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Biomedical subjects

E Erdmann

Publications and source records attributed to E Erdmann.

At least 433 records · Page 24Linked to original sources
PubMed1976

Beta-adrenergic receptors in guinea-pig myocardial tissue.

Stereospecific binding sites for (-) [3H]-alprenolol, a beta-adrenergic antagonist, have been identified in guinea-pig myocardial broken cell preparations. The concentration of the sites was 0.3 pmoles per mg of protein and the dissociation constant (at 37 degrees C) 10(-8) M. A close correlation between the ability of various beta-adrenergic antagonists to compete with tracer alprenolol binding and to block the response of isoprenaline-stimulated myocardial adenylate cyclase has been found. Low affinity sites for the labelled beta-adrenergic antagonist in contrast to stereospecific sites are heat stable and do not discriminate between the (-) and the (+) forms of the beta-adrenergic antagonists. Adenylate cyclase in guinea-pig myocardial tissue is poorly stimulated by isoprenaline or 5'-guanylylimidodiphosphate. This is attributed to a high basal activity which could be lowered by a preincubation at 37 degrees C.

Adenylyl Cyclases↗
PubMed1976

The cardiac glycoside receptor: its properties and its correlation to nucleotide binding sites, phosphointermediate, and (Na++K+)-ATPase activity.

Binding of ouabain to its receptor is followed by a directly proportional inhibition of (Na++K+)-ATPase. The stoichiometry of nucleotide binding site, phosphate acceptor site, ouabain binding site in (Na++K+)-ATPase is 1:1:1. Inactivation of (Na++K+)-ATPase by S-[2,4-Dinitrophenyl]-6-mercaptopurine riboside-5'-triphosphate, which probably forms a thioether derivative of ATP with the enzyme, results in the appearance of a low affinity binding site. It is concluded that the covalently bound ATP fixes the enzyme in a E1 conformational state which is characterized by a low affinity for ouabain.

Adenosine Diphosphate↗
PubMed1976

On the action of triamterene on isolated cell membranes.

Recently there have been recurring reports on extrarenal and expecially on antiarrhythmic effects of triamterene, the latter ones being observed particularly in cases of digitalis intoxication. Considering the digitalis-antagonistic effects, which are also observed in the course of experimental investigations, it was assumed that triamterene, a potassium-saving diuretic, displaces cardiac glycosides from their binding sites in cardiac membranes. The binding of [3H]-g-strophanthin ([3H]-ouabain) and the activity of the (Na+ + K+)-ATPase in the presence of different concentrations of triamterene have been studied with isolated cardiac cell membranes (human; bovine) and human erythrocyte membranes. Inhibition of the binding of the cardiac glycoside and the enzyme activity was only observed for very high concentrations of the active component. These observations are indicative of non-specific effects. Triamterene applied in the presence of different concentrations of strophanthin (10(-9)--5 X 10(-7) M) did not display protective effects on the (Na+ + K+)-ATPase activity. In experiments aimed at chromatographic separations, it could be shown that [3H]-triamterene binds to membrane proteins different from those binding [3H]-g-strophanthin, the latter having been shown to be present in the (Na+ + K+)-ATPase containing fraction. From the results of these experiments it may be concluded that there is no interaction between triamterene and strophanthin on the membrane bound receptor for the cardiac glycoside. [3H]-Triamterene shows concentration dependent binding to cell membranes. This binding is affected to different degrees by Mg++, K+, Na+ and Ca++. The binding sites show low affinity but high binding capacity for triamterene. The significance of this fact remains to be established.

Adenosine Triphosphatases↗
PubMed1975

Quantitative aspects of ouabain binding to human erythrocyte and cardiac membranes.

1. [3H]ouabain binding to human erythrocyte membranes is a time- and temperature-dependent process. The association of ouabain to the membrane-bound receptor follows second-order kinetics, while the dissociation is a monomolecular reaction. An association rate constant of 4-6 x 10(4) M-1 sec-1 and a dissociation rate constant of 1-4 x 10(-4) sec-1 were measured at 37 degrees C. The dissociation constant calculated from these data agrees with that determined from equilibrium binding experiments. There is only one type of ouabain binding sites with high affinity for the drug as reflected by the low dissociation constant of 0-28 x 10(-8) M. 2. The dissociation constants of the ouabain-receptor complexes from human erythrocyte and cardiac membranes are identical. 3. The maximal number of membrane-bound ouabain binding sites was measured from equilibrium binding experiments as 288 +/- 28 per single erythrocyte. Thus one receptor site corresponds to less than 1 mum2 of the membrane, provided the receptors are diffusely distributed on the surface of the membrane. 4. Neither the maximal number of ouabain receptors nor the affinity for the drug changes with the age or sex of the blood donor. 5. A maximal transport capacity for sodium of 5-6 m-equiv/hr.1. is calculated from the number of receptor sites per erythrocyte and from the turn-over number of the (Na+ + K+)-ATPase.

Adenosine Triphosphatases↗
PubMed1975

Cardiac glycoside receptor in potassium depletion.

Ouabain binding capacity of cell membranes is directly related to (Na+ + K+)-ATPase activity. The extent of ouabain inhibition of (Na+ + K+)-ATPase is a measure of ouabain receptor sites occupied. Dissociation constants of the ouabain-receptor complexes are identical in all organs in a single species but vary among different species. K+ decreases the association rate constant of the ouabain receptor interaction without altering the dissociation rate constants. Titration of digoxin-inhibited (Na+ + K+)-ATPase from guinea pig heart with digoxin antibodies shows a reversal of the inhibition at lower antibody concentrations in the presence of K+ than in the absence of K+. It is concluded that digitalis intolerance in acute hypokalemia reflects the increased affinity of the cardiac glycoside receptor under these conditions.

Adenosine Triphosphatases↗