Mg2+-HCO-3-ATPase and carbonic anhydrase in rat intestinal mucosa

Mg2+-dependent and HCO-3-stimulated ATPase activity was highest in the brush border (microvilli) of rat duodenal mucosa compared with that of the other gastrointestinal mucosa. This ATPase may be useful to neutralize the gastric acid in the duodenal lumen. Carbonic anhydrase seems to accomplish a subsidiary role in the above reaction.     

Iron-mediated inhibition of H+-ATPase in plasma membrane vesicles isolated from wheat roots

The mechanisms of iron-mediated inhibition of the H(+)-ATPase activity of plasma membrane (PM) vesicles isolated from wheat roots were investigated. Both FeSO(4) and FeCl(3) significantly inhibited PM H(+)-ATPase activity, and the inhibition could be reversed by the addition of the metal ion chelator EDTA-Na(2) or a specific Fe(2+) chelator, indicating that the inhibitory effect was due to specific action of Fe(2+) or Fe(3+). Measurement of the extent of lipid peroxidation showed that oxidative damage on the PM caused by Fe(2+) or Fe(3+) seemed to be correlated with the inhibition of PM H(+)-ATPase activity. However, prevention of lipid peroxidation with butylated hydroxytoluene did not affect iron-mediated inhibition in the PM H(+)-ATPase, suggesting that the inhibition of the PM H(+)-ATPase was not a consequence of lipid peroxidation caused by iron. Investigation of the effects of various reactive oxygen species scavengers on the iron-mediated inhibition of H(+)-ATPase activity indicated that hydroxyl radicals (*OH) and hydrogen peroxide (H(2)O(2)) might be involved in the Fe(2+)-mediated decrease in PM H(+)-ATPase activity. Moreover, iron caused a decrease in plasma protein thiol (P-SH), and Fe(3+) brought a higher degree of oxidation in thiol groups than Fe(2+) at the same concentration. Modification of the thiol redox state in the PM suggested that reducing thiol groups were essential to maintain PM H(+)-ATPase activity. Incubation of the specific thiol modification reagent 5,5-dithio-bis(2-nitrobenzoic acid) with the rightside-out and inside-out PM revealed that thiol oxidation occurred at the apoplast side of the PM. Western blotting analysis revealed a decrease in H(+)-ATPase content caused by iron. Taken together, these results suggested that thiol oxidation might account for the inhibition of PM H(+)-ATPase caused by iron, and that *OH and H(2)O(2) were also involved in Fe(2+)-mediated inhibition.     

Effects of various inhibitors and 2,4-dinitrophenol on adenosine triphosphatase from Malpighian tubules ofLocusta migratoria L

Summary Both Mg²⁺-ATPase and HCO ₃ ^– -stimulated ATPase activity were inhibited by sodium azide and to a lesser extent ethacrynic acid and amiloride. 1 mM DNP stimulated Mg²⁺-ATPase activity by 22% and HCO ₃ ^– -stimulated ATPase activity by 7%.     

Possible role of intestinal alkaline phosphatase activity in thiamine transport.

Thiamine deficiency caused a marked decrease of intestinal alkaline phosphatase (al-Pase) activity, but had no effect on the Ca++-ATPase activity and Ca++-absorption in rats. The al-Pase activity was significantly decreased 1 h after oral administration of ethanol at 0.5 and 2.5 g/kg. In contrast, Mg++-, Ca++-and (Na+ + K+)-ATPase activities did not change after the administration of ethanol. These findings show that the al-Pase activity, unlike the Ca++-ATPase activity, is not related to Ca++-absorption. A possible role of al-Pase activity in the active transport of thiamine in the intestine was discussed.     

HCO 3 − -ATPase activity distribution in rat liver cell fractions prepared by zonal centrifugation

Summary Plasma membrane sheets prepared by zonal centrifugation of a premicrosomal pellet obtained from a rat liver homogenate are devoid of HCO ₃ ^– -ATPase activity. Since the microsomal fraction is also lacking in this ATPase activity, it can be concluded that the HCO ₃ ^– -ATPase is not involved in the secretion of HCO ₃ ^– into bile. Acknowledgments. This investigation was supported in part by grants No. DE-02600 and AM 80686 from the United States Public Health Service. The A-XII zonal rotor is used under subcontract No. 3796 with the Union Carbide Corporation.     

Lack of Na+,K+-ATPase expression in intercalated cells may be compensated by Na+-ATPase: A study on MDCK – C11 cells

The lack of Na⁺,K⁺-ATPase expression in intercalated cells (IC) is an intriguing condition due to its fundamental role in cellular homeostasis. In order to better understand this question we compared the activities of Na⁺,K⁺-ATPase and Na⁺-ATPase in two MDCK cell clones: the C11, with IC characteristics, and the C7, with principal cells (PC) characteristics. The Na⁺,K⁺-ATPase activity found in C11 cells is far lower than in C7 cells and the expression of its β-subunit is similar in both cells. On the other hand, a subset of C11 without α-subunit expression has been found. In C11 cells the Na⁺-ATPase activity is higher than that of the Na⁺,K⁺-ATPase, and it is increased by medium alkalinization, suggesting that it could account for the cellular Na⁺-homeostasis. Although further studies are necessary for a better understanding of these findings, the presence of Na⁺-ATPase may explain the adequate survival of cells that lack Na⁺,K⁺-ATPase. Received 09 July 2008; received after revision 03 August 2008; accepted 12 August 2008     

Influence of ethanol on calcium, inositol phospholipids and intracellular signalling mechanisms

Studies have implicated Ca++ in the actions of ethanol at many biochemical levels. Calcium as a major intracellular messenger in the central nervous system is involved in many processes, including protein phosphorylation enzyme activation and secretion of hormones and neurotransmitters. The control of intracellular calcium, therefore, represents a major step by which neuronal cells regulate their activities. The present review focuses on three primary areas which influence intracellular calcium levels; voltage-dependent Ca++ channels, receptor-mediated inositol phospholipid hydrolysis, and Ca++/Mg++-ATPase, the high affinity membrane Ca++ pump. Current research suggests that a subtype of the voltage-dependent Ca++ channel, the dihydropyridine-sensitive Ca++ channel, is uniquely sensitive to acute and chronic ethanol treatment. Acute exposure inhibits, while chronic ethanol exposure increases 45Ca++-influx and [3H]dihydropyridine receptor binding sites. In addition, acute and chronic exposure to ethanol inhibits, then increases Ca++/Mg++-ATPase activity in neuronal membranes. Changes in Ca++ channel and Ca++/Mg++-ATPase activity following chronic ethanol may occur as an adaptation process to increase Ca++ availability for intracellular processes. Since receptor-dependent inositol phospholipid hydrolysis is enhanced after chronic ethanol treatment, subsequent activation of protein kinase-C may also be involved in the adaptation process and may indicate increased coupling for receptor-dependent changes in Ca++/Mg++-ATPase activity. The increased sensitivity of three Ca++-dependent processes suggest that adaptation to chronic ethanol exposure may involve coupling of one or more of these processes to receptor-mediated events.     

A histochemical demonstration of the Na+ + K+-ATPase activity in the thyroid and the effect of cyclic adenosine monophosphate (c-AMP).

With a suitable modification of the Farquhar and Palade technique the Na+ + K+-ATPase activity in guinea-pig thyroid is demonstrated. The addition of c-AMP (5 X 10(-6) M or 1.5 X 10(-5) M) to the incubation media produced an apparent intensification of the Na+ + K+ -ATPase activity in the thyroid.     

Possible role of intestinal alkaline phosphatase activity in thiamine transport

Summary Thiamine deficiency caused a marked decrease of intestinal alkaline phosphatase (al-Pase) activity, but had no effect on the Ca⁺⁺-ATPase activity and Ca⁺⁺-absorption in rats. The al-Pase activity was significantly decreased 1 h after oral administration of ethanol at 0.5 and 2.5 g/kg. In contrast, Mg⁺⁺-, Ca⁺⁺- and (Na⁺+K⁺)-ATPase activities did not change after the administration of ethanol. These findings show that the al-Pase activity, unlike the Ca⁺⁺-ATPase activity, is not related to Ca⁺⁺-absorption. A possible role of al-Pase activity in the active transport of thiamine in the intestine was discussed.     

Inhibition of hepatic Na +, K + -adenosinetriphosphatase in taurolithocholate-induced cholestasis in the rat.

Na +, K + -adenosinetriphosphatase (Na +, K + -ATPase) activity was decreased in liver plasma membranes from rats in which cholestasis had been induced by i.v. administration of sodium taurolithocholate (5 mumoles/100 g b. wt). Incubation of liver plasma membranes with taurolithocholate (10--1300 muM) caused significant and dose dependent reductions of Na +, K + -ATPase activity at taurolithocholate concentrations above 100 muM. These findings lend support to the hypothesis that cholestasis induced by monohydroxy bile acids is at least partially the result of an inhibition of hepatic Na +, K + -ATPase activity.     

The effect of physostigmine on (Na+ + K+)-ATPase activity in different rat brain regions

The activity of (Na+ + K+)-ATPase and acetylcholine esterase were followed in rat brain cerebral cortex, caudate, thalamus, hippocampus and medulla after i.v. administration of physostigmine. Both enzymes were found to be inhibited in a dose-dependent manner. The most pronounced inhibition of (Na+ + K+)-ATPase was found in caudate, where the highest activity of acetylcholine esterase is found.     

Further evidence for the dissociation of digoxin-like immunoreactivity from Na+,K(+)-ATPase inhibitory activity

The effects of adrenalectomy or nephrectomy, carried out one hour previously, on the levels of endogenous digitalis-like factors were determined in rat plasma. Factors were assayed by digoxin-like immunoreactivity and direct Na+,K(+)-ATPase inhibitory activity. Digoxin-like immunoreactivity significantly decreased one hour after bilateral ablation of adrenals, while Na+,K(+)-ATPase inhibitory activity remained unaltered. There were no changes in either activity one hour after bilateral nephrectomy. These results suggest that digoxin-like immunoreactivity may be derived from the adrenal gland or under adrenal control and the major substances detected by digoxin-like immunoreactivity and direct Na+,K(+)-ATPase inhibitory activity may be different.     

The (Na+ + K+)-ATPase activity in brain of Quaking mice.

The (Na+ 4 K+)- and Mg2+-dependent ATPase distribution in several brain areas has been investigated in Quaking mutant mice characterized by myelin deficiency. A marked decrease of (Na+ + K+)-ATPase activity has been found in limbic structures, hypothalamus and cerebellum. The Mg2+-dependent activity did not change. A possible involvement of the impairment of the (Na+ + K+)-ATPase activity in the seizure susceptibility of this mice is discussed.     

Further evidence for the dissociation of digoxin-like immunoreactivity from Na+, K+-ATPase inhibitory activity

Summary The effects of adrenalectomy or nephrectomy, carried out one hour previously, on the levels of endogenous digitalis-like factors were determined in rat plasma. Factors were assayed by digoxin-like immunoreactivity and direct Na⁺, K⁺-ATPase inhibitory activity. Digoxin-like immunoreactivity significantly decreased one hour after bilateral ablation of adrenals, while Na⁺, K⁺-ATPase inhibitory activity remained unaltered. There were no changes in either activity one hour after bilateral nephrectomy. These results suggest that digoxin-like immunoreactivity may be derived from the adrenal gland or under adrenal control and the major substances detected by digoxin-like immunoreactivity and direct Na⁺, K⁺-ATPase inhibitory activity may be different.     

Influence of ethanol on calcium,inositol phospholipids and intracellular signalling mechanisms

Summary Studies have implicated Ca⁺⁺ in the actions of ethanol at many biochemical levels. Calcium as a major intracellular messenger in the central nervous system is involved in many processes, including protein phosphorylation enzyme activation and secretion of hormones and neurotransmitters. The control of intracellular calcium, therefore, represents a major step by which neuronal cells regulate their activities. The present review focuses on three primary areas which influence intracellular calcium levels; voltage-dependent Ca⁺⁺ channels, receptor-mediated inositol phospholipid hydrolysis, and Ca⁺⁺/Mg⁺⁺-ATPase, the high affinity membrane Ca⁺⁺ pump.Current research suggests that a subtype of the voltage-dependent Ca⁺⁺ channel, the dihydropyridine-sensitive Ca⁺⁺ channel, is uniquely sensitive to acute and chronic ethanol treatment. Acute exposure inhibits, while chronic ethanol exposure increases⁴⁵Ca⁺⁺-influx and [³H]dihydropyridine receptor binding sites. In addition, acute and chronic exposure to ethanol inhibits, then increases Ca⁺⁺/Mg⁺⁺-ATPase activity in neuronal membranes. Changes in Ca⁺⁺ channel and Ca⁺⁺/Mg⁺⁺-ATPase activity following chronic ethanol may occur as an adaptation process to increase Ca⁺⁺ availability for intracellular processes. Since receptor-dependent inositol phospholipid hydrolysis is enhanced after chronic ethanol treatment, subsequent activation of protein kinase-C may also be involved in the adaptation process and may indicate increased coupling for receptor-dependent changes in Ca⁺⁺/Mg⁺⁺-ATPase activity.The increased sensitivity of three Ca⁺⁺-dependent processes suggest that adaptation to chronic ethanol exposure may involve coupling of one or more of these processes to receptor-mediated events.     

Changes in rat ventricular myosin in old age

Myosin was isolated from rat ventricular myocardium, and its properties were compared in adult and very old animals. Ca2+ -ATPase activity of ventricular myosin was found to be lower in very old animals as compared with adult ones; K+ -ATPase activity, however, does not change with the aging process. Neither were there any differences between the two age groups in the pattern of ventricular light chains of myosin.     

The effect of physostigmine on (Na++K+)-ATPase activity in different rat brain regions

Summary The activity of (Na⁺+K⁺)-ATPase and acetylcholine esterase were folloed in rat brain cerebral cortex, caudate, thalamus, hippocampus and medulla after i.v. administration of physostigmine. Both enzymes were found to be inhibited in a dose-dependent manner. The most pronounced inhibition of (Na⁺+K⁺)-ATPase was found in caudate. where the highest activity of acetylcholine esterase is found.These studies were supported by a grant from the Union of Science of Republic Serbia, No. 40404-14.     

A histochemical demonstration of the Na++K+-ATPase activity in the thyroid and the effect of cyclic adenosine monophosphate (c-AMP)

Summary With a suitable modification of the Farquhar and Palade technique the Na⁺+K⁺-ATPase activity in guineapig thyroid is demonstrated. The addition of c-AMP (5×10^–6 M or 1.5×10^–5 M) to the incubation media produced an apparent intensification of the Na⁺+K⁺-ATPase activity in the thyroid.This work was supported by a grant from ZMNU of Serbia.     

Insulin effect in vitro on human erythrocyte plasma membrane

The effect of porcine insulin has been tested in vitro on human erythrocyte plasma membrane (Na+-K+) and Mg2+-ATPase activities as well as on membrane fluidity. The results indicate that the hormonal treatment significantly inhibits (Na+-K+)-ATPase activity, and at the same time decreases membrane fluidity.     

Effect of clofibrate on the enzyme activity of rat liver plasma membranes

Summary The activity of 3 plasma membranes marker enzymes (5-nucleotidase, Mg⁺⁺-ATPase and alkaline phosphodiesterase-I) was determined in plasma membranes isolated from liver of control and of clofibrate-treated rats. A complete identity of plasma membranes enzyme activity in the 2 groups of experimental animals was observed for the 3 enzymes studied.