Epigallocatechin-3-gallate is an inhibitor of Na,K-ATPase by favoring the E1 conformation

Four catechins, epigallocatechin-3-gallate, epigallocatechin, epicatechin-3-gallate, and epicatechin, inhibited activity of the Na⁺,K⁺-ATPase. The two galloyl-type catechins were more potent inhibitors, with IC₅₀ values of about 1 μM, than were the other two catechins. Inhibition by epigallocatechin-3-gallate was noncompetitive with respect to ATP. Epigallocatechin-3-gallate reduced the affinity of vanadate, shifted the equilibrium of E₁P and E₂P toward E₁P, and reduced the rate of the E₁P to E₂P transition. Epigallocatechin-3-gallate potently inhibited membrane-embedded P-type ATPases (gastric H⁺,K⁺-ATPase and sarcoplasmic reticulum Ca²⁺-ATPase) as well as the Na⁺,K⁺-ATPase, whereas soluble ATPases (bacterial F₁-ATPase and myosin ATPase) were weakly inhibited. Solubilization of the Na⁺,K⁺-ATPase with a nonionic detergent reduced sensitivity to epigallocatechin-3-gallate with an elevation of IC₅₀ to 10 μM. These results suggest that epigallocatechin-3-gallate exerts its inhibitory effect through interaction with plasma membrane phospholipid.     

Modulators of ion-transporting ATPases

This review focuses on ion-transporting ATPases which play an essential role in the generation and maintenance of ionic gradients between cell compartments and environment. There are three types of cation transporting ATPases: oligomycin sensitive F-ATPases, bafilomycin-sensitive V (vacuolar) H⁺-transporting ATPases (V-ATPases) and vanadate-sensitive P (phosphate binding) ATPases (P-ATPases), the most important of these being Ca²⁺-ATPase, Na⁺/K⁺-ATPase and H⁺/K⁺-ATPase. The influences of numerous modulators are reviewed.     

不同生境人参茎叶总皂苷对心律失常小鼠的作用比较

目的 探讨园参茎叶总皂苷(GSLS)和林下山参茎叶总皂苷(MSLS)对心律失常小鼠的改善作用.方法 将80只SPF级BALB/c小鼠随机分为正常组、模型组、园参茎叶总皂苷低(GSLS-L)、中(GSLS-M)、高(GSLS-H)剂量组、林下山参茎叶总皂苷低(MSLS-L)、中(MSLS-M)、高(MSLS-H)剂量组....     

Lipoic acid blocks seizures induced by pilocarpine via increases in δ-aminolevulinic dehydratase and Na, K-ATPase activity in rat brain

In the present study we investigated the effects of lipoic acid (LA) on δ-aminolevulinic dehydratase (δ-ALA-D) and Na⁺, K⁺-ATPase activities in rat brain after seizures induction by pilocarpine. Wistar rats were treated with 0.9% saline (i.p., control group), lipoic acid (10 mg/kg, i.p., LA group), pilocarpine (400 mg/kg, i.p., pilocarpine group), or the combination of LA (10 mg/kg, i.p.) with pilocarpine (400 mg/kg, i.p.), 30 min before administration of LA (LA plus pilocarpine group). After the treatments all groups were observed for 1 h. The enzyme activities (δ-ALA-D and Na⁺, K⁺-ATPase) were measured using spectrophotometric methods, and the results were compared with that obtained from saline and pilocarpine-treated animals. Neuroprotective effects of LA against seizures were evaluated based on those enzyme activities. The pilocarpine group showed a reduction in δ-ALA-D and Na⁺, K⁺-ATPase activities after seizures. In turn, LA plus pilocarpine abolished the appearance of seizures and reversed the decreased in δ-ALA-D and Na⁺, K⁺-ATPase activities produced by seizures, when compared to the pilocarpine seizing group. The results from the present study demonstrate that preadministration of LA abolished seizure episodes induced by pilocarpine in rat, probably by increasing δ-ALA-D and Na⁺, K⁺-ATPase activities in rat brain during seizures.     

Study of antidepressant-like activity of an enriched phloroglucinol fraction obtained from Hypericum caprifoliatum

Context: Hypericum caprifoliatum Cham &; Schlecht (Guttiferae) extracts have a potential antidepressant-like effect in rodents. However, the molecular mechanisms by which these extracts exert this effect remain unclear.

Objective: This study evaluated the effect of HC1, a fraction obtained from H. caprifoliatum enriched in phloroglucinol derivatives, on the Na⁺, K⁺ ATPase activity in mouse brain and verified the influence of veratrine on the effect of HC1 in the forced swimming test (FST).

Materials and methods: Veratrine (0.06?mg/kg) and HC1 (360?mg/kg) were given alone or combined i.p. 60 and p.o. 30?min, respectively, before FST. The effect of single and repeated administration (once a day for 3 consecutive days) of HC1 (360?mg/kg) on Na⁺, K⁺ ATPase activity was evaluated ex vivo in the cerebral cortex and hippocampus of mice subjected or not to FST.

Results: HC1 reduced the immobility time (103.15?±?18.67?s), when compared to the control group (183.6?±?9.51?s). This effect was prevented by veratrine (151.75?±?22.19?s). Mice repeatedly treated with HC1 presented a significant increase in Na⁺, K⁺ ATPase activity, both in cerebral cortex (46?±?2.41?nmol Pi/min?mg protein) and hippocampus (49.83?±?2.31?nmol Pi/min?mg protein), in relation to the respective controls (30?±?2.66 and 29.83?±?2.31?nmol Pi/min?mg protein respectively).

Discussion and conclusion: The HC1 antidepressant-like effect on FST might be related to its capacity to inhibit Na⁺?influx. HC1 increases hippocampal and cortical Na⁺, K⁺ ATPase activities possibly through long-term regulatory mechanisms.     

Neurochemical changes on oxidative stress in rat hippocampus during acute phase of pilocarpine-induced seizures

Using the epilepsy model obtained by systemic administration of pilocarpine in rats in the present study we investigated the changes caused by seizures on content and species of gangliosides and phospholipids, as well as on cholesterol concentration, glutathione reduced contents, Na⁺, K⁺-ATPase activity and lipid peroxidation levels in rat hippocampus. Wistar rats received pilocarpine hydrochloride (400 mg/kg, i.p., pilocarpine group), and other group received 0.9% saline (i.p., control group). Results showed that seizures significantly decreased the total content of lipids and glutathione reduced concentration in rat hippocampus. We also observed that seizures significantly reduced the absolute quantity of the major brain gangliosides (GM1, GD1a, GD1b and GT1b) and phospholipids (sphingomyelin, phosphatidylcholine and phosphatidylethanolamine). Our data also showed a decreased Na⁺, K⁺-ATPase activity and an increased TBARS levels in hippocampus of seized rats. If confirmed in human beings, these data could suggest that the alteration in lipid composition, Na⁺, K⁺-ATPase activity, glutathione reduced content and TBARS levels caused by seizures might contribute to the neurophysiopathology of seizures observed in epileptic patients.     

Effects of adult-onset choline deprivation on the activities of acetylcholinesterase, (Na,K)- and Mg-ATPase in crucial rat brain regions

Choline (Ch) plays an important role in brain neurotransmission, while Ch-deprivation (CD) has been linked to various pathophysiological states. Prolonged ingestion of Ch-deficient diet (CDD) is known to produce CD causing a reduction of rat brain acetylcholine (ACh) levels, as well as memory and growth disorders. The aim of this study was to investigate the effect of a 2-month adult-onset CD on the activities of acetylcholinesterase (AChE), (Na⁺,K⁺)- and Mg²⁺-ATPase in crucial brain regions of male rats. Adult rats were divided into two groups (control and CD). The CD group was fed with CDD for 2-months. At the end of the second month, rats were sacrificed by decapitation and the brain regions were rapidly removed. Enzyme activities were measured spectrophotometrically in the homogenated frontal cortex, hippocampus, hypothalamus, cerebellum, and pons. In CD rats, AChE activity was found statistically significantly increased in the hippocampus and the cerebellum (+28%, P < 0.001 and +46%, P < 0.001, respectively, as compared to control), while it was found unaltered in the other three regions (frontal cortex, hypothalamus and pons). (Na⁺,K⁺)-ATPase activity was found increased by CD in the frontal cortex (+30%, P < 0.001), decreased in both hippocampus and hypothalamus (−68%, P < 0.001 and −51%, P < 0.001, respectively), and unaltered in both cerebellum and pons. No statistically significant changes were observed in the activities of Mg²⁺-ATPase in the frontal cortex and the hypothalamus, while statistically significant increases were recorded in the hippocampus (+21%, P < 0.01), the cerebellum (+85%, P < 0.001) and the pons (+19%, P < 0.05), as compared to control levels. Our data suggest that adult-onset CD can have significant effects on the examined brain parameters in the examined crucial brain regions, as well as that CD is a metabolic disorder towards which different and brain region specific neurophysiological responses seem to occur. Following a 2-month adult-onset CD, the activity of AChE was found to be increased in the hippocampus and the cerebellum and unaltered in the other three regions (frontal cortex, hypothalamus and pons), while Na⁺,K⁺-ATPase activity was found to be increased in the frontal cortex, decreased in both hippocampus and hypothalamus, and unaltered in both cerebellum and pons. Moreover, Mg²⁺-ATPase activity was found to be unaltered in the frontal cortex and the hypothalamus, and increased in the hippocampus, the cerebellum and the pons. The observed differentially affected activities of AChE, (Na⁺,K⁺)-ATPase and Mg²⁺-ATPase (induced by CD) could result in modulations of cholinergic neurotransmission, neural excitability, metabolic energy production, Mg²⁺ homeostasis and protein synthesis (that might have a variety of neurophysiological consequences depending on the brain region in which they seem to occur).     

Effect of heparin treatment on the expression and activity of different ion-motive P-type ATPase isoforms from mouse extensor digitorum longus muscle during degeneration and regeneration after Bothrops jararacussu venom injection

Ca²⁺ ions are essential to myonecrosis, a serious complication of snake envenomation, and heparin seems to counteract this effect. We investigated the effect of local injection of Bothrops jararacussu venom in mouse fast-twitch extensor digitorum longus (EDL) muscle, without or with heparin, on functional/molecular alterations of two central proteins involved in intracellular Ca²⁺ homeostasis, sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) and Na⁺/K⁺-ATPase. EDL-specific SERCA1 isoform expression dropped significantly just after venom administration (up to 60% compared to control EDL values at days 1 and 3; p < 0.05) while SERCA2 and Na⁺/K⁺-ATPase α₁ isoform expression increased at the same time (3-6- and 2-3-fold, respectively; p < 0.05). Although not significant, Na⁺/K⁺-ATPase α₂ isoform followed the same trend. Except for SERCA2, all proteins reached basal levels at the 7th day. Intravenous heparin treatment did not affect these profiles. Ca²⁺-ATPase activity was also decreased during the first days after venom injection, but here heparin was effective to reinstate activity to control levels within 3 days. We also showed that B. jararacussu venom directly inhibited Ca²⁺-ATPase activity in a concentration-dependent manner. Our results indicate that EDL SERCA and Na⁺/K⁺-ATPase are importantly affected by B. jararacussu venom and heparin has protective effect on activity but not on protein expression.     

Evidence against a regulation of Na+/K+-ATPase by Gi proteins. Failure to detect an influence of G proteins on Na+/Ca2+-exchange in cardiac sarcolemmal membranes

In the myocardium the inhibitory guanine nucleotide-binding regulatory proteins (G_i proteins) mediate negative chronotropic and negative inotropic effects by activation of K⁺ channels and inhibition of adenylyl cyclase. The concept of a uniform inhibitory action of G_i proteins on myocardial cellular activity has been questioned by the recent observations of adenosine-induced activation of the Na⁺/Ca²⁺ exchange and a carbachol-induced inhibition of the Na⁺/K⁺-ATPase activity in cardiac sarcolemmal membranes. The aim of the present study, therefore, was to reinvestigate the putative regulation of Na⁺/Ca²⁺ exchange and Na⁺/K⁺-ATPase activity in purified canine sarcolemmal membranes. These membranes were enriched in adenosine A₁ (Maximum number of receptors, B _max 0.033 pmol/mg) and muscarinic M₂ (B _max 2.9 pmol/mg) receptors and contained G_i2 and G_i3, two G_i protein isoforms, and Go, another pertussis toxin-sensitive G protein, as detected with specific antibodies. The adenosine A₁-selective agonist, (–)-N ⁶-(2-phenylisopropyl)-adenosine, and the muscarinic agonist, carbachol, both inhibited isoprenaline-stimulated adenylyl cyclase activity by 25% and 35% respectively, and the stable GTP analogue 5-guanylylimidodiphosphate inhibited forskolin-stimulated adenylyl cyclase activity by 35% in these membranes. The characteristics of Na⁺/Ca²⁺ exchange and Na⁺/K⁺-ATPase activity as well as those of the ouabain-sensitive, K⁺-activated 4-nitrophenylphosphatase, an ATP-independent, partial reaction of the Na⁺/K⁺-ATPase, were in agreement with published data with regard to specific activity, time course of activity and substrate dependency. However, none of these activities were influenced by adenosine, (–)-N ⁶-(2-phenylisopropyl)-adenosine, carbachol, or stable GTP analogs, suggesting that Na⁺/Ca²⁺ exchange and Na⁺/K⁺-ATPase are not regulated by Gi proteins in canine cardiac sarcolemmal membranes.     

Inhibition of human colonic (Na++K+)-ATPase by arachidonic and linoleic acid

Summary The sodium pump, (Na⁺+K⁺)-ATPase, which is involved in the transport of cations and water movement by the colonic mucosa, may be decreased in various diarrhoeal states. In this study, we have measured ³H-ouabain binding and (Na⁺+K⁺)-ATPase activity in human colonic biopsy homogenates and the influence of various inflammatory and antiinflammatory compounds on these parameters. ³H-ouabain binds to one site of high affinity (K _D 1.9±0.2×10^–9 mol/l) with a maximal binding capacity of 7.5±0.8×10¹⁴ binding sites/g protein. Both arachidonic and linoleic acid inhibited (Na⁺+K⁺)-ATPase activity (IC₅₀ arachidonic acid: 7.5×10^–5 mol/l, linoleic acid: 6.5×10^–5 mol/l) and Mg²⁺-ATPase activity (IC₅₀ arachidonic acid: 9×10^–5 mol/l, linoleic acid: 4×10^–5 mol/l). Arachidonic acid inhibited ³H-ouabain binding, (IC₅₀ 3.2×10^–5 mol/l). The following antiinflammatory compounds, at concentrations up to 1×10^–3 mol/l, did not influence ATPase activity directly nor reverse the arachidonic acid-induced inhibition: indomethacin (cyclooxygenase inhibitor), nordihydroguaretic acid (lipoxygenase inhibitor), sulphasalazine and its metabolites: 5-aminosalicylic acid, N-acetylaminosalicylic acid and sulphapyridine.These results indicate that human colonic (Na⁺+K⁺)-ATPase is inhibited by the prostanoid precursors, arachidonic and linoleic acid. From a therapeutic point of view (effect on colonic (Na⁺+K⁺)-ATPase and perhaps diarrhoea), the suppression of the production of these prostanoid precursors by drugs may, therefore, be beneficial in the treatment of inflammatory bowel disease.Supported by DFG (Er65/4-4)     

柴胡皂甙和甘草甜素抑制Na+,K+-ATP酶活性的构效关系

研究在离体条件下各种单体柴胡皂甙和甘草甜素抑制Na⁺,K⁺-ATP酶活性的构效关系。实验结果表明,各种柴胡皂甙抑制Na⁺,K⁺-ATP酶活性的作用强度依次为:b₁>d>b₂>b₄>a>b₃>e>c。柴胡皂甙化学结构中的C₂₃-OH,C₁₆-OH及C₁₁和C₁₃的共轭双烯可能对其抑制活性起重要作用。甘草甜素(GL),甘草次酸(GA)和生胃酮(18-β-甘草次酸半琥珀酸双钠盐,CX)抑制Na⁺,K⁺-ATP酶活性的作用强度依次为GA≥CX>GL。研究还证明,柴胡皂甙d对Na⁺,K⁺-ATP酶的抑制为非竟争性抑制。     

Behavior and brain enzymatic changes after long-term intoxication with cadmium salt or contaminated potatoes

This study investigated the cadmium (Cd) intoxication on cognitive, motor and anxiety performance of rats subjected to long-term exposure to diet with Cd salt or with Cd from contaminated potato tubers. Potato plantlets were micropropagated in MS medium and transplanted to plastic trays containing sand. Tubers were collected, planted in sand boxes and cultivated with 0 or 10 μM Cd and, after were oven-dried, powder processed and used for diet. Rats were divided into six groups and fed different diets for 5 months: control, potato, potato + Cd, 1, 5 or 25 mg/kg CdCl₂. Cd exposure increased Cd concentration in brain regions. There was a significant decrease in the step-down latency in Cd-intoxicated rats and, elevated plus maze task revealed an anxiolytic effect in rats fed potato diet per se, and an anxiogenic effect in rats fed 25 mg/kg Cd. The brain structures of rats exposed to Cd salt or Cd from tubers showed an increased AChE activity, but Na⁺,K⁺-ATPase decreased in cortex, hypothalamus, and cerebellum. Therefore, we suggest an association between the long-term diet of potato tuber and a clear anxiolytic effect. Moreover, we observed an impaired cognition and enhanced anxiety-like behavior displayed by Cd-intoxicated rats coupled with a marked increase of brain Cd concentration, and increase and decrease of AChE and Na⁺,K⁺-ATPase activities, respectively.     

Inhibition of Na+, K+-ATPase in rat renal proximal tubules by dopamine involved DA-1 receptor activation

Summary Endogenous kidney dopamine (DA) causes natriuresis and diuresis, at least partly, via inhibition of proximal tubular Na⁺,K⁺-ATPase. The present study was done to identify the dopamine receptor subtype(s) involved in dopamine-induced inhibition of Na⁺,K⁺-ATPase activity. Suspensions of renal proximal tubules from Sprague-Dawley rats were incubated with dopamine, the DA-1 receptor agonist fenoldopam or the DA-2 receptor agonist SK&F 89124 in the presence or absence of either the DA-1 receptor antagonist SCH 23390 or the DA-2 receptor antagonist domperidone. Dopamine and fenoldopam (10^–5 to 10^–8 mol/1) produced a concentration-dependent inhibition of Na⁺,K⁺-ATPase activity. However, SK&F 89124 failed to produce any significant effect over the same concentration range. Incubation with fenoldopam (10^–5 to 10^–8 mol/1) in the presence of SK&F 89124 (10^–6 mol/l) inhibited Na+,K+-ATPase activity to a degree similar to that with fenoldopam alone. Furthermore, DA-induced inhibition of Na⁺,K⁺-ATPase activity was attenuated by SCH 23390, but not by domperidone. Since -adrenoceptor activation is reported to stimulate Na⁺,K⁺-ATPase activity and, at higher concentrations, dopamine also acts as an a-adrenoceptor agonist, the potential opposing effect from -adrenoceptor activation on DA-induced inhibition of Na⁺,K⁺-ATPase activity was investigated by using the -adrenoceptor blocker phentolamine. We found that, in the lower concentration range (10^–5 to 10^–7 mol/1), dopamine-induced inhibition of Na⁺,K⁺-ATPase activity in the presence of phentolamine was similar in magnitude to that observed with dopamine alone. However, at the highest concentration used (10^–4 mol/1), dopamine produced a significantly larger degree of inhibition of Na⁺,K⁺-ATPase activity in the presence of phentolamine. These results indicate that the DA-1 dopamine receptor subtype, but not the DA-2 receptor subtype, is involved in dopamine-mediated inhibition of Na⁺,K⁺-ATPase. At higher concentrations of dopamine, the DA-1 receptor-mediated inhibitory effect on Na⁺,K⁺-ATPase activity may be partly opposed by a simultaneous -adrenoceptor-mediated stimulation of the activity of this enzyme.     

Palytoxin binds to and inhibits kidney and erythrocyte Na+, K+-ATPase

Summary Hog kidney Na⁺, K⁺-ATPase, purified to the microsomal stage and activated with detergent, binds palytoxin, as shown by the nearly complete competition of the toxin with ³H-ouabain. The K _i-values of palytoxin, but not of ouabain, depend on the protein concentration; this indicates additional binding sites for the toxin on kidney membranes. — Palytoxin inhibits the enzymatic activity of the detergent-activated preparation nearly completely (IC₅₀ 8·10^–7 mol/l). Inhibition of ATPase activity and of ouabain binding are promoted by borate, a known activator of palytoxin. — Palytoxin also inhibits the Na⁺, K⁺-ATPase of erythrocyte ghosts in the same dose range.The data are discussed in context with the hypothesis (Chhatwal et al. 1983) that palytoxin raises the cellular permeability by altering the state of Na⁺, K⁺-ATPase or its environment.Part of the thesis (Dr. rer. nat.) of H. Böttinger     

Insulin induced translocation of Na^＋/K^＋-ATPase is decreased in the heart of streptozotocin diabetic rats

Aim:

To investigate the effect of acute insulin administration on the subcellular localization of Na⁺/K⁺-ATPase isoforms in cardiac muscle of healthy and streptozotocin-induced diabetic rats.

Methods:

Membrane fractions were isolated with subcellular fractionation and with cell surface biotinylation technique. Na⁺/K⁺-ATPase subunit isoforms were analysed with ouabain binding assay and Western blotting. Enzyme activity was measured using 3-O-methylfluorescein-phosphatase activity.

Results:

In control rat heart muscle α1 isoform of Na⁺/K⁺ ATPase resides mainly in the plasma membrane fraction, while α2 isoform in the intracellular membrane pool. Diabetes decreased the abundance of α1 isoform (25 %, P<0.05) in plasma membrane and α2 isoform (50%, P<0.01) in the intracellular membrane fraction. When plasma membrane fractions were isolated by discontinuous sucrose gradients, insulin-stimulated translocation of α2- but not α1-subunits was detected. α1-Subunit translocation was only detectable by cell surface biotinylation technique. After insulin administration protein level of α2 increased by 3.3-fold, α1 by 1.37-fold and β1 by 1.51-fold (P<0.02) in the plasma membrane of control, and less than 1.92-fold (P<0.02), 1.19-fold (not significant) and 1.34-fold (P<0.02) in diabetes. The insulin-induced translocation was wortmannin sensitive.

Conclusion:

This study demonstrate that insulin influences the plasma membrane localization of Na⁺/K⁺-ATPase isoforms in the heart. α2 isoform translocation is the most vulnerable to the reduced insulin response in diabetes. α1 isoform also translocates in response to insulin treatment in healthy rat. Insulin mediates Na⁺/K⁺-ATPase α1- and α2-subunit translocation to the cardiac muscle plasma membrane via a PI3-kinase-dependent mechanism.     

Gastric acid secretion in the dog: a mechanism-based pharmacodynamic model for histamine stimulation and irreversible inhibition by omeprazole

A mechanism-based pharmacodynamic model was used to describe the inhibitory effect by omeprazole on gastric acid secretion measured after histamine stimulation in the dog. The model identifies parameters that are related to the physiological system, the histamine stimulation, and the irreversible effect of omeprazole on the H⁺, K⁺-ATPase enzyme. Four different experiments with omeprazole (Exps. 1–4) and two placebo experiments were performed in each of the four Heidenhain pouch dogs used. For placebo and experiments 1–3, saline or omeprazole 0.81 mol/kg was infused during 3 hr with measurements of histamine-stimulated gastric acid secretion in two periods of 3.5–6.5 hr, one period starting just before the omeprazole infusion and a second later period up to 29 hr post infusion. In experiment 4, 0.18 mol/kg of omeprazole was infused for 22.5 min and gastric juice was collected for 5 hr post infusion. The response data was well described by the model. Similar parameter estimates were obtained by three different analysis methods; naïve pooling, two-stage method and nonlinear mixed effects modeling. The elimination rate constant for the H⁺, K⁺-ATPase enzyme, k _out, was estimated to be 0.040 hr^-1, corresponding to a half-life of about 17 hr. This rate constant determines the duration of omeprazole inhibition after long-term exposure. For short-term omeprazole exposure the duration is determined by the rate constant for transfer of enzymes from active to resting state, estimated to be 1.88 hr^-1. The second-order rate constant for histamine stimulation was estimated to be 0.064 hr^-1 per histamine concentration unit and the maximum acid secretion was estimated to be 5.0 mmol H⁺/30 min. The second-order rate constant for the irreversible binding of omeprazole to H⁺, K⁺-ATPase, k _ome, was estimated to be 2.39 L/mol hr. By modeling the histamine-induced baseline response simultaneously with active treatment, predictions of the response are possible not only following different dosing regimens of omeprazole, but also following different degrees of histamine stimulation.     

Specific activity and sensitivity to strophanthin of the Na+ + K+-activated ATPase in rats and guinea-pigs with hypoadrenalism

Summary In adrenalectomised rats and in guinea-pigs pretreated with metyrapone the specific activity of the Na⁺ + K⁺-stimulated ATPase of heart and kidney is significantly diminished, whereas the activity of the Mg⁺⁺-ATPase remains unchanged. The specific activity of the Na⁺ + K⁺-stimulated ATPase from brain tissue is not influenced by either adrenalectomy or by treatment with metyrapone.The sensitivity of the Na⁺ + K⁺-stimulated ATPase of heart, brain and kidney to k-strophanthin remains unchanged by adrenalectomy or by treatment with metyrapone.Supported by the Deutsche Forschungsgemeinschaft (SFB 30, Kardiologie).     

Na+/K+-ATPase α subunits as new targets in anticancer therapy

Background: The sodium pump (Na⁺/K⁺-ATPase) could be a target for the development of anticancer drugs as it serves as a signal transducer, it is a player in cell adhesion and its aberrant expression and activity are implicated in the development and progression of different cancers. Cardiotonic steroids (CS) are the natural ligands and inhibitors of the sodium pump and this supports the possibility of their development as anticancer agents targeting overexpressed Na⁺/K⁺-ATPase α subunits. Objectives: To highlight and further develop the concept of using Na⁺/K⁺-ATPase α1 and α3 subunits as targets in anticancer therapy and to address the question of the actual usefulness of further developing CS as anticancer agents. Conclusions: Targeting overexpressed Na⁺/K⁺-ATPase α subunits using novel CS might open a new era in anticancer therapy and bring the concept of personalized medicine from aspiration to reality. Clinical data are now needed to further support this proposal. Furthermore, future medicinal chemistry should optimize new anticancer CS to target Na⁺/K⁺-ATPase α subunits with the aim of rendering them more potent and less toxic.     

Studies on the disposition of Li+ in the guinea-pig and rat

Rats or guinea-pigs were given LiCl acutely (2 mmol/kg IP or intragastrically) or chronically (daily doses 0.6–4 mmol/kg) and plasma, erythrocytes, kidney, liver and brain were analysed for Li⁺. Generally, after acute LiCl, tissue Li⁺ levels followed changes in plasma Li⁺ levels. However, brain Li⁺ concentrations changed more slowly and in the rat, but not in the guinea-pig, paralleled erythrocyte Li⁺ concentrations. Li⁺ was absorbed more slowly from the gastrointestinal tract of the rat. After chronic LiCl, the erythrocyte: plasma Li⁺ ratio was about 0.1 in the guinea-pig and about 2 in the rat. Relative Li⁺ tissue concentrations were as follows: guinea-pig, plasma>kidney>liver>brain> erythrocyte; raterythrocyte=brain>liver=plasma. A Na⁺-dependent Li⁺ efflux was demonstrated in the erythrocytes of the guinea-pig and human, but not the rat. This process was inhibited by phloretin (0.2 mM), but not frusemide (2.0 mM). The marked differences in the activity of the erythrocyte Na⁺-dependent Li⁺ countertransport process in the guinea-pig and rat could extend to other tissues and explain the observed interspecies differences in tissue Li⁺ distribution.     

Cardiac glycosides: Correlations among Na+, K+-ATPase,sodium pump and contractility in the guinea pig heart

Summary Relationships among positive inotropic response to cardiac glycosides, Na⁺,K⁺-ATPase inhibition and monovalent cation pump activities were studied using paced Langendorff preparations of guinea-pig heart. Na⁺,K⁺-ATPase activity was estimated from the initial velocity of (³H)-ouabain binding in ventricular homogenates, and cation pump activity from ouabain-sensitive ⁸⁶Rb uptake of ventricular slices. These parameters were assayed in control, ouabain- or digitoxintreated hearts either at the time of inotropic response to the cardiac glycosides or during the course of drug washout. Development and loss of the inotropic response during ouabain or digitoxin perfusion and washout was accompanied by reduction and subsequent recovery of the initial ouabain binding velocity, respectively. If homogenates from glycoside-treated hearts were incubated at 37°C for 10 min during ouabain-binding studies, the levels of binding were not different from those of control hearts, indicating a rapid dissociation of the glycosides from cardiac Na⁺,K⁺-ATPase in this species. Despite differences in the time course of the loss of inotropic responses produced by ouabain or digitoxin, the relationship between Na⁺,K⁺-ATPase inhibition and inotropic responses were similar. Inotropic responses to digitoxin during perfusion, and subsequent los during washout, also were accompanied by a reduction and subsequent recovery of ⁸⁶Rb uptake. A correlation between inhibition of cation pump activity and positive inotropy has hitherto not been demonstrated. Thus, it appears that with cardiac glycosides, a relationship exists among contractility, cardiac Na⁺,K⁺-ATPase and monovalent cation pump activities.