Mechanisms underlying the modulation of L-type Ca2+ channel by hydrogen peroxide in guinea pig ventricular myocytes

Although Cav1.2 Ca2+ channels are modulated by reactive oxygen species (ROS), the underlying mechanisms are not fully understood. In this study, we investigated effects of hydrogen peroxide (H2O2) on the Ca2+ channel using a patch-clamp technique in guinea pig ventricular myocytes. Externally applied H2O2 (1 mM) increased Ca2+ channel activity in the cell-attached mode. A specific inhibitor of Ca2+/calmodulin-dependent protein kinase II (CaMKII) KN-93 (10 mu M) partially attenuated the H2O2-mediated facilitation of the channel, suggesting both CaMKII-dependent and -independent pathways. However, in the inside-out mode, 1 mM H2O2 increased channel activity in a KN-93-resistant manner. Since H2O2-pretreated calmodulin did not reproduce the H2O2 effect, the target of H2O2 was presumably assigned to the Ca2+ channel itself. A thiol-specific oxidizing agent mimicked and occluded the H2O2 effect. These results suggest that H2O2 facilitates the Ca2+ channel through oxidation of cysteine residue(s) in the channel as well as the CaMKII-dependent pathway.