A characterization of the ouabain sensitivity of heart microsomal ATPase

Characterization of the stimulation of neuronal Na(+), K(+)-ATPase activity by low concentrations of ouabain

Low concentrations (< 10(?7) M) of ouabain stimulate the activity of Na(+), K(+)-ATPase in whole homogenates of rat brain. The magnitude of this stimulation varies from 5 to 70%. The concentrations of ouabain which induces maximal stimulation is also highly variable and ranges between 10(?9) to 10(?7) M. The ouabain stimulation disappears following 1:50 dilution and 2 h preincubation or freezing and thawing of the membranes or their treatment with deoxycholate. "Aging" of a preparation of ATPase also results in loss of its ability to be stimulated by ouabain but ouabain inhibition is preserved. No stimulation of enzyme activity by ouabain is observed in rat brain microsomal fraction. The ?-adrenergic blocker propranolol does not inhibit the ouabain induced stimulation of ATPase activity. It is suggested that the stimulation of Na(+), K(+)-ATPase activity by low concentrations of cardiac glycosides if a result of either the displacement of an endogenous ouabain-like compound from the enzyme or an indirect effect by changing membrane surrounding environment of the Na(+), K(+)-ATPase.

Nanomolar concentrations of ouabain block ethanol-inducible Na+,K(+)-ATPase activity in brain

The effect of low concentrations of ethanol on Na+,K(+)-ATPase activity, defined as ouabain-inhibitable 86Rb+ (K+) uptake, was investigated in a crude synaptosome preparation which was subject to minimal subcellular fractionation procedures. Moderate (20-30%) but potent (EC50 = 3.8 mM) stimulation of total ouabain (1 mM)-inhibitable K+ uptake by ethanol was observed following incubation periods of up to 20 min. The activity of the ethanol-induced component of K+ uptake was antagonized by nanomolar concentrations of ouabain. Thus, the moderate stimulation of total ouabain-inhibitable K+ uptake by ethanol was attributable to the activation of a component of K+ uptake which was very sensitive (VS; IC50 = 2.8 x 10(-10) M) to inhibition by ouabain. Slightly higher concentrations of ouabain (10(-9) - 10(-6.6) M) stimulated K+ uptake above control (no ethanol or ouabain) in both the absence and presence of ethanol. The selectivity of the VS-ethanol interaction was demonstrated by the lack of any ethanol effect on two other components of ouabain-inhibitable K+ uptake which accounted for inhibition of K+ uptake by concentrations of ouabain above 10(-6.6) M and were defined as sensitive (S; IC50 = 10(-6) M) and insensitive (I; IC50 = 10(-4) M) to ouabain. These results define the ethanol-inducible component of ouabain-inhibitable Na+,K(+)-ATPase activity and promote the view that changes in Na+,K(+)-ATPase-dependent ion translocation may contribute to ethanol intoxication in vivo.

Experimental regional myocardial ischaemia and myocardial uptake of potassium analogues; intercomparison of 42K, 86Rb and 201Tl

The uptake of 42K, 86Rb and 201Tl by non-ischaemic and ischaemic myocardium was determined in rats with coronary artery ligature lasting 10, 30, 60 and 120 min, and in control rats without ischaemia. Whereas the myocardial concentration of 201Tl and 42K in control rats was similar and higher than that of 86Rb, 201Tl was superior to the other two radionuclides due to its significantly higher accumulation in non-ischaemic myocardium and the higher ratio of non-ischaemic to ischaemic radioactivity. The 86Rb accumulation in non-ischaemic myocardium and non-ischaemic/ischaemic ratio began to decrease from its maximum at 10 min. 201Tl, 42K and 86Rb blood levels in intact animals decreased rapidly after intravenous injection to low and nearly stabilized values at 5 min. Na+K+-ATPase activity in the ischaemic myocardium was high in the acutely ischaemic myocardium and decreased to below control levels after 4 h of ischaemia; changes in activity could not influence the low uptake of potassium analogues in fresh ischaemic myocardium.

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.

The sodium pump of erythrocytes from patients with Duchenne muscular dystrophy: effect of ouabain on the active sodium flux and on (Na+, K+)ATPase

Active ion exchanges across erythrocyte membrane from patients with Duchenne muscular dystrophy were studied by two methods: --erythrocyte ghosts (Na+,K+)ATPase activity and its sensibility to ouabain, using an enzymatic method; --active sodium outflux and its sensibility to ouabain using a radioisotopic method. (Na+,K+)ATPase activity and active sodium outflux were decreased in dystrophic patients compared to normal sex- and age-matched controls. Enzymatic activity and active sodium outflux were inhibited by ouabain 10(-4) M in patients and in controls. Inhibition of the active sodium outflux was lower in patients than in controls. The results are discussed in light of the literature.

Erythrocyte ghosts (Na+ + K+) ATPase activity in Duchenne's dystrophy and myotonia

In Duchenne muscular dystrophy the activity of (Na+ + K+)ATPase in erythrocyte ghosts is reduced and its reaction to ouabain is paradoxical both in low sodium and high sodium systems. No such changes were seen in a case of Becker dystrophy, in limb-girdle dystrophy, and in neurogenic atrophy of muscles. In myotonic dystrophy and congenital myotonia the activity of ATPase and its inhibition by ouabain were depressed.

Erythrocyte abnormality in human myopathy

Erythrocyte ghosts isolated from myopathic patients responded to 10(-4) molar ouabain with a dramatic increase in adenosine triphosphatase activity, while identical preparations from normal donors were inhibited by the same drug. These results have been interpreted in terms of a disease-related change in membrane integrity bearing upon function of the transport enzyme.