Reactive oxygen species (ROS) have been implicated in the pathophysiology of myocardial hypertrophy and failure. Although mechanism(s) of ROS-induced cardiac damage remains unclear, there is increasing evidence for ROS-mediated increase of intracellular free Ca2+ concentration. To investigate the growth-related molecular targets of reactive oxygen, we examined redox sensitivity of L-type Ca2+ currents (ICa) in rat ventricular myocytes. ICa was assessed by using the perforated patch clamp technique. Addition of H2O2 over a broad concentration range (250-1000 µM) increased ICa in a time-and dose-dependent manner. This effect was completely blocked when cells were pretreated by dithiothreitol (5 mM). A 15-min loading of ventricular myocytes with the Ca2+ chelator, BAPTA-AM (10 µM) significantly reduced H2O2-induced increase of ICa by 67.6짹10.9 % (n=3). The calmodulin antagonists, calmidazolium (1 µM) caused similar reductions in H2O2-induced increase of ICa. BAPTA and calmidazolium did not affect the control ICa. H2O2 caused a marked increase in both striated and nonstriated actin fibers and this actin rearrangement was prevented by the calmodulin inhibitor. Further, cytoskeletal disruption with cytochalasin D (10 µM) decreased the H2O2-induced increase of ICa by 57.5짹4.2 % (n=3). These results suggest that cytoskeletal rearrangements are responsible, at least in part, for the modulation of L-type Ca2+ channel by H2O2 and that Ca2+/calmodulin pathway may be involved in this process.