ARTICLE |
Correspondence to: Souad Sennoune, Laboratoire de Biochimie Fondamentale, Moléculaire et Clinique, Faculté de Pharmacie, 27 Bd J. Moulin, 13385 Marseille Cedex 5, France.
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Summary |
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Because diabetes causes alterations in hepatic membrane fatty acid content, these changes may affect the Na+,K+-ATPase. In this study we documented the effects of streptozotocin (STZ)-induced diabetes on hepatic Na+,K+-ATPase catalytic 1-subunit and evaluated whether these changes could be normalized by fish oil supplementation. Two groups of diabetic rats received fish oil or olive oil supplementation. Both groups had a respective control group. We studied the localization of catalytic
1-subunit on bile canalicular and basolateral membranes using immunocytochemical methods and confocal laser scanning microscopy, and the Na+,K+-ATPase activity, membrane fluidity, and fatty acid composition on isolated hepatic membranes. A decrease in the
1-subunit was observed with diabetes in the bile canalicular membranes, without changes in basolateral membranes. This decrease was partially prevented by dietary fish oil. Diabetes induces significant changes as documented by enzymatic Na+,K+-ATPase activity, membrane fluidity, and fatty acid content, whereas little change in these parameters was observed after a fish oil diet. In conclusion, STZ-induced diabetes appears to modify bile canalicular membrane integrity and dietary fish oil partly prevents the diabetes-induced alterations. (J Histochem Cytochem 47:809816, 1999)
Key Words:
Na+,K+-ATPase, catalytic 1-subunit, diabetes mellitus, fish oil, hepatocyte, confocal laser scanning microscopy, image analysis, fatty acid, membrane fluidity
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Introduction |
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The sodium pump, or Na+,K+-ATPase, is a ubiquitous plasma membrane-bound enzyme complex that plays a fundamental role in cellular function. Na+,K+-ATPase is assumed to consist of two subunits ( and ß) and a large lipid core (
-subunit, a polypeptide, exists in at least three isoforms and is responsible for coupling ATP hydrolysis with Na+, K+ transport across the membrane (
1-isoform (
-subunit antigenic determinants, has been reported for hepatocytes (
1-subunit was localized in BCM and BMs from rat and human hepatocytes.
Among various changes induced by diabetes on Na+,K+-ATPase in different tissues, alterations in lipid composition and the physical state of liver microsomal membranes have been shown (1-subunit expression that has been shown to be decreased or increased by diabetes depending on the organ (
1-subunit using immunocytochemical methods and confocal laser scanning microscopy in diabetic and nondiabetic control rat hepatocytes and quantified the staining with an image analysis method. We checked the effects of STZ-induced diabetes by measuring the Na+,K+-ATPase membrane activity, membrane fluidity, and fatty acid content. We then evaluated the effect of a fish oil (n-3 fatty acids) diet on these parameters.
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Materials and Methods |
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Animals
Five-week-old male SpragueDawley rats weighing approximately 200 g were randomly divided into four groups of six each. In two groups, diabetes was induced by IV injection of streptozotocin (STZ) at 60 mg/kg (Sigma; L'Isle d'Abeau, Chesne, France) diluted immediately before injection in citric acid buffer (0.01 mol/liter, pH 5.5). One group of diabetic animals (DM) was fed the standard rat chow diet supplemented with n-3 fatty acid-enriched fish oil concentrate (MaxEPA; Pierre Fabre Santé, Castres, France) administered over 8 weeks at a daily dose of 0.5 g/kg by gavage. This supplement is rich in eicosapentaenoic acid [EPA, C20:5 (n-3)] and docosahexenoic acid [DHA, C22:6 (n-3)]. The other group of diabetic animals (DO) was fed a standard rat chow diet supplemented with olive oil. The rats were fed with fish oil or olive oil after induction of diabetes with STZ. Diabetic rats were not treated with insulin. The nondiabetic control groups were also fed a standard rat chow diet supplemented with olive oil (CO) or with n-3 fatty acid-enriched fish oil (CM). Olive oil was chosen as the placebo because it does not contain n-3 fatty acids. Water was given ad libitum to all groups. All animal treatments adhered strictly to all institutional and national ethical guidelines. Blood samples were collected regularly from the tip of the tail, and blood glucose was measured with a reagent strip (Reflolux; Boehringer Mannheim, Mannheim, Germany). The results confirmed that all rats treated with STZ were diabetic. After 8 weeks, at the age of 13 weeks, animals were sacrificed by decapitation. The mean body weights were measured before IV injection of STZ and at the end of the study (Table 1). After 8 weeks of STZ treatment, body weight gain of diabetic animals (DO, DM) was greatly reduced compared with that of control animals (CO, CM).
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Immunocytochemical Analysis
Liver specimens were obtained immediately after death, rapidly rinsed with ice-cold physiological serum for less than 30 sec, frozen in liquid nitrogen, and stored at -80C until required. Samples of liver were cut into 5-µm sections at -20C using a cryostat. Liver sections were dried, fixed with 100% acetone for 10 min at 4C, and rapidly rehydrated in PBS, pH 7.2, for 2 min. Unspecific binding sites were blocked for 10 min at 37C with undiluted normal goat serum (Immunotech; Marseille, France). Liver sections were then incubated for 2 h at 37C with the primary antibody, a rabbit polyclonal antibody F against the Na+,K+-ATPase 1-subunit, provided by Dr E. Feraille (Nephrology Laboratory, Hôpital Cantonal; Geneve, Switzerland), diluted 1:100 in PBS and 2% bovine serum albumin (BSA) (Sigma; Saint-Quentin Fallavier, France). The sections were washed twice with PBS (5 min each) and incubated for 1 hr at room temperature (RT) with the secondary antibody, biotin-conjugated F(ab')2 fragment goat anti-rabbit IgG (H+L) (ref. O830; Immunotech) diluted 1:50 in PBS and 2% BSA. Sections were then washed twice with PBS (5 min each) and treated for 1 hr at RT with streptavidinfluorescein (ref. 0307) diluted 1:50 in PBS, and mounted in aqueous permanent mounting medium. For control experiments, in each case a slide was incubated with nonimmune rabbit serum (ref. HK117-5R; BioGenex, San Ramon, CA) diluted 1:100 in PBS, instead of anti
1-subunit antibody. The rabbit polyclonal antibody F against the Na+,K+-ATPase
1-subunit was evaluated for its isoform specificity by Western blotting with cerebral and kidney membranes (not shown). The sections were observed with a confocal laser scanning microscope (Leica; Heidelberg, Germany) with a x40 objective. Immunolocalization of hepatic
1-subunit in control and diabetic groups is shown in Figure 1A, Figure 1B, Figure 2A, and Figure 2B.
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Image Processing Analysis
Images were transferred to an IBM-compatible computer by real-time digitization of the video output of the confocal microscope with a PC Vision + card (Imaging Technology; Bedford, MA) allowing 8-bit accuracy (i.e., 256 gray levels). The linearity of the acquisition was checked by digitizing artificial images constructed with the confocal microscope computer and spanning the entire range of intensities (
Liver Plasma Membrane Isolation
Livers were removed, rapidly rinsed with ice-cold physiological saline for less than 30 sec, frozen in liquid nitrogen, and stored at -80C until required. Frozen pieces of liver (300 mg) were homogenized directly in ice-cold buffer containing 8% saccharose, 0.1 mM phenylmethane sulfonyl fluoride, 1 mM EDTA, and 30 mM imidazol-HCl, pH 7.4, at 25C with a polytron PT 10 (20 sec, setting 5) (
Enzyme Activity Measurements
Na+,K+-ATPase was determined using the coupled assay method as previously described (
Membrane Fluidity
The hepatocyte membranes were labeled with DPH (diphenylhexatriene), a fluorescent probe (Sigma) known to enter cell membranes, by incubating equal volumes of a hepatocyte suspension containing 100 µg/ml protein in phosphate buffer (5 mM NaH2Po4), 5 mM KCl, 145 mM NaCl, pH 7.4, and 2 µM DPH suspension in the same buffer. The DPH suspension was prepared just before use by vigorous shaking from a 2 mM stock solution in dimethylformamide. Incubation lasted for 30 min at 37C, with gentle stirring in the dark. Fluorescence measurements were performed at 37C. Fluorescence polarization (p) and anisotropy (r) measurements were done on a model SLM 4800 polarization spectrofluorometer as described previously (
Fatty Acid Composition
Membrane lipids were extracted with methanol and chloroform according to the method of
Statistical Analysis
All results are expressed as mean ± SE. Results of immunocytochemical quantitative analysis were performed by using analysis of variance (ANOVA). The significant differences were determined by Fisher's post hoc least significant difference test and the Scheffé F-test at a probability value of 95%. Statistical evaluation of other results utilized an ANOVA procedure with Tukey test for multiple comparisons of normal distributions and the KruskalWallis ANOVA with Dunn's test for multiple comparisons of nonparametric distributions (Sigmastat Statistical Software). Values of p<0.05 were considered statistically significant.
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Results |
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Plasma glucose levels of STZ-treated rats were significantly elevated (Table 1). Daily supplementation with fish oil at 0.5 g/kg had no effect on the hyperglycemia.
Immunocytochemical Qualitative Analysis
The 1-subunit was localized to the BM and the BCM in control (CO, CM) and diabetic (DO, DM) groups. BCM appeared as fluorescent spots in cross-sections. The BCM and BM Na+,K+-ATPase
1-subunit localization was maintained in experimental diabetes groups (Figure 2A and Figure 2B). In both diabetic groups, the staining was lower than in control groups at the level of bile canaliculi (Figure 2A and Figure 2B). The fluorescence intensity observed in the DO group was lower than in the DM group. All the control studies using nonimmune rabbit serum were entirely devoid of staining.
Immunocytochemical Quantitative Analysis
Confocal images were studied quantitatively by measuring the intensity of the staining of BCM and BM 1-subunit. Figure 3 and Figure 4 show the results of quantitative analysis performed on the BCM and BM Na+, K+-ATPase catalytic
1-subunit. Quantitative determination of bile canaliculi mean specific fluorescence (MSF) of control and diabetic rat hepatocytes revealed significant differences (Figure 3). Our qualitative results were corroborated by the comparison of MSF of diabetic groups to MSF of control groups, showing a significant decrease (p<0.05) in the staining of Na+, K+-ATPase
1-subunit. A decrease of 53% and 26% was observed in DO and DM groups, respectively. No significant differences of Na+,K+-ATPase
1-subunit between diabetic and control groups were observed in the BM (Figure 4). The n-3 fatty acid supplementation did not change the density of the catalytic subunit of Na+,K+-ATPase in control groups in either membrane. However, the decrease in bile canaliculi MSF observed in the DO group was partly prevented in the DM (DO vs DM, p<0.05). A significant restoration in the BCM by 27% was specifically associated to the n-3 fatty acid supplementation in the diabetic state. The changes induced by diabetes were limited to BCM. The BM was not modified by diabetes or by n-3 fatty acid supplementation.
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Liver Membrane Na+,K+-ATPase Activities
Figure 5 shows Na+,K+-ATPase activity in liver microsomal membranes from control (CO, CM) and diabetic rats (DO, DM). The enzyme activities were significantly increased by diabetes compared to their respective control groups (Figure 5). In STZ-induced diabetic rats, the Na+,K+-ATPase activity increased by 89% and 60%. Dietary fish oil (n-3 fatty acids) treatment had no effect on Na+,K+-ATPase activity. The activity in the CM and DM groups appeared higher than in the CO and DO groups, respectively (Figure 5), but the difference was not statistically significant.
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Liver Membrane Lipid Fluidity
The fluorescence polarization (p) and anisotropy (r) were measured. Polarization and anisotropy values were higher in both diabetic groups than in control groups (Table 2), indicating that the membranes from diabetic groups were less fluid than those from control groups. These results were significant only in the DO group relative to the CO group (p<0.05).
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Fatty Acid Composition of Liver Membranes
The composition of fatty acids in purified membranes from liver from rats with STZ-induced diabetes, with or without fish oil treatment, was determined and compared with that of the nondiabetic groups (Table 3).
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The effect of diabetes (CO vs DO) in rats was a significant decrease in palmitoleic [16:1 (n-7)], oleic [18:1 (n-9)], arachidonic [20:4 (n-6)] and eicosapentaenoic [EPA, C20:5 (n-3)] acids, whereas the percentage of linoleic [C18:2(n-6)] and docosahexenoic [DHA, C22:6 (n-3)] acids was increased. This effect was not significant for polyunsaturated fatty acid (PUFA) amounts, but the total amount of monounsaturated fatty acids (MUFA) decreased significantly.
The main effect of fish oil supplementation (CO vs CM) in rats was a significant decrease in [16:1 (n-7)] and [18:1(n-9)] fatty acids, whereas the percentage of [C18:2 (n-6)] fatty acid was significantly increased. This specific effect was not significant for PUFA, but the total amount of MUFA decreased significantly. After fish oil supplementation (DO vs DM) in diabetes, the [C18:2(n-6)] fatty acid levels decreased. No significant change in the percentage of oleic, arachidonic, and DHA fatty acids was observed, whereas the palmitoleic and EPA fatty acids levels increased significantly.
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Discussion |
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The purpose of our study was twofold: first, to localize the hepatic Na+,K+-ATPase catalytic 1-subunit, and then to determine the effects of STZ-induced diabetes. Our second aim was to evaluate the effects of dietary fish oil on these diabetes changes.
In agreement with previous functional and biochemical studies, we found that the catalytic subunit is located on the BCM as well as on the BM (1-subunit and the basolateral localization found in a number of biochemical and cytochemical studies (
1-subunit antibody could recognize similar epitopes in Ca++-ATPase (
To our knowledge, the localization of hepatic Na+,K+-ATPase in experimental diabetes has not been studied. This report confirms a basolateral and bile canalicular localization of Na+,K+-ATPase 1-subunit in control and diabetic groups. However, the decreased density of the Na+,K+-ATPase catalytic
1-subunit induced by diabetes was limited to the BCM. The basolateral localization of the
1-subunit remains the same between control and diabetic groups. In contrast, the present study demonstrates that STZ-induced diabetes increases enzymatic activity of liver membranes, whereas the abundance of the
1-subunit decreases in BCM. Future study will be required to explain these contradictory findings and to determine the factors involved in the change in enzyme activity. The fact that
1-subunit density does not fully account for the increase in enzyme activity suggests that alterations in the membrane environment may also play a role. The mechanism regulating bile canaliculi Na+, K+-ATPase in hepatocytes can be explained by the fact that diabetes is a chronic disorder that induces alterations in total fatty acid content and in the physical state of liver membranes. Alterations in membrane fluidity and fatty acid content remain possible mechanisms responsible for decreased
1-subunit. Polarization and anisotropy measurements on membranes from diabetic groups indicate that their lipid structure behaves rigidly. This decrease in
1-subunit density can be attributed to changes in membrane fluidity.
6- and
5-desaturase activity because final products of these enzymes were decreased by C20:4 (n-6) (arachidonic acid) and C20:5 (n-3) (EPA).
Concerning the mechanisms regulating bile canaliculi Na+,K+-ATPase in hepatocytes, we can speculate that the decreased 1-subunit density might be related to modification of fatty acid composition. This might alter the molecular configuration of the membrane, affecting the bound enzyme system and thus leading to the lowered activity, but this is not the case in our study. Diabetes is known to produce profound changes in hepatobiliary secretion. In the same experimental model of STZ-induced diabetes,
1-subunit is associated with changes in biliary secretion remains to be determined.
The purpose of this study was to assess the ability of dietary fish oil to prevent diabetes-induced changes. In this study, fish oil did not affect the Na+,K+-ATPase catalytic 1-subunit under control conditions. We did not observe significant differences between control groups, whereas the decrease observed in diabetes-induced changes was prevented to a small degree by dietary fish oil. Moreover, dietary fish oil had no effect on enzymatic activity. The trend observed in diabetic groups was not significant in the fish oil-treated groups. Dietary fish oil affects the fatty acid composition of the liver membrane and prevents the decrease of eicosapentaenoic acid observed with STZ-induced diabetes. These biochemical effects may alter membrane architecture and enzymatic activities (
In conclusion, this study demonstrates that Na+,K+-ATPase catalytic 1-subunit was altered in BCM by diabetes and was partly prevented by dietary fish oil, and suggests that fish oil therapy may be effective in preventing or treating some of the consequences of diabetes.
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Acknowledgments |
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We are grateful to A-M Benoliel for scientific assistance and to Pr P. Bongrand (Immunology laboratory, Hôpital Sainte-Marguerite, Marseille).
We thank Dr E. Feraille for providing the antibody (Nephrology Laboratory, Hôpital Cantonal, Geneve). We would also like to thank P. Micel for English assistance.
Received for publication December 1, 1998; accepted January 12, 1999.
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Literature Cited |
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![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
André P, Benoliel AM, Capo C, Foa C, Buferne M, Boyer C, SchmittVerhults AM, Bongrand P (1990) Use of conjugates made between a cytolytic T cell clone and target cells to study the distribution of membrane molecules in cell contact areas. J Cell Sci 97:335-347[Abstract]
Balasubramaniam S, Simons LA, Chang S, Hickie JB (1985) Reduction in plasma cholesterol and increase in biliary cholesterol by a diet rich in n-3 fatty acids in the rat. J Lipid Res 26:684-689[Abstract]
Barada K, Okolo C, Field M, Cortas N (1994) Na+,K+-ATPase in diabetic rat small intestine. Changes at protein and mRNA levels and role of glucagon. J Clin Invest 93:2725-2731[Medline]
Benkoël L, Benoliel AM, Brisse J, Sastre B, Bongrand P, Chamlian A (1995) Immunocytochemical study of Na+K+-ATPase 1 and ß1 subunits in human and rat normal hepatocytes using confocal microscopy. Cell Mol Biol 41:499-504
Bligh EG, Dyer WJ (1959) A rapid method of total lipid extraction and purification. Can J Biochem Physiol 37:911-917
Blitzer BL, Boyer JL (1978) Cytochemical localization of Na+K+-ATPase in the rat hepatocyte. J Clin Invest 62:1104-1108[Medline]
Blitzer BL, Boyer JL (1984) Localization of Na+K+-ATPase on the hepatocyte plasma membrane. Gastroenterology 87:1206-1207[Medline]
Boyer JL, Allen RM, Cheng Ng O (1983) Biochemical separation of Na+K+-ATPase from a "purified" light density, "canalicular"-enriched plasma membrane fraction from rat liver. Hepatology 3:18-28[Medline]
Brasitus IA, Davidson NO, Schachter D (1985) Variations in dietary triacylglycerol saturation alter the lipid composition and fluidity of rat intestinal plasma membranes. Biochim Biophys Acta 812:460-472[Medline]
Burwen SJ, Schmucker DL, Jones AL (1992) Subcellular and molecular mechanisms of bile secretion. Int Rev Cytol 135:269-313[Medline]
Chamlian A, Benkoël L, Chrestian J, Di CostanzoDufetel N, Cano N, Di Costanzo J (1988) Cytochemical localization of ouabain sensitive, K+-dependent p-nitrophenyl phosphatase in human liver. Its relationship to Na+K+-ATP-ase. Cell Mol Biol 34:215-222[Medline]
Chautan M, Dell'Amico M, Bourdeaux M, Leonardi J, Charbonnier M, Lafont H (1990) Lipid diet and enterocytes microsomal membrane fluidity in rats. Chem Phys Lipids 54:25-32[Medline]
Christon R, Fernandez Y, CambonGros C, Periquet A, Deltour P, Leger CL, Mitjavila S (1988) The effect of dietary essential fatty acid deficiency on the composition and properties of the liver microsomal membrane of rats. J Nutr 118:1311-1318[Medline]
Clandinin MT, Field CJ, Hargreaves K, Morson LA, Zsigmond E (1985) Role of diet fat in subcellular structure and function. Can J Physiol Pharmacol 63:546-556[Medline]
Dang AQ, Kemp K, Faas FH, Carter WJ (1989) Effects of dietary fats on fatty acid composition and delta 5 desaturase in normal and diabetic rats. Lipids 24:882-889[Medline]
Gerbi A, Barbey O, Raccah D, Coste T, Jamme I, Nouvelot A, Ouafik L, Lévy S, Vague P, Maixent JM (1997) Alteration of Na+,K+-ATPase isoenzymes in diabetic cardiomyopathy: effect of dietary supplementation with fish oil (n-3 fatty acids) in rats. Diabetologia 40:496-505[Medline]
Gerbi A, Debray M, Maixent J-M, Chanez C, Bourre J-M (1993a) Heterogeneous Na+ sensitivity of Na+,K+-ATPase isoenzymes in whole brain membranes. J Neurochem 60:246-252[Medline]
Gerbi A, Zérouga M, Debray M, Durand G, Chanez C, Bourre JM (1993b) Effect of dietary -linolenic acid on functional characteristics of Na+,K+-ATPase isoenzymes in whole brain membranes of weaned rats. Biochim Biophys Acta 1165:291-298[Medline]
Gerbi A, Zérouga M, Debray M, Durand G, Chanez C, Bourre JM (1994) Effect of fish oil diet on fatty acid composition of phospholipids of brain membranes and on kinetic properties of Na+,K+-ATPase isoenzymes of weaned and adult rats. J Neurochem 62:1560-1569[Medline]
Gorvel JP, Liaboeuf A, Massey K, Liot D, Goridis C, Maroux S (1983) Recognition of sodium- and potassium-dependent adenosine triphosphatase in organs of the mouse by means of a monoclonal antibody. Cell Tissue Res 234:619-632[Medline]
Hara T, Kudou M, Otake K, Hayashi T, Asano G (1988) Immunohistochemical localization of Na+,K+-ATPase in human liver. Acta Histochem Cytochem 21:593-599
Holman RT, Johnson SB, Gerrard JM, Mauer SM, KupchoSandberg S, Brown DM (1983) Arachidonic acid deficiency in streptozotocin-induced diabetes. Proc Natl Acad Sci USA 80:2375-2379[Abstract]
Kaplanski G, Farnarier C, Benoliel AM, Foa C, Kaplanski S, Bongrand P (1994) A novel role for E- and P-selectins: shape control of endothelial cell monolayers. J Cell Sci 107:2449-2457
Leffert HL, Schenk DB, Hubert JJ, Skelly H, Schumacher M, Ariyasu R, Ellisman M, Koch KS, Keller GA (1985) Hepatic Na+K+-ATPase: a current view of its structure, function and localization in rat liver as revealed by studies with monoclonal antibodies. Hepatology 5:501-507[Medline]
Lemas MV, Hamrick M, Takeyasu K, Fambrough DM (1994) 26 Amino acids of an extracellular domain of the Na+K+-ATPase -subunit are sufficient for assembly with the Na+K+-ATPase ß-subunit. J Biol Chem 269:8255-8259
Lenaz G (1987) Lipid fluidity and membrane protein dynamics. Biosci Rep 7:823-837[Medline]
Lingrel JB, Orlowski J, Shull MM, Price EM (1990) Molecular genetics of Na+K+-ATPase. Prog Nucleic Acid Res Mol Biol 38:37-89[Medline]
Lowry OH, Rosebrough NJ, Farr AL, Randall RJ (1951) Protein measurement with the Folin phenol reagent. J Biol Chem 193:265-275
Lu SC, Kuhlenkamp J, Wu H, Sun W-M, Stone L, Kaplowitz N (1997) Progressive defect in biliary GSH secretion in streptozotocin-induced diabetic rats. Am J Physiol 252:G374-382
Maixent J-M, Fenard S, Kawamoto RM (1991) Tissue localization of active Na+,K+-ATPase isoenzymes by determination of their profile of inhibition with ouabain, digoxin, digitoxigenin and cordil, a new aminosteroid cardiotonic. J Rec Res 11:687-698
Molitoris BA (1993) Na+,K+-ATPase that redistributes to apical membrane during ATP depletion remains functional. Am J Physiol 265:F693-697
Murphy MG (1990) Dietary fatty acids and membrane protein function. J Nutr Biochem 1:68-79
Ng Y-C, Tolerico PH, Book C-BS (1993) Alterations in levels of Na+,K+-ATPase isoforms in heart, skeletal muscle, and kidney of diabetic rats. Am J Physiol 265:E243-251
Ohta A, Mayo MC, Kramer N, Lands WEM (1990) Rapid analysis of fatty acids in plasma lipids. Lipids 25:742-747[Medline]
Paller MS (1994) Lateral mobility of Na+,K+-ATPase and membrane lipids in renal cells. Importance of cytoskeletal integrity. J Membr Biol 142:127-135[Medline]
Schenk DB, Hubert JJ, Leffert HL (1984) Use of a monoclonal antibody to quantify (Na+K+)-ATPase activity and sites in normal and regenerating rat liver. J Biol Chem 259:14941-14951
Schenk DB, Leffert HL (1983) Monoclonal antibodies to rat Na+,K+-ATPase block enzymatic activity. Proc Natl Acad Sci USA 80:5281-5285[Abstract]
Sellinger M, Barrett C, Malle P, Gordon ER, Boyer JL (1990) Cryptic Na+,K+-ATPase activity in rat liver canalicular plasma membranes: evidence for its basolateral origin. Hepatology 11:223-229[Medline]
Simon FR, Leffert HL, Ellisman M, Iwahashi M, Deerinck T, Fortune J, Morales D, Dahl R, Sutherland E (1995) Hepatic Na+,K+-ATPase enzyme activity correlates with polarised ß-subunit expression. Am J Physiol 269:C69-84
Simopoulos AR (1991) Omega-3 fatty acids in health and disease and in growth and development. Am J Clin Nutr 54:438-463[Abstract]
Smit MJ, Temmerman AM, Wolters H, Kuipers F, Beynen AC, Vonk RJ (1991) Dietary fish oil-induced changes in intrahepatic cholesterol transport and bile acid synthesis in rats. J Clin Invest 88:943-951[Medline]
Sutherland E, Dixon BS, Leffert HL, Skelly H, Zaccaro L, Simon FR (1988) Biochemical localization of hepatic surface-membrane Na+,K+-ATPase activity depends on membrane lipid fluidity. Proc Natl Acad Sci USA 85:8673-8677[Abstract]
Sztul ES, Biemesderfer D, Caplan MJ, Kashgarian M, Boyer JL (1987) Localization of Na+,K+-ATPase -subunit to the sinusoidal and lateral but not canalicular membranes of rat hepatocytes. J Cell Biol 104:1239-1248[Abstract]
Takemura S, Omori K, Tanaka K, Omori K, Matsuura S, Tashiro Y (1984) Quantitative immunoferritin localization of Na+,K+-ATPase on canine hepatocyte cell surface. J Cell Biol 99:1502-1510[Abstract]
Vasilets LA, Schwarz W (1994) The Na+K+ pump: structure and function of the alpha-subunit. Cell Physiol Biochem 4:81-95
Yamamoto K, Mayahara H, Ogawa K (1984) Cytochemical localization of ouabain-sensitive, K-dependent p-nitrophenylphosphatase in the rat hepatocyte. Acta Histochem Cytochem 17:23-35