“ Menadione (30 μM) significantly increased the action potential duration at 90% repolarization (APD90) in Purkinje fibers and ventricular muscles from 18-day old rats; and it decreased the APD in ventricular muscles from 49-day old rats.”
“These results indicate that menadione can produce regionally differential effects on cardiac APD , which may be due to differences in the SOD activity, depending on the region and age of the cardiac tissue.”