Abstract 360: Ca/Calmodulin Kinase II (CaMKII) Overexpression Increases Effects of Reactive Oxygen Species to Enhance Late INa and Raise [Na 3]i and [Ca 2+]i
In heart failure (HF), CaMKII expression and reactive oxygen species (ROS) production are increased. We have shown that CaMKII increases late INa and [Na+]i. ROS enhance late INa leading to Na and Ca overload. We therefore used adenoviral gene transfer (CaMKII, MOI 100, 24 h, vs. LacZ) to overexpress CaMKIIδc in rabbit myocytes and measured [Ca2+ ]i with Indo-1 (10 μmol/L) and [Na+]i with SBFI (10 μmol/L, 37°C) Late INa was measured using whole cell patch clamp, integrated from 50–500 ms post-stimulus, and expressed as % of peak INa. ROS (200 μM H2O2, 20 min) increased late INa to 1.29±0.27 (N =6) and 2.33±0.6% (N = 8) of peak INa in control and CaMKIIδc-overexpressing myocytes, respectively (P<0.05). Upon ROS exposure, [Na+]i increased with time in myocytes stimulated at 0.5 Hz. The ROS-induced increase of [Na+]i was significantly greater in CaMKII-overexpressing (N=26) vs. LacZ (N=28) myocytes, P<0.05 (Fig. A⇓) but was reduced with CaMKII inhibition (1 μmol/L KN93, N=9, P<0.05) and by the late INa inhibitor ranolazine (RAN, 10 μmol/L, N=9, P<0.05). ROS increased diastolic [Ca2+]i more rapidly in CaMKII-overexpressing (N=11) than in control (N=10) myocytes (P<0.05, Fig. B⇓), but more slowly when either KN93 or ranolazine was present (N=9 and 8, P<0.05). In saponin-permeabilized myocytes, exposure to ROS increased the amount of phospho-CaMKII (at Thr287, Western blot) relative to CaMKII. In conclusion, ROS increase late INa, [Na+ ]i and [Ca2+ ]i more rapidly in CaMKIIδc-overexpressing myocytes than in control myocytes. These increases are greatly attenuated by KN93 and RAN, suggesting that ROS require CaMKIIδc to enhance late INa, and late INa then leads to elevations of [Na+]i and [Ca2+]i.