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At least 793 records · Page 44Linked to original sources
PubMed1986

Structure-activity relationship of cardiac steroids having a doubly linked sugar and related compounds for the inhibition of Na+,K+-adenosine triphosphatase.

Forty-three different cardiac steroids having a doubly linked sugar and related compounds were tested for inhibition of Na+,K+-adenosine triphosphatase from guinea pig heart, and the structure-activity relationship has been discussed. The doubly linked glycosides showed higher activities than the respective genins. The inhibitory activities of these compounds were also dependent upon the presence of ring C substituents. The bufadienolide rhamnosides exhibited greater than three times the inhibitory activity of the parent genin, while the glucosyl residue exerted no significant activity.

Animals↗
PubMed1998

Erythrocyte and plasma Ca2+, Mg2+ and cell membrane adenosine triphosphatase activity in patients with essential hypertension.

OBJECTIVE: To assess the relationships between plasma and intracellular Ca2+, Mg2+ and blood cell membrane adenosine triphosphatase (ATPase) activity in normotensive and hypertensive subjects. METHODS: Plasma and intracellular Ca2+, Mg2+ were measured with atomic absorption spectrophotometry, and red blood cell membrane Na(+)-K+ ATPase and Ca(2+)-ATPase activities were determined with colorimetric method in 55 patients with essential hypertension and 32 normotensive controls. RESULTS: The results showed that the hypertensive group consistently demonstrated a significant decreased activity of ATPase studied, with significantly lower plasma Ca2+ and higher cytosolic Ca2+ levels when compared with those in normotensive group (P < 0.01 or P < 0.05, respectively). No significant differences were found in either plasma Mg2+ or intracellular Mg2+ level between the two groups. CONCLUSIONS: This study suggests that patients with essential hypertension have widespread depression of cell membrane Na(+)-K(+)-ATPase and Ca(2+)-ATPase activities with plasma Ca2+ depletion and cytosolic Ca2+ overload, which may reflect an underlying membrane abnormality in essential hypertension. The cellular abnormalities may be related to the defective transport mechanisms that in turn may be aggravated by plasma Ca2+ depletion.

Adult↗
PubMed1978

Binding of divalent cation to phosphoenzyme of sodium- and potassium-transport adenosine triphosphatase.

In order to study the action of the divalent cation which is essential for phosphorylation of sodium- and potassium-transport adenosine triphosphatase, magnesium ion, the normal ligand, was replaced with calcium ion, which had properties diffeerent from those of Mg2+, Mn2+, Fe2+, Co2+, Ni2+, or Zn2+. Phosphorylation of the enzyme from ATP at pH 7.4 in the presence of Na+ and Ca2+ yielded a Ca.phosphoenzyme (60% of the maximal level) with a normal rate of dephosphorylation following a chase with unlabeled Ca.ATP (PK = 0.092S-1 at 0 degrees C). In contrast, after a chase by a chelator, namely ethylenediaminetetraacetic acid, 1,2-cyclohexylenedinitrilotetraacetic acid, or ethylene glycol bis-(beta-aminoethyl ether)N,N'-tetraacetic acid, dephosphorylation slowed within 5 s and half of the initial phosphoenzyme remained with a stability about 5-fold greater than normal. Three states of the phosphoenzyme were distinguished according to their relative sensitivity to ADP or to K+ added during a chase. Normally prepared Mg.phosphoenzyme was sensitive to K+ but not to ADP; Ca.phosphoenzyme was sensitive either to ADP or to K+; and the stabilized phosphoenzyme prepared from Ca.phosphoenzyme by addition of a chelator was sensitive neither to ADP nor to K+ nor to both together. Addition of Ca2+ to the stabilized phosphoenzyme restored the reactivity to that of Ca.phosphoenzyme. Addition of Mg2+ to the stabilized phosphoenzyme changed the reactivity to that of Mg.phosphoenzyme. Therefore, this unreactive, stabilized state of the phosphoenzyme appeared to be a divalent cation-free phosphoenzyme. With respect to sensitivity to ouabain, Ca.phosphoenzyme was as sensitive as Mg.phosphoenzyme but calcium-free phosphoenzyme was much less sensitive. It was concluded that the divalent cation required for phosphorylation normally remains tightly bound to the phosphoenzyme and is required for normal reactivity. Calcium ion was almost unique in dissociating relatively easily from the phosphoenzyme. Strontium ion appeared to act similarly to Ca2+.

Animals↗
PubMed1978

Species differences in sodium-potassium adenosine triphosphatase activity in the smooth muscle of the guinea-pig and rat vas deferens.

The acitvities of sodium-potassium-activated adenosine triphosphatase (Na+,K+-activated ATPase) and ouabain-inhibited, sodium-potassium-activated adensoine triphosphatase (Na+,K+-ATPase) in subcellular fractions of guinea-pig and rat vasa deferentia were compared to determine whether the ineffectiveness of ouabain and reduced extracellular potassium in the rat vas deferens observed in the preceding paper occurs because of a relatively low level of Na+,K+-ATPase and/or an insensitivity to ouabain. The results indicate that the specific and total activities of Na+,K+-activated ATPase and Na+,K+-ATPase (i.e., the transport enzyme) in the individual subcellular fractions and in the tissue were higher in the vas deferens of the rat than in the guinea pig. The percentage of inhibition of Na+,K+-activated activity by ouabain (8 x 10(-5) M) varied in the subcellular fractions; it was higher in the guinea-pig (range 31--87%) than in the rat (nonsignificant effect to 40%). A greater percentage of total Na+K+- activated ATPase activity was inhibited in the vas deferens of the guinea pig (56%) than the rat (30%). Differences in the effects of lowered extracellular potassium concentration or ouabain on resting membrane potential (preceding paper) are apparently unrelated to the amount of transport enzyme in the vasa deferentia or the two species, or to its relative sensitivity to ouabain.

Animals↗
PubMed1986

Na-K-adenosine triphosphatase and cation content in the erythrocyte in essential hypertension.

We measured ouabain-sensitive and ouabain-resistant Na-K-adenosine triphosphatase (ATPase) activity in the red cells of 25 normotensive (average mean blood pressure [BP] 90.2 +/- 1.27 mm Hg) and 29 hypertensive subjects (average mean BP 115.3 +/- 2.45 mm Hg). Intracellular Na and K content were measured in 13 of the normotensive and 19 of the hypertensive subjects. All subjects were male, black, of comparable weight, and had not received antihypertensive medications for at least 30 days. Ouabain-sensitive ATPase activity was found significantly lower in the hypertensive than in the control group (140.2 +/- 11 and 97.6 +/- 7.6 nmol/mg/hr, respectively, P = 0.0008), whereas no significant difference in ouabain-insensitive ATPase was observed. Intracellular Na concentration was higher (9.47 vs. 7.24 mmol/L, P = 0.0144), and intracellular K concentration lower (82.8 vs. 88.8 mmol/L, P = 0.0425) in the hypertensive subjects. These results are consistent with diminished activity of the Na-K pump in black males with essential hypertension who have received no treatment.

Blood Pressure↗