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 μM) 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.