The multifunctional Ca 2ϩ /calmodulin-dependent protein kinase II ␦ C (CaMKII␦ C ) is found in the macromolecular complex of type 2 ryanodine receptor (RyR2) Ca 2ϩ release channels in the heart. However, the functional role of CaMKII-dependent phosphorylation of RyR2 is highly controversial. To address this issue, we expressed wild-type, constitutively active, or dominant-negative CaMKII␦ C via adenoviral gene transfer in cultured adult rat ventricular myocytes. CaMKII-mediated phosphorylation

more »

... f RyR2 was reduced, enhanced, or unaltered by dominant-negative, constitutively active, or wild-type CaMKII␦ C expression, whereas phosphorylation of phospholamban at Thr17, an endogenous indicator of CaMKII activity, was at 73%, 161%, or 115% of the control group expressing ␤-galactosidase (␤-gal), respectively. In parallel with the phospholamban phosphorylation, the decay kinetics of global Ca 2ϩ transients was slowed, accelerated, or unchanged, whereas spontaneous Ca 2ϩ spark activity was hyperactive, depressed, or unchanged in dominant-negative, constitutively active, or wild-type CaMKII␦ C groups, respectively. When challenged by high extracellular Ca 2ϩ , both wild-type and constitutively active CaMKII␦ C protected the cells from store overload-induced Ca 2ϩ release, manifested by a Ϸ60% suppression of Ca 2ϩ waves (at 2 to 20 mmol/L extracellular Ca 2ϩ ) in spite of an elevated sarcoplasmic reticulum Ca 2ϩ content, whereas dominant-negative CaMKII␦ C promoted Ca 2ϩ wave production (at 20 mmol/L Ca 2ϩ ) with significantly depleted sarcoplasmic reticulum Ca 2ϩ . Taken together, our data support the notion that CaMKII␦ C negatively regulates RyR2 activity and spontaneous sarcoplasmic reticulum Ca 2ϩ release, thereby affording a negative feedback that stabilizes local and global Ca 2ϩ -induced Ca 2ϩ release in the heart. (Circ Res. 2007;100:399-407.) Key Words: Ca 2ϩ /calmodulin-dependent protein kinase II Ⅲ Ryanodine receptor Ⅲ Ca 2ϩ sparks Ⅲ Ca 2ϩ waves Ⅲ Ca 2ϩ -induced Ca 2ϩ release