Uptake and liberation of [3H]16-acetyl-gitoxin in the isolated guinea pig atrium.

In isolated, spontaneously beating guinea-pig atria the uptake, liberation and inotropic effect of [3H]16-acetyl-gitoxin were studied. At a concentration of 53.5 nmol/l 16-acetyl-gitoxin caused an increase in contractile force of 21% within 45 min. Within 60 min, 190.7 pmol per g tissue were taken up. The tissue-to-medium radioactivity ratio (T/M ratio) was 4.7. In the wash-out experiments, 40% of the accumulated radioactivity was liberated into the medium within 30 min, while the glycoside-dependent increment of inotropy ceased to continue. The kinetic properties of 16-acetyl-gitoxin were found to resemble more closely those of digitoxin than those of ouabain.