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Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study examined the effects of diet and treatment with noradrenergic receptor antagonists on weight gain and indices of Na+-K+-adenosine triphosphatase (ATPase) activity in the rat. When rats were fed a palatable cafeteria diet, their caloric consumption increased by about 80%, but they did not gain weight significantly. Ouabain binding and K+-p-nitrophenylphosphatase (NPPase) activity were increased in brown adipose tissue and soleus. These indices remained elevated after the rats were returned to a regular diet. When rats were fasted for 3 days, they lost weight, and the indices of Na+-K+-ATPase activity were markedly reduced in brown adipose tissue and soleus. After refeeding the fasted rats gained weight three times more rapidly than nonfasted rats with similar food intake. Indices of Na+-K+-ATPase activity remained as low as they had been when the rats were fasting. There was a consistent negative correlation between weight gain per calorie eaten and brown adipose tissue NPPase activity. Changes in Na+-K+-ATPase could therefore be involved in the effects of overfeeding and fasting on metabolic efficiency. Desmethylimipramine binding was increased by cafeteria diet and decreased by fasting, consistent with changes in sympathetic nervous system activity. Treatment with prazosin, an alpha 1-noradrenergic receptor antagonist, reduced Na+-K+-ATPase in either control or cafeteria diet-fed rats but did not alter the effect of cafeteria diet feeding. By contrast, treatment with propranolol, a beta-receptor antagonist, prevented the increase in Na+-K+-ATPase during cafeteria diet feeding.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Caloric intake and Na+-K+-ATPase: differential regulation by alpha 1- and beta-noradrenergic receptors. 608 94

Kinetic analyses of the Na+-K+-adenosine triphosphatase (ATPase) system were performed in brain and heart preparations from young mature (4 mo old) and healthy aged (25 mo old) rats. The K+-activated p-nitrophenylphosphatase (K+-pNPPase) method was used to assess activity of the enzyme system. Ouabain inhibition of K+-pNPPase activity was also examined. A significant age-related decrease in maximal velocity (Vmax) was found in cardiac K+-pNPPase activity, but no changes were seen in the K+ concentration for half-maximal velocity (K0.5). No age differences in Vmax or K0.5 were seen for brain. No differences in ouabain inhibition were found in either brain or heart. In a second experiment, the major component of the age-related decline in cardiac K+-pNPPase activity was found to occur between 5 and 14 mo of age, a period during which plasma thyroxine had previously been found to decline in the same animals. Since peripheral Na+-K+-ATPase activity is partly thyroid hormone dependent, the age-dependent decrease in cardiac enzyme activity appears to be secondary to neuroendocrine changes.
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PMID:Kinetic studies of the Na+-K+-ATPase enzyme system in brain and heart of aging rats. 609 4

Central cardiovascular effects of the sodium-potassium adenosine triphosphatase (Na+, K+-ATPase) inhibitor, ouabain, were investigated by injecting it intracerebroventricularly (ICV) using conscious Wistar rats. Ouabain, 0.1-10 micrograms injected ICV, produced dose-related pressor responses attaining peak elevations after about 5 min. To investigate the underlying mechanisms of these central pressor responses, angiotensin II blockers were injected ICV before the injections of ouabain. 1-Sar, 8-Ile angiotensin II (ang IIa), 50 micrograms, given 3 min before the ouabain, abolished the pressor responses to ouabain, 5 micrograms. Angiotensin I converting enzyme inhibitor (CEI, captopril), 100 micrograms, also significantly attenuated the pressor responses to ouabain. Since previous results with ICV injections of ouabain suggested that the pressor responses are mediated via a release of brain angiotension II, and the site of action of brain angiotensin II is believed to be the anteroventral third ventricle (AV3V) area of the brain, ICV injections of ouabain were repeated using rats whose AV3V areas had been destroyed electrically. The pressor responses were smaller in the AV3V lesioned rats than in sham-operated rats. The abdominal sympathetic nerve activity was recorded using three conscious, normotensive Wistar rats. ICV injections of ouabain, 5 micrograms, elicited pressor responses as described above and these were accompanied by a corresponding increase in the nerve firing, lasting for 5-7 min. These responses were again abolished by pretreatment with an angiotensin II antagonist. These results suggest that centrally administered ouabain elicits vasopressor responses which increase peripheral sympathetic nerve activity.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Centrally-induced vasopressor responses to sodium-potassium adenosine triphosphatase inhibitor, ouabain, may be mediated via angiotensin II in the anteroventral third ventricle in the brain. 609 53

The effects of ouabain and other cardiotonic steroids were examined to investigate whether changes in Na,K-adenosine triphosphatase (ATPase) activity modified the actions of palytoxin (PTX) in rabbit aortic vascular smooth muscle. The effects of these agents on rabbit aorta were compared with those on rat aorta, as it is known that the concentration of cardiac glycosides required to inhibit Na,K-ATPase of rat aorta is markedly higher than that of other species. PTX induced contraction in rabbit and rat aortas in a similar concentration range (10(-11) to 10(-8) M). PTX rapidly decreased tissue K content of these preparations. Ouabain (2 X 10(-5) M) inhibited both the contraction and the loss of tissue K in rabbit aorta but not in rat aorta. In rabbit aorta, convallatoxin (2 X 10(-5) M), which has one rhamnose as a sugar moiety like ouabain, and cymarin (2 X 10(-5) M), which has one cymarose, inhibited the PTX-induced contraction and the loss of tissue K, although ouabagenin, convallatoxigenin and cymarigenin (strophanthidin) (2 X 10(-5) M) did not. Other cardiotonic steroids, digoxin and digitoxin, which have 3 U of digitoxose as a sugar component, or the corresponding aglycones failed to inhibit the PTX-responses. On the other hand, all the cardiotonic steroids at concentration of 2 X 10(-5) M equally inhibited the reuptake of K and relaxation of norepinephrine-induced contractions induced by the readdition of K. Inhibition of Na-K pump by K-free solution potentiated rather than inhibited the PTX-induced contraction. These results suggest that the specific sugar moiety of cardiac glycosides is important for the inhibitory effect exerted by these compounds on the PTX-induced responses and that the inhibition is not related to the activity of the Na,K-ATPase.
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PMID:Involvement of the sugar moiety in the inhibitory action of the cardiac glycosides on the palytoxin-induced responses in vascular smooth muscles. 614 1

1 Secretion of catecholamines (CA) evoked by ouabain, chlormadinone acetate (CMA), phenoxybenzamine (Pbz) and vanadate, four agents known to inhibit Na(+), K(+)-dependent Mg(2+)-activated adenosine triphosphatase (ATPase) activity has been studied in suspensions of bovine isolated adrenal medullary cells.2 Acetylcholine (ACh) evoked a 5 fold increase of the basal CA secretion from isolated cells suspended in oxygenated Krebs-bicarbonate solution kept at 27 degrees C. Secretion was antagonized by Ca(2+)-deprivation or hexamethonium, indicating good functional viability of the cells.3 Ouabain (10(-7) to 10(-4) M) evoked a progressive, dose-dependent release of CA from cell suspensions. Study of the time course of the secretory response for 2 h allowed the separation of two components in the secretory response at all doses studied: a slow initial component (0.011 pg/min CA) and a second faster component (0.032 pg/min CA).4 CMA evoked a clear-cut CA secretory response. The ED(50) for CMA was 10(-4) M, as compared to 3 x 10(-6) M for ouabain. Pbz and vanadate did not induce CA release.5 [(3)H]-ouabain was taken up and bound to intact isolated cells by a non-saturable binding process. However, in semi-purified plasma membranes from bovine adrenal medulla a saturable specific [(3)H]-ouabain binding process was observed with a K(D) of 8.1 nM. Binding to the membranes was ATP-dependent and antagonized by K(+).6 [(3)H]-ouabain specific binding to membranes was antagonized by ouabain and CMA, but not by Pbz or vanadate; the ID(50) for ouabain and CMA were 10(-6) and 10(-5) M respectively.7 Ouabain partially inhibited, in a dose-dependent manner, Na(+), K(+)-Mg(2+) ATPase activity of the semi-purified plasma membranes.8 The results demonstrate a good correlation between the ability of different drugs, known to inhibit ATPase activity, to displace [(3)H]-ouabain binding to adreno-medullary plasma membranes and their capacity to evoke a CA secretory response from isolated chromaffin cells. The data also suggest that the CA secretory effects of ouabain may not be due simply to inhibition of the Na(+) pump and the subsequent ionic redistribution across the plasma membrane; a second mechanism may also be involved.
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PMID:Correlation between catecholamine secretion from bovine isolated chromaffin cells and [3H]-ouabain binding to plasma membranes. 616 27

Isolated atria of guinea-pigs were treated with veratrine until the initial signs of toxicity were seen. Ouabain was then added cumulatively, starting with a threshold inotropic concentration, 50 nM, until the tissue became dysrhythmic. It was found that a concentration of ouabain which by itself gave a positive inotropic effect of only 3%, significantly enhanced the toxicity of veratrine. Veratrine had no effect on the (Na+ + K+)-adenosine triphosphatase ((Na+ + K+)-ATPase) enzyme isolated from guinea-pig ventricle. The conclusion drawn is that at threshold inotropic concentrations of ouabain it is likely that the (Na+ + K+)-ATPase is inhibited rather than stimulated.
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PMID:Enhancement of the toxic effects of veratrine on guinea-pig atrium by threshold inotropic doses of ouabain. 624 31

The effects of thyroid hormone treatment on brown adipose tissue (BAT) and liver metabolism were assessed by measuring oxygen consumption, sodium-potassium adenosine triphosphatase (Na-K-ATPase), and mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) activities in tissues from triiodothyronine- (T3) and vehicle-injected (for 3 days) newborn and adult rabbits. In the newborns, basal BAT cellular respiration was increased [mean (%/- SE) = 119 +/- 18 vs. 65 +/- 4 microliter O2/10(6) cells-1 . h in controls (P less than 0.005)], whereas hepatic respiration was unchanged. Ouabain had no effect on basal BAT cellular respiration, but suppressed hepatic respiration by 30% in both newborn groups. T3 treatment had no effect on NE- (10(-6) M) stimulated BAT respiration, whereas adult hepatic respiration was increased almost twofold. alpha-GPD activities were increased in both newborn BAT and adult liver but not in newborn liver. Na-K-ATPase activity was significantly increased only in newborn liver. In conclusion, 1) both BAT and liver are thyroid-hormone sensitive in the newborn rabbit, but the responses to T3 treatment are different in the two tissues; 2) the failure to stimulate both hepatic alpha-GPD and respiration in the newborn appears to be a developmental phenomenon characteristic of the rabbit; 3) thyroid hormones have little effect on sodium transport-dependent respiration in either BAT of liver in the newborn rabbit.
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PMID:Thyroid hormone-sensitive brown adipose tissue respiration in the newborn rabbit. 627 13

Cumulative addition of vanadate or ouabain to rat liver perfusions giving perfusate concentrations up to about 500 microM revealed that both liver hemodynamics and bile production are influenced by these substances, but their ways of action differed markedly. Vanadate increased hepatic vascular resistance in a dose-dependent manner with an apparent Km of 30 microM. Not until vanadate concentrations in perfusate reached 60 to 70 microM did the hepatic oxygen consumption decrease significantly together with a decrease in bile flow. Ouabain at perfusate concentrations up to nearly 300 microM caused only a slight fall in perfusate flow, a dose-dependent slight fall in oxygen uptake and a dose-dependent, marked increase in bile flow. Further addition of even small amounts of ouabain initiated a marked fall in perfusate flow, oxygen uptake and bile production and appeared to induce maldistribution of intrahepatic perfusate flow. The vasoconstrictive effect of vanadate was not influenced by alpha or beta blockers, atropine or blockers of Ca++-transport, whereas the effect of ouabain could be strongly reduced by phenoxybenzamine or verapamil. Vanadate-induced vasoconstriction may be caused by an inhibition of smooth muscle Ca++-adenosine triphosphatase and ouabain may induce vasoconstriction by inhibiton of smooth muscle Na, K-adenosine triphosphatase. The hepatic uptake and excretion of ouabain may explain the choleresis observed at small perfusate concentrations of ouabain. Inhibition of bile production at higher concentrations of ouabain and vanadate could be secondary to simultaneous changes in liver hemodynamics.
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PMID:Comparison of vanadate and ouabain effects on liver hemodynamics and bile production in the perfused rat liver. 627 35

Several methods of purification of Na+,K+-adenosine triphosphatase (ATPase) have been previously described for a wide variety of tissues. In general, highest activity preparations have necessitated large amounts of tissue and many purification steps. This article describes a technique that allows partial purification of Na+,K+-ATPase from as few as 15 rat brains and should be of interest to investigators of the pharmacology of this particular enzyme system. In this modified version of the Jorgensen procedure (Biochim Biophys Acta 356:36--52, 1974) we purified the Na+,K+-ATPase from 15--90 rat brains, and obtained enzyme preparations with a mean specific activity of 552 +/- 37.6 mumol Pi/mg of protein/hr (95.5% ouabain sensitive). This "purified" enzyme had an activity ratio (Mg2+ + Na+ + K+)/(Mg2+ + Na+) of 47.4 +/- 12.3 SEM, compared to 3.29 +/- 0.17 SEM for the untreated microsomes. Ouabain inhibited the "purified" enzyme with an I50 of 6 X 10(-9) M. Ouabain binding (644 pmol/mg of protein) yielded a turnover number of 13,700 min-1. Sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis of the enzyme revealed predominantly the alpha and beta subunits with some minor contaminant bands. Previous methods of purification of rat brain Na+,K+-ATPase have employed sodium deoxycholate and high concentrations of NaI; the reported specific activity obtained was generally 150--350 mumol Pi/mg of protein/hr. We have employed higher SDS concentrations than in Jorgensen's technique for rabbit kidney but the procedure is simpler because sucrose gradients are not used. Final wash steps also include 10--20% glycerol in the media. These modifications have yielded Na+,K+-ATPase of significantly higher specific activity than previously reported for rat brain.
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PMID:A simple method for the purification of rat brain Na+,K+-adenosine triphosphatase (ATPase). 628 10

Addition of ouabain caused gradual increases of both the Na content of cultured myocardial cells and the rate of Ca++ uptake by the cells. Ouabain-induced irregular beating of the cells (ouabain toxicity) appeared to develop when the Na content and the rate of Ca++ uptake exceeded about 1.5 and 2.0 times, respectively, the normal levels. Quinidine and procainamide prevented ouabain-induced increases of the Na content and the rate of Ca++ uptake as well as ouabain-induced toxicity. The problem of how quinidine and procainamide counteract the effects of ouabain was then studied. Quinidine and procainamide did not affect the Na+-Ca++ exchange activity. Na+,K+-adenosine triphosphatase activity, Na+-pumping out activity or ouabain-binding activity of myocardial cells, but inhibited passive Na+ influx, which is achieved by a simple diffusion system. From these observations, it is suggested that inhibition by quinidine or procainamide of passive Na+ influx indirectly prevents ouabain-induced increase in the intracellular Na content of myocardial cells and that this presumably explains at least in part the inhibitory effect of quinidine and procainamide on ouabain-induced irregular beating.
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PMID:Inhibition of ouabain-induced increase in Na content of cultured myocardial cells by quinidine and procainamide. 629 80


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