Mice with genetic inhibition (AC3-I) of the multifunctional
Ca(2+)/calmodulin dependent protein kinase II (
CaMKII) have improved cardiomyocyte survival after
ischemia. Some K(+) currents are up-regulated in AC3-I hearts, but it is unknown if
CaMKII inhibition increases the
ATP sensitive K(+) current (I(KATP)) that underlies ischemic preconditioning (IP) and confers resistance to
ischemia. We hypothesized increased I(KATP) was part of the mechanism for improved ventricular myocyte survival during
ischemia in AC3-I mice. AC3-I hearts were protected against global
ischemia due to enhanced IP compared to wild type (WT) and transgenic control (AC3-C) hearts. IKATP was significantly increased, while the negative regulatory dose-dependence of
ATP was unchanged in AC3-I compared to WT and AC3-C ventricular myocytes, suggesting that
CaMKII inhibition increased the number of functional I(
KATP) channels available for IP. We measured increased sarcolemmal Kir6.2, a pore-forming I(KATP) subunit, but not a change in total Kir6.2 in cell lysates or single channel I(KATP) opening probability from AC3-I compared to WT and AC3-C ventricles, showing
CaMKII inhibition increased sarcolemmal I(
KATP) channel expression. There were no differences in
mRNA for genes encoding I(
KATP) channel subunits in AC3-I, WT and AC3-C ventricles. The I(KATP) opener
pinacidil (100 microM) reduced MI area in WT to match AC3-I hearts, while the I(KATP) antagonist HMR1098 (30 microM) increased MI area to an equivalent level in all groups, indicating that increased I(KATP) and augmented IP are important for reduced ischemic cell death in AC3-I hearts. Our study results show
CaMKII inhibition enhances beneficial effects of IP by increasing I(KATP).