Regulation of cardiac ATP-sensitive potassium channel surface expression by calcium/calmodulin-dependent protein kinase II

Background: Surface expression of cardiac ATP-sensitive potassium (KATP) channels impacts cellular energy homeostasis. Results: Activation of calcium/calmodulin-dependent protein kinase II (CaMKII) results in KATP channel internalization, requiring specific motifs on the Kir6.2 channel subunit. Conclusion: CaMKII phosphorylation of Kir6.2 promotes endocytosis of cardiac KATP channels. Significance: This mechanism reveals new targets to improve cardiac energy efficiency and stress resistance. Cardiac ATP-sensitive potassium (KATP) channels are key sensors and effectors of the metabolic status of cardiomyocytes. Alteration in their expression impacts their effectiveness in maintaining cellular energy homeostasis and resistance to injury. We sought to determine how activation of calcium/calmodulin-dependent protein kinase II (CaMKII), a central regulator of calcium signaling, translates into reduced membrane expression and current capacity of cardiac KATP channels. We used real-time monitoring of KATP channel current density, immunohistochemistry, and biotinylation studies in isolated hearts and cardiomyocytes from wild-type and transgenic mice as well as HEK cells expressing wild-type and mutant KATP channel subunits to track the dynamics of KATP channel surface expression. Results showed that activation of CaMKII triggered dynamin-dependent internalization of KATP channels. This process required phosphorylation of threonine at 180 and 224 and an intact 330YSKF333 endocytosis motif of the KATP channel Kir6.2 pore-forming subunit. A molecular model of theμ2 subunit of the endocytosis adaptor protein, AP2, complexed with Kir6.2 predicted thatμ2 docks by interaction with 330YSKF333 and Thr-180 on one and Thr-224 on the adjacent Kir6.2 subunit. Phosphorylation of Thr-180 and Thr-224 would favor interactions with the corresponding arginine-and lysine-rich loops on μ2. We concluded that calcium-dependent activation of CaMKII results in phosphorylation of Kir6.2, which promotes endocytosis of cardiac KATP channel subunits. This mechanism couples the surface expression of cardiac KATP channels with calcium signaling and reveals new targets to improve cardiac energy efficiency and stress resistance.