Effect of mycotoxin (T-2 toxin) on catecholamine and Na+, K+-ATPase levels in rat epididymis

Summary The effect of mycotoxin (T-2 toxin) on catecholamines and Na⁺, K⁺-ATPase activities in rat epididymis has been evaluated. Dopamine and norepinephrine levels were significantly elevated in the caput and corpus regions whereas their levels remained unchanged in the caudal part of the epididymis. Na⁺, K⁺-ATPase activity was significantly increased in all the three regions of rat epididymis as a result of the toxin treatment. These changes may suggest an adverse effect on epididymal functions in rats.     

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.     

Dissociation of digoxin-like immunoreactivity and Na+,K+-ATPase inhibitory activity in rat plasma

We measured endogenous digitalis-like factor (EDF) in rat plasma during acute saline infusion by two different procedures. Na+,K+-ATPase inhibitory activity in the rat plasma significantly increased during saline loading (7.8 +/- 2.2 vs 2.5 +/- 0.9%, with and without acute saline loading, respectively, p less than 0.05). On the other hand, the plasma digoxin-like immunoreactivity significantly decreased during acute saline loading (16.9 +/- 1.6 vs 32.0 +/- 2.8 pg digoxin equivalents/ml, with and without acute saline loading, respectively, p less than 0.01). These results indicate that the major substances detected by digoxin-like immunoreactivity and direct Na+,K+-ATPase inhibitory activity are completely different, at least in rat plasma.     

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.     

Purification from human plasma of endogenous sodium transport inhibitor(s)

Na+,K+-ATPase inhibitors extracted from plasma of healthy human subjects displaced 3H-ouabain binding to human erythrocytes and inhibited the Na+ efflux catalyzed by the Na+,K+-pump and unexpectedly the Na+,K+-cotransport system without alteration of the Na+,Na+-exchange or the Na+ passive permeability. This suggests the presence in healthy human plasma of endogenous factors with ouabain-like and furosemide-like activities.     

Increase in Na+, K+ -ATPase enzyme units in liver and kidneys from essential fatty acid deficient rats.

(3H)-Ouabain binding to liver and kidney preparations was utilized to estimate the number of Na+, K+-ATPase enzyme units in livers and kidneys from rats fed 2% corn oil supplemented or fat-free diets. The specific (3H)-ouabain binding in liver and kidney preparations from fatty acid deficient rats was increased approximately 40%, but the affinity of the binding sites for ouabain (Kd-value) remained unchanged. The increased concentration of Na+, K+-ATPase enzyme units observed in the essential fatty acid deficient rats may contribute to the reduced body fat accumulation and elevated heat production observed in these animals.     

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.     

Inhibition of microsomal Na+ K+ ATPase of the brain by extracts of Mansonia altissima]

Water extracts of the bark of Mansonia altissima var altissima inhibit the activity of the Na+, K+-ATPase of Rabbit brain microsomes. The kinetics of hydrolysis of ATP show non-competitive inhibition analogous to that produced by ouabain.     

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.     

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.     

Effect of free fatty acids and cholesterol in vitro on liver plasma membrane-bound enzymes

The effect of cholesterol and fatty acid treatment in vitro was tested on rat liver plasma membrane-bound enzymes and lipid fluidity. The observed alterations of membrane fluidity affect both (Na+-K+)-ATPase and Mg2+-ATPase activities but not 5'-nucleotidase; basal adenylate cyclase as well as its hormonal sensitivity were differentially affected by changes of membrane microenvironment.     

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.     

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.     

Characterization of the (Na+-K+)-ATPase from endometrial plasma membranes of immature mammals]

The (Na+-K+)-ATPase in plasma membrane from Mammiferous endometrium is characterized by the Mg/ATP ratio equal to one, and by a distinct affinity for Na+ (1.3 mM) and K+ (2 mM). The activity is maximum for pH 7.4-7.5 in presence of Mg++ 2mM and ATP 2 mM, Na+ 140 mM and K+ 10 mM.     

Inhibitory effect of ouabain on in vitro and in vivo gastric acid secretion in the frog and the rat

The in vitro and in vivo effects of ouabain on gastric acid secretion in the frog and the rat, the 2 species known to have different sensitivity to ouabain, were studied. It was found that ouabain was a potent inhibitor of histamine-stimulated acid secretion in the isolated frog gastric mucosa. Ouabain administered i.v. at dose levels far below the lethal range also produced a marked and significant reduction of histamine-stimulated gastric acid secretion in the anesthetized frogs and rats. It is considered that the inhibitory effect of ouabain on acid secretion could be partly related to its specific antagonizing action on the Na+ -K+ -ATPase in the gastric mucosa.     

Alteration of erythrocyte (see article) -ATPase by replacement of cholesterol by desmosterol in the membrane.

Cholesterol of red blood cells (RBC) is readily exchanged by desmosterol and vice versa. The resulting alteration in the sterol composition influences the specific (Na+ plus K+)-ATPase activity. It is suggested that this effect is due to an altered membrane fluidity.     

Reversal by lecithin of the amobarbital-induced inhibition of microsomal (Na+K)-activated ATPase

Résumé L'amobarbital de soude inhibe l'activité du (Na+K)-ATPase du réticule sarcoplasmique isolé. Cette inhibition peut être évitée par l'addition de lécithine purifiée. La lécithine pré-incubée en présence de l'amobarbital inhibe (Na+K)-ATPase.     

Decreased monosaccharide transport in renal brush-border membrane vesicles of spontaneously hypertensive rats

Na(+)-dependent D-glucose and D-galactose transport were studied in brush-border membrane vesicles (BBMVs) from kidney cortex isolated from both spontaneously hypertensive rats (SHR) and their normotensive genetic control Wistar-Kyoto (WKY) rats. Initial rates and accumulation ratios of Na(+)-dependent D-glucose and D-galactose transport were significantly lower in SHR compared with WKY, the observed decreases being similar for both substrates. To explain the reduction in sugar transport by renal BBMVs, the density of Na(+)-dependent sugar cotransporters was studied in BBMVs from kidney cortex isolated from SHR and WKY rats. Phlorizin-specific binding and Western blot analysis indicated a reduction in the density of the cotransporters in SHR relative to WKY rats. This reduction was similar to those found for the initial rates and accumulation ratios for D-glucose and D-galactose in SHR. Na+ uptake, studied using 22Na+, was significantly increased in SHR, so the observed reduction in sugar transport could be due to disruption of the Na+ gradient between renal BBMVs in SHR. Furthermore, a significant decrease in the activity of Na(+)-K(+)-ATPase was observed in SHR. In conclusion, changes in the density of the Na(+)-dependent sugar cotransporter and in the Na+ gradient across the brush-border membranes might be involved in the observed reduction in sugar transport by renal BBMVs from SHR.     

Cytochemical localization of the K+ regulation interface between blood and brain.

Phosphatase activity identified with Na+-K+-ATPase was localized at the basal surface of cerebral cortical capillary endothelium by perfusion with a p-nitrophenyl phosphate-strontium medium. The relationship of this to the blood-brain barrier to K+ is discussed.     

Unordered structured of proinsulin C-peptide in aqueous solution and in the presence of lipid vesicles

Proinsulin C-peptide ameliorates renal and autonomic nerve function and increases skeletal muscle blood flow, oxygen uptake and glucose transport in patients with insulin-dependent diabetes mellitus. These effects have in part been ascribed to the stimulatory influence of C-peptide on Na+,K+-ATPase and endothelial nitric oxide synthase. To evaluate the capacity of C-peptide to insert into lipid bilayers and form ion channels, C-peptide secondary structure and membrane interactions were studied with circular dichroism spectroscopy and size exclusion chromatography. C-peptide is shown to lack a stable secondary structure, both when part of proinsulin and when free in aqueous solution, although the N-terminal third of the peptide exhibits an alpha-helical conformation in trifluoroethanol. Moreover, C-peptide remains disordered in the aqueous solvent in the presence of lipid vesicles, regardless of vesicle composition. In conclusion, C-peptide is unlikely to elicit physiological effects through stable conformation-dependent interactions with lipid membranes.