ATO prolonged cardiac action potentials.
(A) Dose-dependent and frequency-dependent prolongation of APD. After action potential was stably stimulated with a frequency of 1 Hz in control condition, ATO (1 μM) was perfused and the effects were recorded. The stimulation frequency was then changed to 0.1 Hz, and then to 2 Hz. The perfusate was then shifted to that containing 10 μM ATO. The changes induced by 3 different stimulation frequencies were recorded. Finally the effect of 25 μM ATO was tested in the same way. Using conventional action potential recording technique, we demonstrated dose-dependent prolongation of APD90 in guinea pig papillary muscle by ATO when the muscle was stimulated with a frequency of 0.1 Hz. The changes in APD90 by faster frequencies (1 and 2 Hz) did not reach statistical significance. *P < .05 versus control; #P < .01 versus control. (B) A typical illustration of action potentials. ATO dose dependently prolonged action potential duration. The stimulation frequency was 0.1 Hz.
