L-type Ca2+ channel facilitation mediated by H2O2-induced activation of CaMKII in rat ventricular myocytes

The Ca2+-dependent facilitation (CDF) of L-type Ca2+ channels, a major mechanism for force-frequency relationship of cardiac contraction, is mediated by Ca2+/CaM-dependent kinase II (CaMKII). Recently, CaMKII was shown to be activated by methionine oxidation. We investigated whether oxidation-dependent CaMKII activation is involved in the regulation of L-type Ca2+ currents (ICa,L) by H2O2 and whether Ca2+ is required in this process. Using patch clamp, ICa,L was measured in rat ventricular myocytes. H2O2 induced an increase in ICa,L amplitude and slowed inactivation of ICa,L. This oxidation-dependent facilitation (ODF) of ICa,L was abolished by a CaMKII blocker KN-93, but not by its inactive analog KN-92, indicating that CaMKII is involved in ODF. ODF was not affected by replacement of external Ca2+ with Ba2+ or presence of EGTA in the internal solutions. However, ODF was abolished by adding BAPTA to the internal solution or by depleting sarcoplasmic reticulum (SR) Ca2+ stores using caffeine and thapsigargin. Alkaline phosphatase, β-iminoadenosine 5′-triphosphate (AMP-PNP), an autophosphorylation inhibitor autocamtide-2-related inhibitory peptide (AIP), or a catalytic domain blocker (CaM-KIINtide) did not affect ODF. In conclusion, oxidation-dependent facilitation of L-type Ca2+ channels is mediated by oxidation-dependent CaMKII activation, in which local Ca2+ increases induced by SR Ca2+ release is required.