[Water movements in isolated striated muscle subjected to repeated tetanization]

The uptake of cardiac glycosides in relation to their actions in isolated cardiac muscle

1. The uptake of (3)H-digitoxin, (3)H-ouabain and (3)H-dihydro-ouabain by isolated guinea-pig atria has been studied and compared with the inhibition of the sodium pump and with the inotropic effect.2. Analysis of the curve relating the uptake of digitoxin and ouabain at equilibrium to the bath concentration enabled a non-saturable and a saturable binding site to be distinguished.3. The uptake of inactive doses of dihydro-ouabain was only by a non-saturable mechanism.4. The uptake of labelled digitoxin and ouabain was reduced in the presence of another glycoside. The amount of bound glycoside was nearly equivalent to the estimated non-saturable uptake.5. The uptake was reduced at 4 degrees C to the clearance of the non-saturable site.6. ED50 of digitoxin and of ouabain for inhibition of the sodium pump were measured and compared to the ED50 for inotropic effect and to the concentrations producing a half-saturation of the saturable binding site.7. It is concluded that binding to the saturable site may be responsible for the cardiac actions of the glycosides.

The uptake of cardiac glycosides by intestinal smooth muscle of the guinea-pig in relation to digitalis receptors

1. The accumulation and release of (3)H-digitoxin, (3)H-digoxin and (3)H-ouabain by isolated guinea-pig intestinal smooth muscle has been studied and compared with a pharmacological action due to inhibition of the sodium pump.2. The uptake of labelled cardiac glycosides can be described by means of an exponential function. The t of uptake was similar for the three compounds and did not depend on the concentration.3. Analysis of the curve relating the uptake of cardiac glycosides at equilibrium to the bath concentration enabled a non-saturable and a saturable binding site to be distinguished.4. In contrast to the uptake observations, the onset of the pharmacological effect was dependent on the concentration, and furthermore the t((1/2)) for this effect was shorter.5. The release of cardiac glycosides proceeded more slowly than the uptake.6. The uptake of a labelled glycoside was reduced in the presence of another glycoside. The amount of displaceable glycoside was nearly equivalent to the capacity of the saturable binding site.7. The significance of these results is discussed.