High glucose levels induce inhibition of Na,K-ATPase via stimulation of aldose reductase, formation of microtubules and formation of an acetylated tubulin/Na,K-ATPase complex (original) (raw)
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Tubulin–Na + , K + ‐ATPase interaction: Involvement in enzymatic regulation and cellular function
Journal of Cellular Physiology, 2018
A new function for tubulin was described by our laboratory: acetylated tubulin forms a complex with Na + ,K +-ATPase (NKA) and inhibits its activity. This process was shown to be a regulatory factor of physiological importance in cultured cells, human erythrocytes, and several rat tissues. Formation of the acetylated tubulin-NKA complex is reversible. We demonstrated that in cultured cells, high concentrations of glucose induce translocation of acetylated tubulin from cytoplasm to plasma membrane with a consequent inhibition of NKA activity. This effect is reversed by adding glutamate, which is coctransported to the cell with Na +. Another posttranslational modification of tubulin, detyrosinated tubulin, is also involved in the regulation of NKA activity: it enhances the NKA inhibition induced by acetylated tubulin. Manipulation of the content of these modifications of tubulin could work as a new strategy to maintain homeostasis of Na + and K + , and to regulate a variety of functions in which NKA is involved, such as osmotic fragility and deformability of human erythrocytes. The results summarized in this review show that the interaction between tubulin and NKA plays an important role in cellular physiology, both in the regulation of Na + /K + homeostasis and in the rheological properties of the cells, which is mechanically different from other roles reported up to now.
Tubulin–Na + , K + ‐ATPase interaction: Involvement in enzymatic regulation and cellular function
Journal of Cellular Physiology, 2018
A new function for tubulin was described by our laboratory: acetylated tubulin forms a complex with Na + ,K +-ATPase (NKA) and inhibits its activity. This process was shown to be a regulatory factor of physiological importance in cultured cells, human erythrocytes, and several rat tissues. Formation of the acetylated tubulin-NKA complex is reversible. We demonstrated that in cultured cells, high concentrations of glucose induce translocation of acetylated tubulin from cytoplasm to plasma membrane with a consequent inhibition of NKA activity. This effect is reversed by adding glutamate, which is coctransported to the cell with Na +. Another posttranslational modification of tubulin, detyrosinated tubulin, is also involved in the regulation of NKA activity: it enhances the NKA inhibition induced by acetylated tubulin. Manipulation of the content of these modifications of tubulin could work as a new strategy to maintain homeostasis of Na + and K + , and to regulate a variety of functions in which NKA is involved, such as osmotic fragility and deformability of human erythrocytes. The results summarized in this review show that the interaction between tubulin and NKA plays an important role in cellular physiology, both in the regulation of Na + /K + homeostasis and in the rheological properties of the cells, which is mechanically different from other roles reported up to now.
Molecular and Cellular Biochemistry, 2006
In cells of neural and non-neural origin, tubulin forms a complex with plasma membrane Na + ,K +-ATPase, resulting in inhibition of the enzyme activity. When cells are treated with 1 mM L-glutamate, the complex is dissociated and enzyme activity is restored. Now, we found that in CAD cells, ATPase is not activated by L-glutamate and tubulin/ATPase complex is not present in membranes. By investigating the causes for this characteristic, we found that tubulin must be acetylated in order to associate with ATPase and to inhibit its catalytic activity. In CAD cells, the acetylated tubulin isotype is absent. Treatment of CAD cells with deacetylase inhibitors (trichostatin A or tubacin) caused appearance of acetylated tubulin, formation of tubulin/ATPase complex, and reduction of membrane ATPase activity. In these treated cells, addition of 1 mM L-glutamate dissociated the complex and restored the enzyme activity. Cytosolic tubulin from trichostatin A-treated but not from non-treated cells inhibited ATPase activity. These findings indicate that the acetylated isotype of tubulin is required for interaction with membrane Na + ,K +-ATPase and consequent inhibition of enzyme activity.
Intracellular sodium in proximal tubules of diabetic rats. Role of glucose
Kidney International, 1988
Intracellular sodium in proximal tubules of diabetic rats. Role of glucose. Renal hypertrophy is a common consequence of diabetes mellitus that precedes and possibly accounts for the increased glomerular filtration rate. We have postulated that the glucose-mediated increase in the intracellular concentration of sodium [Na]1 initiates the chain of events leading to the increase in cell size and eventually cell number. Experiments were conducted on Sprague-Dawley rats made diabetic by the intravenous injection of 45 mg/kg body wt of streptozotocin dissolved in a 5 m citrate buffer solution. Control animals were injected with the vehicle alone. Ninety-six hours and 11 weeks later, measurements of [Na]1 were done by NMR spectroscopy on suspensions of proximal tubules, using dysprosium tripolyphosphate as an extracellular shift reagent. At 96 hours after the induction of the diabetes, there was a 60% increase in [Na]1 compared to control (P < 0.01). No further increase in [Na]1 was observed during the subsequent II weeks of observation. Addition of ouabain (1.0 mM) resulted in a fourfold increase in [Na]1 in tubules from control animals, and a 2.5-fold increase in tubules from 96-hour diabetic rats. Ouabain-inhibitable Na-K-ATPase activity was substantially higher in the renal tubules of diabetic rats, the increase being proportional to that of [Na]1. In order to ascertain the effect of hyperglycemia on [Na]1, proximal tubules prepared from kidneys of normal and diabetic rats were exposed to low (5 mM) and high (25 mM) concentration of glucose in the media. The rise in glucose concentration resulted in a 52% increase (P < 0.001) in [Na]1 in proximal tubules of non-diabetic animals, whereas the increase was only 11% (P > 0.2) in the 96-hour diabetics, and 5% (P > 0.2) in Il-week diabetic rats. Based on these findings, it is reasonable to propose that the rise in [Na]1 observed in the proximal tubules of diabetic rats is due to increased filtered load of glucose that stimulates the entry of glucose and Na into renal cells. The relationship between the rise in [Na]1 and cell growth remains speculative, although an association between these events has been documented consistently in the literature.
Febs Journal, 2005
In the yeast Saccharomyces cerevisiae, plasma membrane H+-ATPase is activated by d-glucose. We found that in the absence of glucose, this enzyme forms a complex with acetylated tubulin. Acetylated tubulin usually displays hydrophilic properties, but behaves as a hydrophobic compound when complexed with H+-ATPase, and therefore partitions into a detergent phase. When cells were treated with glucose, the H+-ATPase–tubulin complex was disrupted, with two consequences, namely (a) the level of acetylated tubulin in the plasma membrane decreased as a function of glucose concentration and (b) the H+-ATPase activity increased as a function of glucose concentration, as measured by both ATP-hydrolyzing capacity and H+-pumping activity. The addition of 2-deoxy-d-glucose inhibited the above glucose-induced phenomena, suggesting the involvement of glucose transporters. Whereas total tubulin is distributed uniformly throughout the cell, acetylated tubulin is concentrated near the plasma membrane. Results from immunoprecipitation experiments using anti-(acetylated tubulin) and anti-(H+-ATPase) immunoglobulins indicated a physical interaction between H+-ATPase and acetylated tubulin in the membranes of glucose-starved cells. When cells were pretreated with 1 mm glucose, this interaction was disrupted. Double immunofluorescence, observed by confocal microscopy, indicated that H+-ATPase and acetylated tubulin partially colocalize at the periphery of glucose-starved cells, with predominance at the outer and inner sides of the membrane, respectively. Colocalization was not observed when cells were pretreated with 1 mm glucose, reinforcing the idea that glucose treatment produces dissociation of the H+-ATPase–tubulin complex. Biochemical experiments using isolated membranes from yeast and purified tubulin from rat brain demonstrated inhibition of H+-ATPase activity by acetylated tubulin and concomitant increase of the H+-ATP ase–tubulin complex.
MOLECULAR CHANGES IN PROXIMAL TUBULE FUNCTION IN DIABETES MELLITUS
Clinical and Experimental Pharmacology and Physiology, 2004
1. Diabetic kidney disease is initially associated with hypertension and increased urinary albumin excretion. The hypertension is mediated by enhanced volume expansion due to enhanced salt and water retention by the kidney. The increased urinary albumin is not only due to increased glomerular leak, but also to a decrease in albumin reabsorption by the proximal tubule. The precise molecular mechanisms underlying these two phenomena and whether there is any link between the increase in Na + retention and proteinuria remain unresolved.
Na/K-ATPase Activity and Ketone Body Metabolism in Long-term Diabetic Rats
2019
The long-term (34 weeks) effect of streptozotocin induced diabetes was assessed in Wistar rats.Na+/K+-ATPase activity was measured by ouabain inhibitable86Rb+-uptake into erythrocytes. No difference in the rate of Rb+-uptake, the Kmfor Rb+or the Kifor ouabain was detected between normal and diabetic rats. Thus, the change in Na+/K+-ATPase activity repeatedly described in short-term studies may not translate into a long term physiologically relevant change in ion flux through the sodium pump.Rats excrete ketone bodies mainly as β-hydroxybutyrate. This compound does not show up with nitroprusside sodium based test sticks, it can however be detected by coupled spectrophotometric assay with hydroxybutyrate dehydrogenase.Almost half of the diabetic animals reverted to a non-diabetic state during the experiment, followed by at least partial reversal of secondary diabetic damage.Abbreviations usedPKCProtein kinase CDAGDiacylglycerolEDTAEthylenediamine tetraacetic acidPIP3Phosphatidylinosit...
In vitro insulin action on different ATPases of erythrocyte membranes in normal and diabetic rats
Acta Diabetologica, 1985
Thein vitro effect of porcine insulin on Na++K+-, Ca2+- and Mg2+-ATPases of the rat erythrocyte membrane of normal and alloxan-induced diabetic rats was investigated. Na++K+- and Ca2+-stimulated enzyme activities were significantly decreased in diabetic rats in comparison to normal animals. The specific activities of both these ATPases in the latter group were markedly reduced on pre-incubating the ghosts with insulin. Similar treatment of the erythrocyte membranes of diabetic animals, however, resulted in a significant increase of these activities. These qualitatively different effects of the hormone in the two groups increased progressively with hormone concentration and duration of pre-incubation. Mg2+-stimulated ATPase activity was not significantly affected in diabetes or by insulin.