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Muscle Sodium, Potassium, and [³H]Ouabain Binding in Identical Twins, Discordant for Type 2 Diabetes¹

Departments of Clinical Biochemistry and Genetics (S.D., N.A.H.K.), Cardiology B (S.D.), and Endocrinology M (A.V.), Odense University Hospital, 5000 Odense C; and Steno Diabetes Center (A.V.), 2820 Gentofte, Denmark

Address all correspondence and requests for reprints to: Dr. M. Stig Djurhuus, Svanereden 2, 5270 Odense N, Denmark. E-mail: msd{at}dadlnet.dk

	Abstract

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A reduced functional capacity of the sodium (Na), potassium (K) pump might reduce energy expenditure, inducing obesity and type 2 diabetes. Consequently, the Na and K content and [³H]ouabain binding capacity of skeletal muscle were measured in 10 monozygotic twin pairs discordant for type 2 diabetes and in 10 obese controls. Muscle [³H]ouabain binding capacity was reduced by approximately 20% in type 2 diabetes. Removing the genetic component by looking at differences within twin pairs, the difference in waist/hip ratio was associated with the difference in [³H]ouabain binding (r = -0.85; P < 0.002). Except for the type 2 diabetic twins in the basal state, both basal and insulin-stimulated energy expenditure were associated with the muscle K/Na ratio in the twins. In controls, the 2-h plasma glucose concentration during an oral glucose tolerance test was associated with the change in both muscle and plasma K induced by a euglycemic, hyperinsulinemic clamp. In conclusion, environmental factors related to the waist/hip ratio reduce the muscle [³H]ouabain binding capacity in type 2 diabetes. Without proving causality, the muscle K/Na ratio is associated with energy expenditure in individuals genetically predisposed to the development of type 2 diabetes.

	Introduction

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BETWEEN 4–50% of basal energy expenditure is used to maintain physiological intracellular sodium (Na) and potassium (K) concentrations, depending upon the tissue studied (1). This energy expenditure is increased when Na,K-adenosine triphosphatase (Na,K-ATPase) is stimulated (1). ß-Blockers are known to inhibit Na,K-ATPase (2), and patients receiving ß-blocker treatment gain weight (3). Type 2 diabetes is associated with obesity. In animal experiments the concentration of Na,K-ATPase is decreased in skeletal muscle of diabetic animals when they are untreated, but is normalized (4) or increased above normal (5) when the animals are treated with insulin. Concerning patients with diabetes mellitus, both the concentration and the activity of Na,K-ATPase are decreased in erythrocytes from at least some patients (6, 7). In skeletal muscle from both type 1 and type 2 diabetic patients an increased Na,K-ATPase concentration has been found (5). In obese patients decreased Na,K-ATPase concentration (8) and activity (8, 9) have been described in erythrocytes. In obese, insulin-resistant patients an increased Na/K ratio has been found in skeletal muscles (10), indicating a reduced pumping capacity. In the same study a positive correlation was found between the skeletal muscle Na/K ratio and body mass index (BMI). It was therefore concluded, that the most important factor causing an alteration of the observed muscle Na/K ratio was obesity (10). The same group also found a decreased muscle K content in obese subjects and an increase in muscle K content with weight loss (11). One factor that stimulates the Na,K-ATPase is insulin. A defect in the ability of the Na,K-ATPase to be stimulated or a reduced concentration of the membrane-bound Na,K-ATPase could result in decreased energy expenditure and probably decreased glucose turnover. Physical activity increases the concentration of Na,K-ATPase in skeletal muscle cells (12, 13), and it reduces the risk of developing type 2 diabetes mellitus (14) and obesity. Theoretically, reduced Na,K-ATPase activity might be an important factor in the development of obesity and type 2 diabetes in accordance with the thrifty gene theory (15).

Obesity, predominantly as abdominal fat (waist/hip ratio), is a strong predictor of the development of type 2 diabetes (16, 17). However, in a recent population-based twin study, Poulsen and co-workers found no significant impact of genetics per se on the waist/hip ratio after correction for overall obesity as reflected by BMI (data submitted). Therefore, both genetic and nongenetic factors may be of importance in the development of abdominal obesity in man. The glucose tolerance of healthy individuals has been related to the K channel Kir6.2 (18), and K channels seem to be involved in insulin-mediated glucose transport in human skeletal muscle (19). The intake of Na seems to influence insulin sensitivity (20, 21) and, in accordance with the above, insulin resistance has been found to be related to increased red cell Na and decreased red cell K (22), consistent with decreased Na,K-ATPase activity (22). A way of measuring the Na,K-ATPase concentration in human muscle biopsy specimens is to measure the [³H]ouabain binding capacity.

The aim of the present study was to measure the Na and K content and the Na,K-ATPase concentration of skeletal muscle in identical twins discordant for type 2 diabetes, to determine whether any association exists between the Na,K-ATPase concentration and activity and energy expenditure, glucose turnover, and the accumulation of fat. Using a twin study design made it possible to identify an eventual familial component.

	Subjects and Methods

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Subjects

Twelve pairs of identical twins discordant for type 2 diabetes were identified, primarily through the Danish Twin Register. A detailed description of the selection of cases and their characteristics was previously presented (23). In short, questionnaires were sent to twin pairs born between 1918 and 1940 who were recorded as monozygotic. A total of 626 twin pairs were asked whether they suffered from diabetes and their age at diagnosis. Included were twin pairs in whom the diagnosis of type 2 diabetes was probably due to the diagnosis of diabetes after the age of 40 yr. After exclusion of patients with diabetes who were not suffering from type 2 diabetes, a total of 12 discordant twin pairs were found. Their clinical characteristics are presented in Table 1. In 2 of these twin pairs, no muscle biopsy specimens were available for analysis. The clinical characteristics of the remaining 10 pairs can be seen in Table 1. In 1 of these 10 twin pairs, not enough muscle biopsy specimen was obtained from the healthy twin after the infusion of insulin and glucose to measure muscle Na,K-ATPase concentration. One control subject was investigated in conjunction with each of the twin pairs. The clinical characteristics of these controls can be seen in Table 1. Plasma K concentrations were analyzed in all 12 twin pairs and their matched controls.

Five of the patients with type 2 diabetes were treated with sulfonylurea, two patients were treated with metformine, one patient was treated with insulin, and the rest of the patients were treated with diet alone. The study was approved by the regional ethical committee. Informed consent was obtained from the participants.

	Materials and Methods

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The study design was described in detail previously (23). Muscle [³H]ouabain binding capacity and K/Na ratio were used as surrogate measures for Na,K-ATPase activity. Energy expenditure, glucose uptake rate, and glucose oxidation rate were used as metabolic variables.

The subjects were studied after a 10-h overnight fast. The plasma glucose concentration was normalized in the twins with type 2 diabetes by the infusion of insulin. A baseline period lasting 120 min followed, at the end of which plasma sampling was performed four times at 10-min intervals. Then insulin (Actrapid, Novo-Nordisk, Bagsvaerd, Denmark) was infused for 180 min at a constant rate of 40 mU/m²·min in all subjects. The plasma glucose concentration was maintained constant at a euglycemic level using a variable glucose (180 g/L) infusion rate. Plasma sampling was performed four times at 10-min intervals during the last 30 min of this period. An oral glucose tolerance test was performed in all subjects.

Muscle biopsy specimens

At the end of the basal period and at the end of the infusion of insulin and glucose muscle biopsy specimens were obtained. Muscle electrolyte content and [³H]ouabain binding capacity were determined after freeze-drying and dissection as described in detail previously (25). In patients with type 2 diabetes the slope of the Scatchard plot was -70.5 [95% confidence interval (CI), -159.5 to 18.4]. This did not differ from the value found in healthy subjects (25). The twin pairs and their controls were measured in the same series, without knowledge of diabetic status.

Plasma K concentrations

Plasma K concentrations were determined by flame emission spectrophotometry as the mean of four determinations in the basal period and as the mean of four determinations during the last 30 min of the infusion of insulin and glucose.

Baseline and clamp insulin-stimulated metabolic variables

The methods used and the results obtained were described in detail previously (23, 24). Arterialized venous blood was obtained. Metabolic data were obtained using a flow-through canopy gas analyzer system (Deltatrac, Datex, Helsinki, Finland), and plasma glucose concentrations were determined using an automated glucose oxidase method (Glucose Analyzer 2, Beckman Coulter, Inc., Fullerton, CA). Oral glucose tolerance was based on the 2-h plasma glucose concentration after a standard 75-g oral glucose load. Fat-free mass was determined using the bioimpedance method.

Statistical analysis

Statistical analysis was performed using the SPSS/PC⁺ package (SPSS, Inc., Chicago, IL) (26). After assuring that a Gaussian distribution could not be rejected using the Kolmogorov-Smirnov test, all variables were examined for differences between groups and the effect of the infusion of insulin and glucose using ANOVA or repeated measures ANOVA as appropriate. Comparisons were made between controls and healthy twins, between controls and type 2 diabetic twins, and between healthy twins and type 2 diabetic twins. In the case of gender differences, the difference were taken into account. Relations between variables were evaluated using least square regression analysis. Differences between correlation coefficients were evaluated as described in the Geigy Scientific Tables (27), with a significance limit of c₂. P < 0.05 was considered significant.

	Results

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Metabolism

Energy expenditure in the 10 twin pairs from whom a biopsy specimen was collected did not differ from that in their paired healthy controls. However, the infusion of insulin and glucose increased energy expenditure in the 2 control groups, but led to a decrease in energy expenditure in the type 2 diabetic twin group (Table 2). Insulin-stimulated glucose uptake rates were highest in the healthy control group (Table 3). The infusion of insulin and glucose increased the glucose uptake rate in both twin groups, with the largest increase in the healthy twin group and the least increase in the type 2 diabetic twin group (Table 3). Glucose oxidation was lower in the type 2 diabetic twins than in the two control groups, which did not differ in glucose oxidation (Table 4). The infusion of insulin and glucose increased glucose oxidation, with the least increase in the type 2 diabetic twins (Table 4).

No difference was found between groups in muscle Na, K, or water content (Table 5), nor did the ratio between im K and Na differ between groups (Table 5). The infusion of insulin and glucose did not influence intracellular electrolyte or water content (Table 5). The infusion of insulin and glucose induced a 15% decrease in the plasma K concentration in all groups (P < 0.0005). Plasma K decreased from 4.1 mmol/L (95% CI, 4.0–4.3) to 3.4 mmol/L (95% CI, 3.3–3.5) in the control group, from 4.0 mmol/L (95% CI, 3.8–4.1) to 3.4 mmol/L (95% CI, 3.3–3.6) in the healthy twin group, and from 3.9 mmol/L (95% CI, 3.8–4.0) to 3.4 mmol/L (95% CI, 3.2–3.5) in the type 2 diabetic group (n = 12 in each group). The plasma K concentration was lower in the patients with type 2 diabetes than in the controls (P < 0.05).

The muscle [³H]ouabain binding capacity was reduced in patients with type 2 diabetes compared with control subjects (Table 5). The infusion of insulin and glucose did not affect muscle [³H]ouabain binding capacity (Table 5).

Associations between metabolic and electrolyte variables

In the group of healthy twins BMI correlated positively with the K/Na ratio in skeletal muscle (Table 6). In controls, the waist/hip ratio correlated positively with the K/Na ratio in skeletal muscle (Table 6). This relation was not statistically significant in the twin groups, as the 95% CIs were wide due to the small number of subjects (Table 6). However, looking at the difference in waist/hip ratio within twin pairs as a function of the difference in basal muscle [³H]ouabain binding capacity within twin pairs, a negative correlation was found (Fig. 1).

View larger version (19K): [in this window] [in a new window]   Figure 1. The difference in waist/hip ratio within twin pairs as a function of the difference in basal muscle [3H]ouabain binding capacity within twin pairs. The plotted values are the type 2 diabetic twin values minus those for the healthy twin.

	Discussion

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A decreased Na,K-ATPase concentration in type 2 diabetes as found in this study might cause decreased energy consumption. Therefore, it seemed reasonable to determine whether any association exists between muscle [³H]ouabain binding capacity and the waist/hip ratio, which reflect visceral fat accumulation. Further, examining the actual values, one could get the impression that the healthy twins had a muscle [³H]ouabain binding capacity in between the [³H]ouabain binding capacity of healthy controls and that of the twins with type 2 diabetes, so a genetic component is not excluded by this study. However, the decrease in muscle [³H]ouabain binding capacity only reached statistical significance in the group of patients with type 2 diabetes, so a nongenetic component is likewise not excluded. Plotting the differences within twin pairs removes the genetic component in the variables in question. By doing so, it was found that the difference in muscle [³H]ouabain binding capacity within twin pairs was associated with the corresponding difference in waist/hip ratio, indicating that a nongenetic reduction of muscle [³H]ouabain binding capacity was associated with the development of abdominal obesity in type 2 diabetes mellitus. As the coefficient of correlation between muscle [³H]ouabain binding capacity and basal glucose oxidation in the healthy twin group was negative, part of the measured [³H]ouabain binding capacity might represent a compensatory mechanism that is exhausted when the genetically predisposed individual develops type 2 diabetes. This exhaustion seems to be associated with the accumulation of abdominal fat, as measured by the waist/hip ratio. No association was found between basal muscle [³H]ouabain binding capacity and BMI. The muscle Na,K-ATPase concentration in patients with type 2 diabetes has been reported previously in one study (5). This study reported an increased muscle [³H]ouabain binding capacity in patients with type 2 diabetes compared with healthy individuals. However, as noted by the researchers, the mean [³H]ouabain binding capacity in their control group was substantially lower than expected (5). The mean value actually observed was 223 pmol/g wet wt, which should be compared with a mean value of approximately 280 pmol/g wet wt for healthy individuals found in a series of studies by some of the same investigators (28, 29, 30, 31). It is therefore tempting to hypothesize that the reduced muscle [³H]ouabain binding capacity found in patients with type 2 diabetes in this study contributes to the development of reduced energy expenditure and the development of obesity and possibly hyperglycemia in these type 2 diabetic patients.

Myxoedema (29) and treatment with diuretics (30) are among the known conditions in which a reduction in skeletal muscle [³H]ouabain binding capacity has been found. ß-Blocker treatment inhibits catecholamine-induced stimulation of the Na,K pump (2). In these conditions, a reduction in glucose tolerance has been found (32, 33, 34, 35, 36), even though ß-blockers differ in this respect (35, 36, 37).

The concentration and activity of Na,K-ATPase constitute the ability of the cell to maintain a physiological equilibrium of electrolytes across the membrane. The ratio of the intracellular concentrations of K and Na might reflect this ability and could therefore to some extent express the activity of the Na,K-ATPase in vivo, even though the activity of ion channels might modify this ratio. The muscle K/Na ratio correlated positively with BMI in healthy twins and with the waist/hip ratio in controls. These relations are contrary to the positive correlation between the muscle Na/K ratio (the opposite ratio of that reported here) and BMI (10) and the decreased muscle K content in obese compared with lean subjects (11) found by Landin and co-workers, but the design was completely different. In the studies by Landin and co-workers, differences between groups were evaluated, whereas the relations between variables within each group were examined in the present study. As Landin and co-workers did find an increase in muscle K content after weight reduction in one study, it seems as if muscle K content relates negatively to BMI within the individual (11), even though the possibility of improved diet cannot be ruled out in the longitudinal study by Landin and co-workers (11).

The change in plasma K concentrations due to the infusion of insulin and glucose correlated negatively with the 2-h plasma glucose concentration during an oral glucose tolerance test in the healthy control group, but not in the two twin groups. Likewise, there was a linear relation between the change in muscle K content and the 2-h plasma glucose concentration in the control group, but not in the two twin groups. As the span of glucose values was larger in the two twin groups, this relation should have appeared in the twin groups if it did exist. This indicates an interrelation between glucose transport and the transport of K in healthy individuals, and that this interrelation is compromised in subjects predisposed to the development of type 2 diabetes. No one else has investigated the relation between glucose utilization and muscle K content in type 2 diabetic patients, but a K channel situated in the cell membrane of skeletal muscle has been shown to participate in the regulation of glucose tolerance (18, 19). Hansen et al. (18) showed that genetic polymorphism in the ATP-dependent K-channel Kir6.2 contributes to the variations in insulin sensitivity in humans. In an interventional study Wasada et al. demonstrated that K channels are involved in insulin-mediated glucose transport in human skeletal muscle (19).

As an association was found between the change in the plasma K concentration and the 2-h plasma glucose concentration during the oral glucose tolerance test, it seemed interesting to examine the associations among muscle K/Na ratio, energy expenditure, and glucose oxidation. This revealed differences in energy metabolism between subjects who are predisposed to the development of type 2 diabetes and patients with type 2 diabetes, on the one hand, and subjects without any predisposition, on the other, dependent upon the im K/Na ratio. Apart from a single coefficient of correlation that did not reach statistical significance, a negative coefficient of correlation was found between total energy expenditure and muscle K/Na ratio in subjects predisposed to the development of type 2 diabetes or with frank type 2 diabetes. This might indicate that the maintenance of a normal intracellular electrolyte content consumes a significant amount of energy in diabetic patients and in individuals predisposed to the development of diabetes, but not in controls. Therefore, we cannot exclude the possibility that alterations in the pumping activity of Na,K-ATPase might represent an underlying genetic abnormality contributing to the development of obesity and type 2 diabetes mellitus.

A few associations were found between glucose oxidation and surrogate measures of Na,K-ATPase activity. However, no consistent pattern was found, so the associations might be spurious findings, or the nonsignificant associations could be type 2 errors.

As the number of observations is very small, the risk of making a type 2 error is relatively large, so all nonsignificant results should be regarded with some skepticism. However, this was the number of subjects that was obtainable in a country with 5 million inhabitants. Nevertheless, the risk of making type 1 errors is still the usual 5%.

Overall, no differences in muscle electrolyte content were found among the groups, but the plasma K concentration differed between type 2 diabetic patients and control subjects.

The present study points toward an association between electrolyte derangements and the development of type 2 diabetes, at least in some patients. The K/Na ratio especially seems to be a genetically determined factor associated with energy expenditure, whereas a decrease in skeletal muscle [³H]ouabain binding capacity in patients with type 2 diabetes seems to be associated with environmental factors, to some extent related to the accumulation of visceral fat. In individuals without a genetic predisposition to type 2 diabetes, glucose tolerance is associated with the flux of K across the cell membrane, an association that was not found in subjects predisposed to the development of type 2 diabetes mellitus.

	Acknowledgments

 
We acknowledge the excellent technical assistance of Dorte Svensson.

	Footnotes

 
¹ This work was supported by grants from The Foundation of 1870, the Danish Diabetes Association, the Th. Maigaards and Mrs. Lilly Benthine Lunds Foundation, the Bernhard and Marie Kleins Foundation for Diabetes Research, the Clinical Research Institute, Odense University Hospital, the Danish Medical Associations Research Foundation, the Kathrine and Vigo Skovgaards Foundation, and the Engineer K. A. Rohdes and Wife’s Foundation.

Received March 1, 2000.

Revised September 11, 2000.

Accepted October 23, 2000.

	References

Top Abstract Introduction Subjects and Methods Materials and Methods Results Discussion References

 

1. Clausen T, van Hardeveld C, Everts ME. 1991 Significance of cation transport in control of energy metabolism and thermogenesis. Physiol Rev. 71:733–774.[Free Full Text]
2. Clausen T. 1998 Clinical and therapeutic significance of the Na⁺,K⁺ pump. Clin Sci. 95:3–17.[Medline]
3. Rössner S, Taylor CL, Byington RP, Furberg CD. 1990 Long term propranolol treatment and changes in body weight after myocardial infarction. Br Med J. 300:902–903.
4. Kjeldsen K, Brændgaard H, Sidenius P, Larsen JS, Nørgaard A. 1987 Diabetes decreases Na⁺-K⁺ pump concentration in skeletal muscles, heart ventricular muscle, and peripheral nerves of rat. Diabetes. 36:842–848.[Abstract]
5. Schmidt TA, Hasselbalch S, Farrell PA, Vestergaard H, Kjeldsen K. 1994 Human and rodent muscle Na⁺-K⁺-ATPase in diabetes related to insulin, starvation, and training. J Appl Physiol. 76:2140–2146.[Abstract/Free Full Text]
6. Vague P, Dufayet D, Coste T, Moriscot C, Jannot MF, Raccah D. 1997 Association of diabetic neuropathy with Na/K ATPase gene polymorphism. Diabetologia. 40:506–511.[CrossRef][Medline]
7. Mimura M, Makino H, Kanatsuka A, Asai T, Yoshida S. 1994 Reduction of erythrocyte (Na⁺-K⁺)ATPase activity in type 2 (non-insulin-dependent) diabetic patients with microalbuminuria. Horm Metab Res. 26:33–38.[Medline]
8. De Luise M, Blackburn GL, Flier JS. 1980 Reduced activity of the red-cell sodium-potassium pump in human obesity. N Engl J Med. 303:1017–1022.[Abstract]
9. Dianzani I, Boero R, Guarena C, et al. 1988 Abnormalities of sodium transport by sodium,potassium-activated adenosine triphosphatase in erythrocytes from obese children. Clin Sci. 74:57–61.[Medline]
10. Landin K, Lindgårde F, Saltin B, Smith U. 1991 The skeletal muscle Na:K ratio is not increased in hypertension: evidence for the importance of obesity and glucose intolerance. J Hypertens. 9:65–69.[CrossRef][Medline]
11. Landin K, Lindgarde F, Saltin B. 1989 Skeletal muscle potassium increases after diet and weight reduction in obese subjects with normal and impaired glucose tolerance. Acta Endocrinol (Copenh). 121:21–26.[Abstract/Free Full Text]
12. Madsen K, Franch J, Clausen T. 1994 Effects of intensified endurance training on the concentration of Na,K-ATPase and Ca-ATPase in human skeletal muscle. Acta Physiol Scand. 150:251–258.[Medline]
13. McKenna MJ, Schmidt TA, Hargreaves M, Cameron L, Skinner SL, Kjeldsen K. 1993 Sprint training increases human skeletal muscle Na⁺-K⁺-ATPase concentration and improves K⁺ regulation. J Appl Physiol. 75:173–180.[Abstract/Free Full Text]
14. Pan XR, Li GW, Hu YH, et al. 1997 Effects of diet and exercise in preventing NIDDM in people with impaired glucose tolerance. The Da Qing IGT and Diabetes Study. Diabetes Care. 20:537–544.[Abstract]
15. Sharma AM. 1998 The thrifty-genotype hypothesis and its implications for the study of complex genetic disorders in man. J Mol Med. 76:568–571.[CrossRef][Medline]
16. Ohlson LO, Larsson B, Bjorntorp P, et al. 1988 Risk factors for type 2 (non-insulin-dependent) diabetes mellitus. Thirteen and one-half years of follow-up of the participants in a study of Swedish men born in 1913. Diabetologia. 31:798–805.[Medline]
17. Lehtovirta M, Kaprio J, Forsblom C, Eriksson J, Tuomilehto J, Groop L. 2000 Insulin sensitivity and insulin secretion in monozygotic and dizygotic twins. Diabetologia. 43:285–293.[CrossRef][Medline]
18. Hansen L, Echwald SM, Hansen T, Urhammer SA, Clausen JO, Pedersen O. 1997 Amino acid polymorphisms in the ATP-regulatable inward rectifier Kir6.2 and their relationships to glucose- and tolbutamide-induced insulin secretion, the insulin sensitivity index, and NIDDM. Diabetes. 46:508–512.[Abstract]
19. Wasada T, Watanabe C, Nakagami T, Iwamoto Y. 1999 Adenosine triphosphate-sensitive potassium channels are involved in insulin-mediated glucose transport in humans. Metabolism. 48:432–436.[CrossRef][Medline]
20. Donovan DS, Solomon CG, Seely EW, Williams GH, Simonson DC. 1993 Effect of sodium intake on insulin sensitivity. Am J Physiol. 264:E730–E734.
21. Sharma AM, Ruland K, Spies KP, Distler A. 1991 Salt sensitivity in young normotensive subjects is associated with a hyperinsulinemic response to oral glucose. J Hypertens. 9:329–335.[CrossRef][Medline]
22. Modan M, Halkin H, Almog S, et al. 1985 Hyperinsulinemia: a link between hypertension, obesity and glucose intolerance. J Clin Invest. 75:809–817.
23. Vaag A, Henriksen JE, Madsbad S, Holm N, Beck-Nielsen H. 1995 Insulin secretion, insulin action, and hepatic glucose production in identical twins discordant for non-insulin-dependent diabetes mellitus. J Clin Invest. 95:690–698.
24. Vaag A, Alford F, Beck-Nielsen H. 1996 Intracellular glucose and fat metabolism in identical twins discordant for non-insulin-dependent diabetes mellitus (NIDDM): acquired versus genetic metabolic defects? Diabet Med. 13:806–815.[CrossRef][Medline]
25. Djurhuus MS, Klitgaard NAH, Tveskov C, et al. 1998 Methodological aspects of measuring human skeletal muscle electrolyte content and ouabain binding capacity. Anal Biochem. 260:218–222.[CrossRef][Medline]
26. Norusis MJ. 1990 SPSS/PC⁺, version 4.0. Chicago: SPSS, Inc.
27. Ciba-Geigy. 1982. Mathematical formulae. In: Lentner C, ed. Geigy scientific tables. Basel: Ciba-Geigy; vol 2:215–216.
28. Nørgaard A, Kjeldsen K, Clausen T. 1984 A method for the determination of the total number of 3H-ouabain binding sites in biopsies of human skeletal muscle. Scand J Clin Lab Invest. 44:509–518.[Medline]
29. Kjeldsen K, Nørgaard A, Gøtzsche CO, Thomassen A, Clausen T. 1984 Effect of thyroid function on number of Na-K pumps in human skeletal muscle. Lancet. 2:8–10.[CrossRef][Medline]
30. Dørup I, Skajaa K, Clausen T, Kjeldsen K. 1988 Reduced concentrations of potassium:magnesium, and sodium-potassium pumps in human skeletal muscle during treatment with diuretics. Br Med J. 296:455–458.
31. Clausen T. 1996 The Na⁺,K⁺ pump in skeletal muscle: quantification, regulation and functional significance. Acta Physiol Scand. 156:227–235.[CrossRef][Medline]
32. Teuscher AU, Weidmann PU. 1997 Requirements for antihypertensive therapy in diabetic patients: metabolic aspects. J Hypertens. 15(Suppl 2):S67–S75.
33. Andreani D, Menzinger G, Fallucca F, Aliberti G, Tamburrano G, Cassano C. 1970 Insulin levels in thyrotoxicosis and primary myxoedema: response to intravenous glucose and glucagon. Diabetologia. 6:1–7.[CrossRef][Medline]
34. West TET, Owens D, Sönksen PH, Srivastava MC, Tompkins CV, Nabarro JDN. 1975 Metabolic responses to monocomponent human insulin infusions in normal subjects and patients with liver and endocrine disease. Clin Endocrinol (Oxf). 4:573–584.[Medline]
35. Giugliano D, Acampora R, Marfella R, et al. 1997 Metabolic and cardiovascular effects of carvedilol and atenolol in non-insulin-dependent diabetes mellitus and hypertension. A randomized, controlled trial. Ann Intern Med. 126:955–959.[Abstract/Free Full Text]
36. Mediratta S, Fozailoff A, Frishman WH. 1995 Insulin resistance in systemic hypertension: Pharmacotherapeutic implications. J Clin Pharmacol. 35:943–956.[Abstract]
37. Malminiemi K, Lahtela J, Malminiemi O, Ala-Kaila K, Huupponen R. 1998 Insulin sensitivity in a long-term crossover trial with celiprolol and other antihypertensive agents. J Cardiovasc Pharmacol. 31:140–145.[CrossRef][Medline]

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