Modification of cardiac ionic currents by photosensitizer-generated reactive oxygen

The effects of reactive oxygen species (ROS) generated by light and the photosensitizer Rose Bengal on ionic currents in single frog atrial cells were investigated. The excitatory inward sodium and calcium currents were both suppressed by ROS as was the outward, delayed rectifier potassium current. The inactivation kinetics of the sodium current were slowed markedly whereas the kinetics of calcium current inactivation were much less affected and potassium current activation was not changed. The sodium current-voltage relationship was shifted in the depolarizing direction by ROS whereas the voltage-dependencies of both the calcium and potassium currents were not affected. In addition to suppressing the time- and voltage-dependent sodium, calcium, and potassium currents, ROS enhanced a time-independent current which was outwardly directed at positive membrane potentials. However, the induction of this time-independent current required longer ROS exposure than was required to significantly suppress the other currents. The rapid onset of ROS-induced suppression of calcium and potassium currents followed by a later enhancement of a time-independent current can explain ROS-induced changes in action potential duration. Brief ROS exposure increased action potential duration whereas longer exposure reduced action potential duration.