATPase hydrolyzed the substrate obeying Michaelian kinetics at a rate of V=102.9+/-4.3 U.mg(-1) with K(0.5)=1.7+/-0.1 mmol.L(-1), while stimulation by magnesium (V=93.7+/-2.3 U.mg(-1); K(0.5)=1.40+/-0.03 mmol.L(-1)) and potassium ions (V=94.9+/-3.5 U.mg(-1); K(0.5)=2.9+/-0.1 mmol.L(-1)) was cooperative. K(+)-phosphatase activity was also stimulated by ammonium ions to a rate of V=106.2+/-2.2 U. mg(-1) with K(0.5)=9.8+/-0.2 mmol.L(-1), following cooperative kinetics (n(H)=2.9). However, K(+)-phosphatase activity was not stimulated further by K(+) plus NH(4) (+) ions. Sodium ions (K(I)=22.7+/-1.7 mmol.L(-1)), and orthovanadate (K(I)=28.1+/-1.4 nmol.L(-1)) completely inhibited PNPPase activity while ouabain inhibition reached almost 75% (K(I)=142.0+/-7.1 micromol.L(-1)). Western blotting analysis revealed increased expression of the (Na(+), K(+))-ATPase alpha-subunit in crabs acclimated to 15 per thousand salinity compared to those acclimated to 33 per thousand salinity. The increase in (Na(+), K(+))-ATPase activity in C. danae gill tissue in response to low-salinity acclimation apparently derives from the increased expression of the (Na(+), K( (+) ))-ATPase alpha-subunit; phosphate-hydrolyzing enzymes other than (Na(+), K(+))-ATPase are also expressed. These findings allow a better understanding of the kinetic behavior of the enzymes that underlie the osmoregulatory mechanisms of euryhaline crustaceans.     

Chimeric domain analysis of the compatibility between H(+), K(+)-ATPase and Na(+),K(+)-ATPase beta-subunits for the functional expression of gastric H(+),K(+)-ATPase.

Gastric H(+),K(+)-ATPase consists of alpha-subunit with 10 transmembrane domains and beta-subunit with a single transmembrane domain. We constructed cDNAs encoding chimeric beta-subunits between the gastric H(+),K(+)-ATPase and Na(+),K(+)-ATPase beta-subunits and co-transfected them with the H(+),K(+)-ATPase alpha-subunit cDNA in HEK-293 cells. A chimeric beta-subunit that consists of the cytoplasmic plus transmembrane domains of Na(+),K(+)-ATPase beta-subunit and the ectodomain of H(+),K(+)-ATPase beta-subunit assembled with the H(+),K(+)-ATPase alpha-subunit and expressed the K(+)-ATPase activity. Therefore, the whole cytoplasmic and transmembrane domains of H(+),K(+)-ATPase beta-subunit were replaced by those of Na(+),K(+)-ATPase beta-subunit without losing the enzyme activity. However, most parts of the ectodomain of H(+),K(+)-ATPase beta-subunit were not replaced by the corresponding domains of Na(+), K(+)-ATPase beta-subunit. Interestingly, the extracellular segment between Cys(152) and Cys(178), which contains the second disulfide bond, was exchangeable between H(+),K(+)-ATPase and Na(+), K(+)-ATPase, preserving the K(+)-ATPase activity intact. Furthermore, the K(+)-ATPase activity was preserved when the N-terminal first 4 amino acids ((67)DPYT(70)) in the ectodomain of H(+),K(+)-ATPase beta-subunit were replaced by the corresponding amino acids ((63)SDFE(66)) of Na(+),K(+)-ATPase beta-subunit. The ATPase activity was abolished, however, when 4 amino acids ((76)QLKS(79)) in the ectodomain of H(+),K(+)-ATPase beta-subunit were replaced by the counterpart ((72)RVAP(75)) of Na(+),K(+)-ATPase beta-subunit, indicating that this region is the most N-terminal one that discriminates the H(+),K(+)-ATPase beta-subunit from that of Na(+), K(+)-ATPase.     

Quantitative immunocytochemical localization of Na+,K+-ATPase in rat ciliary epithelial cells

Ultrastructural localization of Na+,K+-ATPase in rat ciliary epithelium was investigated quantitatively by the protein A-gold technique, using an affinity-purified antibody against the alpha-subunit of Na+,K+-ATPase. Immunoblot analysis showed that the antibody bound specifically to the alpha-subunit of Na+,K+-ATPase in the ciliary body. Gold particles were found mainly on the basolateral surfaces of both the pigmented epithelial (PE) and nonpigmented epithelial (NPE) cells with an approximately twofold higher labeling density in the PE cells. A few gold particles were also found on the apical and ciliary channel surfaces of the PE cells, whereas no significant binding was found on the apical surfaces of the NPE cells. The basolateral surfaces of PE and NPE cells are markedly infolded and are much greater in area than the apical surfaces. This means that Na+,K+-ATPase is almost exclusively located on the basolateral surfaces of both the NPE and PE cells. We suggest that the Na+,K+-ATPase of both the NPE and PE cells play an important role in the formation of aqueous humor.     

久效磷对美国红鱼鳃Na^＋／K^＋-ATP酶活性和超显微结构的影响

经不同试验浓度的久效磷(0．25、0．5、1．0和2．0mg·L^-1)处理美国红鱼4d后,分别对鱼鳃Na^+／K^+—ATP酶活性和氯细胞密度进行了测定和计数,并观察了鱼鳃组织显微结构和超微结构的变化。结果表明,低浓度久效磷(0．25mg·L^-1)处理可以诱导鱼鳃氯细胞大量增生,Na^+／K^+—ATP酶活性增强,随着试验浓度的增加,久效磷对鳃组织的损伤越来越重,Na^+／K^+—ATP酶活性逐渐降低;久效磷对鱼鳃显微结构的损伤表现为鳃小片上皮细胞水肿、脱离。鳃小片基部粘连。鳃小片上皮细胞角质化;超微结构变化主要为内质网、线粒体、微小管和核膜的水肿及部分溶解,这种损伤表现为由细胞膜到细胞核的动态过程。     

Site-specific antibody of (Na(+) + K(+))-ATPase augments cardiac myocyte contraction without inactivating enzyme activity.

(Na(+) + K(+))-ATPase regulates both excitability and contractility of the heart. Little is known about the molecular basis of the enzyme that underlies its cardiac regulatory functions. Here we demonstrate that the (833)KRQPRNPKTDKLVNE(847) region, which resides in the alpha-subunit of rat (Na(+) + K(+))-ATPase, directly participates in the regulation of cardiac contraction. A site-specific antibody (SSA95) against this peptide sequence markedly increased intracellular Ca(2+) transients and contraction (EC(50) = 11.4 nM) in intact rat heart cells without inactivating the (Na(+) + K(+))-ATPase. These novel findings establish the first link between a precise structural region of the (Na(+) + K(+))-ATPase and cardiac positive inotropy.     

Failure to up-regulate gill Na+,K+-ATPase alpha-subunit isoform alpha1b may limit seawater tolerance of land-locked Arctic char (Salvelinus alpinus)

Many populations of Arctic char (Salvelinus alpinus) are land-locked, physically separated from the ocean by natural barriers and unable to migrate to sea like anadromous populations. Previous studies which experimentally transferred land-locked Arctic char to seawater report high mortality rates due to osmoregulatory failure and an inability to up-regulate gill Na(+),K(+)-ATPase activity. This study examined the mRNA expression of two recently discovered alpha-subunit isoforms of gill Na(+)K(+)-ATPase (alpha1a and alpha1b) during seawater exposure of land-locked Arctic char. mRNA levels of these gill Na(+),K(+)-ATPasealpha-subunit isoforms were compared to Na(+),K(+)-ATPase activity and protein levels and related to osmoregulatory performance. Land-locked Arctic char were unable to regulate plasma osmolality following seawater exposure. Seawater exposure did not induce an increase in gill Na(+),K(+)-ATPase activity or protein levels. Na(+),K(+)-ATPase isoform alpha1a mRNA quickly decreased upon exposure to seawater, while isoform alpha1b levels were unchanged. These results suggest the inability of land-locked Arctic char to acclimate to seawater is due a failure to up-regulate gill Na(+),K(+)-ATPase activity which may be due to their inability to increase Na(+),K(+)-ATPase alpha1b mRNA expression.     

Immunolocalization of NA(+),K(+)-ATPase in the branchial cavity during the early development of the European lobster Homarus gammarus (Crustacea, Decapoda).

We examined the ontogeny of the osmoregulatory sites of the branchial cavity in embryonic and early postembryonic stages of the European lobster Homarus gammarus through transmission electron microscopy, immunofluorescence microscopy, and immunogold electron microscopy using a monoclonal antibody IgGalpha(5) raised against the avian alpha-subunit of the Na(+),K(+)-ATPase. In mid-late embryos, Na(+),K(+)-ATPase was located along the pleurites and within the epipodite buds. In late embryos just before hatching, the enzyme was confined to the epipodite epithelia. After hatching, slight differentiations of ionocytes occured in the epipodites of larval stages. Na(+),K(+)-ATPase was also located in the ionocytes of the epipodites of larvae exposed to seawater (35.%o) and to dilute seawater (22.1 %o). After metamorphosis, the inner-side branchiostegite epithelium appeared as an additional site of enzyme location in postlarvae held in dilute seawater. Within the ionocytes, Na(+),K(+)-ATPase was mostly located along the basolateral infoldings. These observations are discussed in relation to the physiological shift from osmoconforming larvae to slightly hyper-regulating (in dilute seawater) postmetamorphic stages. The acquisition of the ability to hyper-osmoregulate probably originates from the differentiation, on the epipodites and mainly along the branchiostegites, of ionocytes that are the site of ion pumping as evidenced by the location of Na(+),K(+)-ATPase.     

The Na+ pump and intracellular signaling mechanisms

The main properties of Na+ /K(+)-ATPase as a natural receptor for cardiotonic steroids have been discusses. Primary attention is focused on structural and functional differences between the alpha-subunit isoforms of Na+/K(+)-ATPase in different tissues. General information on the role of the Na pump in signaling cascades in kidney epithelial cells, cardiomyocytes and neurons is presented. The data obtained indicate that, in neurons, several alpha-isoforms of Na+/K(+)-ATPase possessing different sensitivity to ouabain may have different signaling functions.     

Gill Na(+), K(+)-ATPase in a series of hyper-regulating gammarid amphipods: enzyme characterisation and the effects of salinity acclimation

The enzyme Na(+), K(+)-ATPase was investigated in the gills of selected hyper-regulating gammarid amphipods. Gill Na(+), K(+)-ATPase was characterised with respect to the main cation and co-factor concentrations for the freshwater amphipod Gammarus pulex. The optimum cation and co-factor concentrations for maximal gill Na(+), K(+)-ATPase activity in G. pulex were 100mM Na(+), 15mM K(+), 15mM Mg(2+) and 5mM ATP, at pH 7.2. The effects of salinity acclimation on gill Na(+), K(+)-ATPase activity and haemolymph sodium concentrations was investigated in selected gammarid amphipods from different salinity environments. Maximal enzyme activity occurred in all gammarids when acclimated to the most dilute media. This maximal activity coincided with the largest sodium gradient between the haemolymph and the external media. As the haemolymph/medium sodium gradient decreased, a concomitant reduction in gill Na(+), K(+)-ATPase activity occurred. This implicates the involvement of gill Na(+), K(+)-ATPase in the active uptake of sodium from dilute media in hyper-regulating gammarids.     

Ultracytochemical location of Na(+)/K(+)-atpase activity and effect of high salinity acclimation in gill and renal epithelia of the freshwater shrimp Macrobrachium olfersii (Crustacea, Decapoda).

Accumulation sites of lead phosphate reaction product consequent to Na(+)/K(+)-ATPase activity in gill and renal epithelia of the freshwater shrimp Macrobrachium olfersii were located ultracytochemically by para-nitrophenyl-phosphate hydrolysis and lead precipitation, and quantified per unit membrane area and cytoplasmic volume. In shrimps in freshwater (<0.5 per thousand S, 20 mOsm/kg H(2)O, 0.7 mEq Na(+)/liter), numerous sites of electron-dense, Na(+)/K(+)-ATPase reaction product accumulation were demonstrated in the membrane invaginations of the mitochondria-rich, intralamellar septal cells (12.5 +/- 1.7 sites/microm(2) membrane, 179 +/- 22 sites/microm(3) cytoplasm, mean+/- SEM, N 相似文献   

Assembly of the alpha-subunit of Torpedo californica Na+/K(+)-ATPase with its pre-existing beta-subunit in Xenopus oocytes

The alpha- and beta-subunits of Torpedo californica Na+/K(+)-ATPase were expressed in turn in single oocytes by alternately microinjecting the specific mRNAs for the alpha- and beta-subunits. The mRNA first injected was degraded prior to the injection of the second mRNA by injecting the antisense oligonucleotide specific for the first mRNA. The pre-existing beta-subunit, which had been synthesized by injecting mRNA for the beta-subunit, could assemble with the alpha-subunit expressed later in the single oocytes and the resulting alpha beta complex acquired both ouabain-binding and Na+/K(+)-ATPase activities. On the other hand, formation of the alpha beta complex was not detected when the alpha-subunit was expressed first, followed by the beta-subunit. These data suggest that the beta-subunit acts as a receptor or a stabilizer for the alpha-subunit upon the biogenesis of Na+/K(+)-ATPase.