Na+-K+-ATPase in rat skeletal muscle: content, isoform, and activity characteristics

2004 ◽  
Vol 96 (1) ◽  
pp. 316-326 ◽  
Author(s):  
J. R. Fowles ◽  
H. J. Green ◽  
J. Ouyang
Keyword(s):  
Atpase Activity ◽  
Fiber Type ◽  
Hydrolytic Activity ◽  
Ouabain Binding ◽  
Equal Distribution ◽  
Atpase Assay ◽  
Type Composition ◽  
Activity Measurements ◽  
Male Wistar Rats

The purpose of this study was to investigate the hypothesis that muscle Na+-K+-ATPase activity is directly related to Na+-K+-ATPase content and the content of the α2-catalytic isoform in muscles of different fiber-type composition. To investigate this hypothesis, tissue was sampled from soleus (Sol), red gastrocnemius (RG), white gastrocnemius (WG), and extensor digitorum longus (EDL) muscles at rest from 38 male Wistar rats weighing 413 ± 6.0 g (mean ± SE). Na+-K+-ATPase activity was determined in homogenates (Hom) and isolated crude membranes (CM) by the regenerating ouabain-inhibitable hydrolytic activity assay (ATPase) and the 3- O-methylfluorescein K+-stimulated phosphatase (3- O-MFPase) assay in vitro. In addition, Na+-K+-ATPase content (Bmax) and the distribution of α1-, α2-, β1-, and β2-isoforms were determined by [3H]ouabain binding and Western blot, respectively. For the ATPase assay, differences ( P < 0.05) in enzyme activity between muscles were observed in Hom (EDL > WG) and in CM (Sol > EDL = WG). For the 3- O-MFPase assay, differences ( P < 0.05) were also found for Hom (Sol > RG = EDL > WG) and CM (Sol = WG > RG). For Bmax, differences in the order of RG = EDL > Sol = WG ( P < 0.05) were observed. Isoform distribution was similar between Hom and CM and indicated in CM, a greater density ( P < 0.05) of α1 in Sol than WG and EDL ( P < 0.05), but more equal distribution of α2 between muscles. The β1 was greater ( P < 0.05) in Sol and RG, and the β2 was greater in EDL and WG ( P < 0.05). Over all muscles, the correlation ( r) between Hom 3- O-MFPase and Bmax was 0.45 ( P < 0.05) and between Hom α2 and Bmax, 0.59 ( P < 0.05). The α1 distribution correlated to Hom 3- O-MFPase ( r = 0.79, P < 0.05) CM ATPase ( r = 0.69, P < 0.005) and CM 3- O-MFPase activity ( r = 0.32, P < 0.05). The α2 distribution was not correlated with any of the Na+-K+-ATPase activity measurements. The results indicate generally poor relationships between activity and total pump content and α2 isoform content of the Na+-K+-ATPase. Several factors, including the type of preparation and the type of assay, appear important in this regard.

Preservation of sarcoplasmic reticulum Ca2+-sequestering function in homogenates of different fibre type composition following sprint activity

1994 ◽  
Vol 72 (10) ◽  
pp. 1231-1237 ◽  
Author(s):  
J. Dossett-Mercer ◽  
H. J. Green ◽  
E. Chin ◽  
F. Grange
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
Dry Weight ◽  
Muscle Fibre Types ◽  
Glycogen Depletion ◽  
Fibre Type Composition ◽  
Fibre Composition ◽  
Type Composition ◽  
Male Wistar Rats

To examine the effect of exercise on sarcoplasmic reticulum function in muscle tissue of different fibre composition, adult male Wistar rats weighing 388 ± 23 g (x ± SE) ran intermittently on a treadmill until fatigue. Fatigue was induced by 15–20 min of running performed at 52 m/min on an 8° incline in periods of 2.5 min of exercise separated by 2 min of recovery. Analysis of sarcoplasmic reticulum Ca2+ ATPase activity determined in homogenates indicated no difference (p > 0.05) between age-matched control and exercised tissue for the soleus (SOL; 0.121 ± 0.012 vs. 0.156 ± 0.018 μmol∙mg−1 protein∙min−1), red gastrocnemius (RG; 0.381 ± 0.022 vs. 0.354 ± 0.022), or white gastrocnemius (WG; 0.526 ± 0.05 vs. 0.471 ± 0.031). Similarly, both total ATPase and Mg2+ ATPase activities were unaffected by the exercise in any of the tissues examined. Exercise also failed to alter sarcoplasmic reticulum Ca2+ uptake in homogenates of the SOL (1.43 ± 0.15 vs. 1.38 ± 0.19 nmol∙mg−1 protein∙min−1), RG (3.74 ± 0.29 vs. 3.59 ± 0.24), and WG (5.98 ± 0.48 vs. 5.41 ± 0.50). At fatigue, glycogen depletion was similar in all tissue types and amounted to 65.1% in the SOL (172 ± 9 vs. 60 ± 16 mmol∙glucosyl units−1∙kg−1 dry weight), 74.4% in RG (164 ± 8 vs. 42 ± 6), and 79% in the WG (167 ± 9 vs. 35 ± 9). It is concluded that exercise by itself does not alter sarcoplasmic reticulum Ca2+-sequestering function in tissues of primarily different fibre composition when determined in homogenates in vitro. The integrity of sarcoplasmic reticulum function is preserved despite an apparent extensive recruitment of all tissue types during the exercise.Key words: sarcoplasmic reticulum function, Ca2+ uptake, Ca2+ ATPase activity, muscle fibre types.

In vitro O2 uptake and histochemical fiber type of resting hamster muscles

1984 ◽  
Vol 57 (1) ◽  
pp. 246-253 ◽  
Author(s):  
S. M. Sullivan ◽  
R. N. Pittman
Keyword(s):  
Surface Area ◽  
Fiber Type ◽  
Oxidative Capacity ◽  
Histochemical Staining ◽  
Striated Muscles ◽  
Type Composition ◽  
Slow Twitch ◽  
Pattern Number ◽  
Fast Twitch

In vitro oxygen consumption (VO2), histochemical fiber type, capillary arrangement, and muscle fiber geometry were measured in three hamster striated muscles. These muscles varied markedly in their histochemical fiber type composition (% by number): retractor (70% FG, fast-twitch, glycolytic; 16% FOG, fast-twitch, oxidative-glycolytic; 14% SO, slow-twitch, oxidative); soleus (57% FOG, 43% SO), and sartorius (98% FG, 2% FOG). Sartorius VO2 [0.80 +/- 0.034 (SE) ml O2 X min-1 X 100 g-1] was significantly different (P less than 0.01) from VO2 of retractor (0.89 +/- 0.038) and soleus (1.00 +/- 0.048).The number of capillaries around a fiber and the surface area/volume were greater for FOG and SO fibers than for FG fibers. Fibers of all types appeared to be roughly elliptical in shape. Capillaries were uniformly distributed around fibers in the soleus, but they were located more toward the ends of the major diameter in the retractor and sartorius. The results suggest a relationship among a fiber's oxidative capacity (based on its histochemical staining pattern), number of surrounding capillaries and surface area/volume. Furthermore, results suggest that VO2 and capillary spacing around a fiber may depend on fiber type.

Na+-K+-ATPase properties in rat heart and skeletal muscle 3 mo after coronary artery ligation

2005 ◽  
Vol 99 (2) ◽  
pp. 656-664 ◽  
Author(s):  
D. J. Barr ◽  
H. J. Green ◽  
D. S. Lounsbury ◽  
J. W. E. Rush ◽  
J. Ouyang
Keyword(s):  
Coronary Artery ◽  
Skeletal Muscles ◽  
Left Main Coronary Artery ◽  
Fiber Type ◽  
Coronary Artery Ligation ◽  
Ouabain Binding ◽  
Artery Ligation ◽  
Adult Rats ◽  
Type Composition ◽  
Phosphatase Assay

This study was designed to determine whether chronic heart failure (CHF) results in changes in Na+-K+-ATPase properties in heart and skeletal muscles of different fiber-type composition. Adult rats were randomly assigned to a control (Con; n = 8) or CHF ( n = 8) group. CHF was induced by ligation of the left main coronary artery. Examination of Na+-K+-ATPase activity (means ± SE) 12 wk after the ligation measured, using the 3- O-methylfluorescein phosphatase assay (3- O-MFPase), indicated higher ( P < 0.05) levels in soleus (Sol) (250 ± 13 vs. 179 ± 18 nmol·mg protein−1·h−1) and lower ( P < 0.05) levels in diaphragm (Dia) (200 ± 12 vs. 272 ± 27 nmol·mg protein−1·h−1) and left ventricle (LV) (760 ± 62 vs. 992 ± 16 nmol·mg protein−1·h−1) in CHF compared with Con, respectively. Na+-K+-ATPase protein content, measured by the [3H]ouabain binding technique, was higher ( P < 0.05) in white gastrocnemius (WG) (166 ± 12 vs. 135 ± 7.6 pmol/g wet wt) and lower ( P < 0.05) in Sol (193 ± 20 vs. 260 ± 8.6 pmol/g wet wt) and LV (159 ± 10 vs. 221 ± 10 pmol/g wet wt) in CHF compared with Con, respectively. Isoform content in CHF, measured by Western blot techniques, showed both increases (WG; P < 0.05) and decreases (Sol; P < 0.05) in α1. For α2, only increases [red gastrocnemius (RG), Sol, and Dia; P < 0.05] occurred. The β2-isoform was decreased (LV, Sol, RG, and WG; P < 0.05) in CHF, whereas the β1 was both increased (WG and Dia; P < 0.05) and decreased (Sol and LV; P < 0.05). For β3, decreases ( P < 0.05) in RG were observed in CHF, whereas no differences were found in Sol and WG between CHF and Con. It is concluded that CHF results in alterations in Na+-K+-ATPase that are muscle specific and property specific. Although decreases in Na+-K+-ATPase content would appear to explain the lower 3- O-MFPase in the LV, such does not appear to be the case in skeletal muscles where a dissociation between these properties was observed.

Fatigue depresses maximal in vitro skeletal muscle Na+-K+-ATPase activity in untrained and trained individuals

2002 ◽  
Vol 93 (5) ◽  
pp. 1650-1659 ◽  
Author(s):  
Steve F. Fraser ◽  
Jia L. Li ◽  
Michael F. Carey ◽  
Xiao N. Wang ◽  
Termboon Sangkabutra ◽  
...  
Keyword(s):  
Atpase Activity ◽  
Phosphatase Activity ◽  
Important Determinant ◽  
Vastus Lateralis ◽  
Ouabain Binding ◽  
Isokinetic Contractions ◽  
Lower Ratio ◽  
Muscle Biopsies ◽  
Training State

This study investigated whether fatiguing dynamic exercise depresses maximal in vitro Na+-K+-ATPase activity and whether any depression is attenuated with chronic training. Eight untrained (UT), eight resistance-trained (RT), and eight endurance-trained (ET) subjects performed a quadriceps fatigue test, comprising 50 maximal isokinetic contractions (180°/s, 0.5 Hz). Muscle biopsies (vastus lateralis) were taken before and immediately after exercise and were analyzed for maximal in vitro Na+-K+-ATPase (K+-stimulated 3- O-methylfluoroscein phosphatase) activity. Resting samples were analyzed for [3H]ouabain binding site content, which was 16.6 and 18.3% higher ( P < 0.05) in ET than RT and UT, respectively (UT 311 ± 41, RT 302 ± 52, ET 357 ± 29 pmol/g wet wt). 3- O-methylfluoroscein phosphatase activity was depressed at fatigue by −13.8 ± 4.1% ( P < 0.05), with no differences between groups (UT −13 ± 4, RT −9 ± 6, ET −22 ± 6%). During incremental exercise, ET had a lower ratio of rise in plasma K+ concentration to work than UT ( P < 0.05) and tended ( P = 0.09) to be lower than RT (UT 18.5 ± 2.3, RT 16.2 ± 2.2, ET 11.8 ± 0.4 nmol · l−1 · J−1). In conclusion, maximal in vitro Na+-K+-ATPase activity was depressed with fatigue, regardless of training state, suggesting that this may be an important determinant of fatigue.

Ischemia-induced alterations in sarcoplasmic reticulum Ca(2+)-ATPase activity in rat soleus and EDL muscles

1996 ◽  
Vol 271 (6) ◽  
pp. C1942-C1948 ◽  
Author(s):  
H. J. Green ◽  
N. H. McKee ◽  
A. J. Carvalho ◽  
J. C. Dossett-Mercer
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
Time Course ◽  
Extensor Digitorum Longus ◽  
Fiber Type ◽  
Time Dependent ◽  
Fiber Type Composition ◽  
Type Composition ◽  
Edl Muscle ◽  
Muscle Fiber Type Composition

To investigate the time-dependent effects of ischemia, as modified by muscle fiber type composition, on sarcoplasmic reticulum (SR) function, Ca(2+)-ATPase activity (total minus basal) was measured in homogenates prepared from samples obtained from rat soleus and extensor digitorum longus (EDL) muscle of ischemic and contralateral controls. Ischemia was induced by occlusion of blood flow to one hindlimb for periods of 1, 2, and 3 h (n = 10 per group). In EDL, maximal Ca(2+)-ATPase activity (expressed in mumol.g wet wt-1.min-1) was higher (P < 0.05) in ischemic than in control at 1 h (80 +/- 10 vs. 56.5 +/- 5.3) and increased progressively with ischemia at both 2 h (88 +/- 4.6 vs. 53.1 +/- 2.8) and 3 h (116 +/- 3.8 vs. 67.8 +/- 3.2). In contrast, in soleus, increases (P < 0.05) in Ca(2+)-ATPase activity with ischemia were observed at 2 h (19.2 +/- 0.86 vs. 14.0 +/- 0.56) and 3 h (19.9 +/- 1.4 vs. 12.4 +/- 0.62) but not at 1 h (10.7 +/- 1.5 vs. 10.0 +/- 0.83). In both EDL and soleus, basal Mg(2+)-ATPase was unchanged with ischemia. On the basis of these findings, it can be concluded that ischemia results in an increase in the maximal SR Ca(2+)-ATPase activity but that the time course of the change is dependent on the fiber type composition of the muscle.

scholarly journals Development and Validation of a High-Throughput Intrinsic ATPase Activity Assay for the Discovery of MEKK2 Inhibitors

2012 ◽  
Vol 18 (4) ◽  
pp. 388-399 ◽  
Author(s):  
Syed Ahmad ◽  
Mark A. Hughes ◽  
Gary L. Johnson ◽  
John E. Scott
Keyword(s):  
Atpase Activity ◽  
High Throughput ◽  
High Throughput Screening ◽  
Selective Inhibition ◽  
Mass Spectrometry Analysis ◽  
Activity Assay ◽  
Spectrometry Analysis ◽  
Compound Libraries ◽  
Atpase Assay

The kinase MEKK2 (MAP3K2) has recently been implicated in tumor growth and metastasis. Thus, selective inhibition of MEKK2 may be a novel strategy for cancer therapy. To identify inhibitors of MEKK2 kinase activity, we have developed a novel activity assay for MEKK2 based on the discovery that recombinant purified MEKK2 has intrinsic ATPase activity. This MEKK2 ATPase assay was validated for enzyme identity and enzymatic purity by multiple methods including mass spectrometry analysis, testing different sources of MEKK2 and comparing ATPase assay IC50 data for multiple inhibitors to literature values and to IC50 data generated using MEKK2 binding and transphosphorylation assays. Taken together, these data indicated that genuine MEKK2 activity was being measured in this assay and no other ATPases contributed to the signal. A miniaturized version of the assay was validated for high-throughput screening, and compound libraries were screened. The screening hits generated comparable potencies in the MEKK2 intrinsic ATPase, binding, and transphosphorylation assays. We identified a novel MEKK2 inhibitor and confirmed that crizotinib and bosutinib are potent in vitro inhibitors of MEKK2 activity with IC50 values of <100 nM. Thus, this assay has utility for the discovery of small-molecule inhibitors of MEKK2 activity.

Chronic intermittent hypoxia and incremental cycling exercise independently depress muscle in vitro maximal Na+-K+-ATPase activity in well-trained athletes

2005 ◽  
Vol 98 (1) ◽  
pp. 186-192 ◽  
Author(s):  
R. J. Aughey ◽  
C. J. Gore ◽  
A. G. Hahn ◽  
A. P. Garnham ◽  
S. A. Clark ◽  
...  
Keyword(s):  
Atpase Activity ◽  
Vastus Lateralis ◽  
Incremental Exercise ◽  
Peak Oxygen Consumption ◽  
Vastus Lateralis Muscle ◽  
Minor Effect ◽  
Moderate Altitude ◽  
Ouabain Binding ◽  
Before And After

Athletes commonly attempt to enhance performance by training in normoxia but sleeping in hypoxia [live high and train low (LHTL)]. However, chronic hypoxia reduces muscle Na+-K+-ATPase content, whereas fatiguing contractions reduce Na+-K+-ATPase activity, which each may impair performance. We examined whether LHTL and intense exercise would decrease muscle Na+-K+-ATPase activity and whether these effects would be additive and sufficient to impair performance or plasma K+ regulation. Thirteen subjects were randomly assigned to two fitness-matched groups, LHTL ( n = 6) or control (Con, n = 7). LHTL slept at simulated moderate altitude (3,000 m, inspired O2 fraction = 15.48%) for 23 nights and lived and trained by day under normoxic conditions in Canberra (altitude ∼600 m). Con lived, trained, and slept in normoxia. A standardized incremental exercise test was conducted before and after LHTL. A vastus lateralis muscle biopsy was taken at rest and after exercise, before and after LHTL or Con, and analyzed for maximal Na+-K+-ATPase activity [K+-stimulated 3- O-methylfluorescein phosphatase (3- O-MFPase)] and Na+-K+-ATPase content ([3H]ouabain binding sites). 3- O-MFPase activity was decreased by −2.9 ± 2.6% in LHTL ( P < 0.05) and was depressed immediately after exercise ( P < 0.05) similarly in Con and LHTL (−13.0 ± 3.2 and −11.8 ± 1.5%, respectively). Plasma K+ concentration during exercise was unchanged by LHTL; [3H]ouabain binding was unchanged with LHTL or exercise. Peak oxygen consumption was reduced in LHTL ( P < 0.05) but not in Con, whereas exercise work was unchanged in either group. Thus LHTL had a minor effect on, and incremental exercise reduced, Na+-K+-ATPase activity. However, the small LHTL-induced depression of 3- O-MFPase activity was insufficient to adversely affect either K+ regulation or total work performed.

Prolonged exercise to fatigue in humans impairs skeletal muscle Na+-K+-ATPase activity, sarcoplasmic reticulum Ca2+ release, and Ca2+ uptake

2004 ◽  
Vol 97 (4) ◽  
pp. 1414-1423 ◽  
Author(s):  
James A. Leppik ◽  
Robert J. Aughey ◽  
Ivan Medved ◽  
Ian Fairweather ◽  
Michael F. Carey ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
G Protein ◽  
Uptake Rate ◽  
Prolonged Exercise ◽  
Transport Processes ◽  
Vastus Lateralis Muscle ◽  
Ouabain Binding ◽  
Exercise In Humans

Prolonged exhaustive submaximal exercise in humans induces marked metabolic changes, but little is known about effects on muscle Na+-K+-ATPase activity and sarcoplasmic reticulum Ca2+ regulation. We therefore investigated whether these processes were impaired during cycling exercise at 74.3 ± 1.2% maximal O2 uptake (mean ± SE) continued until fatigue in eight healthy subjects (maximal O2 uptake of 3.93 ± 0.69 l/min). A vastus lateralis muscle biopsy was taken at rest, at 10 and 45 min of exercise, and at fatigue. Muscle was analyzed for in vitro Na+-K+-ATPase activity [maximal K+-stimulated 3- O-methylfluorescein phosphatase (3- O-MFPase) activity], Na+-K+-ATPase content ([3H]ouabain binding sites), sarcoplasmic reticulum Ca2+ release rate induced by 4 chloro- m-cresol, and Ca2+ uptake rate. Cycling time to fatigue was 72.18 ± 6.46 min. Muscle 3- O-MFPase activity (nmol·min−1·g protein−1) fell from rest by 6.6 ± 2.1% at 10 min ( P < 0.05), by 10.7 ± 2.3% at 45 min ( P < 0.01), and by 12.6 ± 1.6% at fatigue ( P < 0.01), whereas 3[H]ouabain binding site content was unchanged. Ca2+ release (mmol·min−1·g protein−1) declined from rest by 10.0 ± 3.8% at 45 min ( P < 0.05) and by 17.9 ± 4.1% at fatigue ( P < 0.01), whereas Ca2+ uptake rate fell from rest by 23.8 ± 12.2% at fatigue ( P = 0.05). However, the decline in muscle 3- O-MFPase activity, Ca2+ uptake, and Ca2+ release were variable and not significantly correlated with time to fatigue. Thus prolonged exhaustive exercise impaired each of the maximal in vitro Na+-K+-ATPase activity, Ca2+ release, and Ca2+ uptake rates. This suggests that acutely downregulated muscle Na+, K+, and Ca2+ transport processes may be important factors in fatigue during prolonged exercise in humans.

In Vitro sup 31 Phosphorus-Magnetic Resonance Spectroscopy of Muscle Extracts in Malignant Hyperthermia-susceptible Patients

1996 ◽  
Vol 84 (5) ◽  
pp. 1077-1082 ◽  
Author(s):  
Jean-Francois Payen ◽  
Nathalie Fouilhe ◽  
Ernest Sam-Lai ◽  
Chantal Remy ◽  
Roger Dupeyre ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Malignant Hyperthermia ◽  
Inorganic Phosphate ◽  
Fiber Type ◽  
Resonance Spectroscopy ◽  
Phosphorus Magnetic Resonance Spectroscopy ◽  
Malignant Hyperthermia Susceptible ◽  
Type Composition

Background It was recently suggested that malignant hyperthermia-susceptible (MHS) patients could have an elevated peak of phosphodiesters in leg muscles using in vivo phosphorus magnetic resonance spectroscopy. In the current study, analysis of the phosphodiesters of muscle extracts of MHS and malignant hyperthermia-negative patients was performed using in vitro phosphorus magnetic resonance spectroscopy to chemically identify and to compare the muscle concentrations of water-soluble compounds between the two groups with respect to the muscle fiber type composition. Methods Perchloric acid extracts of the vastus medialis muscle of seven MHS patients and ten malignant hyperthermia-negative patients on the basis of the European malignant hyperthermia contracture test were subjected to in vitro phosphorus magnetic resonance spectroscopy carried out at 9.4 T. In addition, chemical identification of the phosphodiester region and histologic examination of the muscle specimens were performed. Results The peak in the phosphodiester region was assigned to glycerophosphorylcholine. Muscle perchloric acid extracts of MHS patients had a significantly (P &lt; 0.05) higher glycerophosphorylcholine to the sum of phosphocreatine and inorganic phosphate (glycerophosphorylcholine/ [phosphocreatine +inorganic phosphate]) value than those of malignant hyperthermia-negative patients. Neither a difference in the fiber type composition between the two groups nor any specific myopathy were found. Conclusions In the absence of histologic differences between muscle specimens of MHS and malignant hyperthermia-negative patients, these results could suggest that glycerophosphorylcholine could be a marker of an impairment in the phospholipid metabolism in the skeletal muscle of MHS patients.

Effect of Aldosterone on the Human Erythrocyte Sodium-Potassium Pump in vitro

1983 ◽  
Vol 64 (2) ◽  
pp. 183-186 ◽  
Author(s):  
N. Stern ◽  
F. Beck ◽  
J. Sowers
Keyword(s):  
Atpase Activity ◽  
Human Erythrocyte ◽  
Erythrocyte Membranes ◽  
Ouabain Binding ◽  
Physiological Concentration ◽  
Sodium Potassium ◽  
Human Erythrocyte Membranes ◽  
Erythrocyte Sodium ◽  
Sodium Potassium Pump

1. The effects of aldosterone in vitro on the Na+,K+-dependent ATPase activity of isolated human erythrocyte membranes and on rubidium (86Rb) uptake and [3H]ouabain binding of intact erythrocytes were studied. 2. ATPase activity was nearly doubled (0.061 ± 0.006 to 0.110 ± 0.01 μmol of Pl h−1 mg−1 of protein) by the addition of a physiological concentration of aldosterone (2.7 × 10-10 mol/l). Higher concentrations had no greater effect. 3. Aldosterone had no significant effect on 86Rb uptake or [3H]ouabain binding. 4. Erythrocytes contain aldosterone at concentrations similar to that in plasma. The effect of aldosterone on ATPase is probably maximal.

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