RyR2 Modulates a Ca(2+)-Activated K(+) Current in Mouse Cardiac Myocytes

In cardiomyocytes, Ca(2+) entry through voltage-dependent Ca(2+) channels (VDCCs) binds to and activates RyR2 channels, resulting in subsequent Ca(2+) release from the sarcoplasmic reticulum (SR) and cardiac contraction. Previous research has documented the molecular coupling of small-conductance Ca(2+)-activated K(+) channels (SK channels) to VDCCs in mouse cardiac muscle. Little is known regarding the role of RyRs-sensitive Ca(2+) release in the SK channels in cardiac muscle. In this study, using whole-cell patch clamp techniques, we observed that a Ca(2+)-activated K+ current (I(K,Ca)) recorded from isolated adult C57B/L mouse atrial myocytes was significantly decreased by ryanodine, an inhibitor of ryanodine receptor type 2 (RyR2), or by the co-application of ryanodine and thapsigargin, an inhibitor of the sarcoplasmic reticulum calcium ATPase (SERCA) (p<0.05, p<0.01, respectively). The activation of RyR2 by caffeine increased the I(K,Ca) in the cardiac cells (p<0.05, p<0.01, respectively). We further analyzed the effect of RyR2 knockdown on I(K,Ca) and Ca(2+) in isolated adult mouse cardiomyocytes using a whole-cell patch clamp technique and confocal imaging. RyR2 knockdown in mouse atrial cells transduced with lentivirus-mediated small hairpin interference RNA (shRNA) exhibited a significant decrease in I(K,Ca) (p<0.05) and [Ca(2+)]i fluorescence intensity (p<0.01). An immunoprecipitated complex of SK2 and RyR2 was identified in native cardiac tissue by co-immunoprecipitation assays. Our findings indicate that RyR2-mediated Ca(2+) release is responsible for the activation and modulation of SK channels in cardiac myocytes.