[Influence of roentgen rays on electrolyte changes and metabolism of the myocardium. VII. Radiation-induced inhibition of the sodium- and potassium--activated microscomal-trasport ATPase].

The behavior of a Mg2+-dependent microsomal ATPase, which may be activated by Na+ and K+, was investigated in the myocardium of Guinea pigs after local irradiation. The part which can be activated by Na+ and K+ (transport-ATPase) is already slightly inhibited thirty minutes after a dose of 250 R; the inhibition rate with 1500 R amounts to about 60%, the maximal inhibition effect with a dose of 3000 R was about 70%. Four hours after a local irradiation with 1500 R, a restitution of the inhibition effect occurs with overshoot reaction; 15 and 24 hours following irradiation, a significant inhibition of the transport-ATPase activity can again be verified. The k-strophanthidine and digitoxin are inhibiting within the concentration ranges analyzed (2 X 10(-5), 2.5 X 10(-7), 5 X 10(-7) M) the activity of the transport-ATPase. The above-mentioned radiation-induced inhibition effect upon the ATPase activated by Na+ and K+ is additively increased by adding k-strophanthidine (2 X 10(-5) M) and digitoxin (2.5 X 10(-7) M).