Ischemic preconditioning prevents I/R-induced alterations in SR calcium-calmodulin protein kinase II

Although Ca2+/calmodulin- dependent protein kinase II (CaMK II) is known to modulate the function of cardiac sarcoplasmic reticulum (SR) under physiological conditions, the status of SR CaMK II in ischemic preconditioning (IP) of the heart is not known. IP was induced by subjecting the isolated perfused rat hearts to three cycles of brief ischemia-reperfusion (I/R; 5 min ischemia and 5 min reperfusion), whereas the control hearts were perfused for 30 min with oxygenated medium. Sustained I/R in control and IP groups was induced by 30 min of global ischemia followed by 30 min of reperfusion. The left ventricular developed pressure, rate of the left ventricular pressure, as well as SR Ca2+-uptake activity and SR Ca2+-pump ATPase activity were depressed in the control I/R hearts; these changes were prevented upon subjecting the hearts to IP. The beneficial effects of IP on the I/R-induced changes in contractile activity and SR Ca2+ pump were lost upon treating the hearts with KN-93, a specific CaMK II inhibitor. IP also prevented the I/R-induced depression in Ca2+/calmodulin-dependent SR Ca2+-uptake activity and the I/R-induced decrease in the SR CaMK II activity; these effects of IP were blocked by KN-93. The results indicate that IP may prevent the I/R-induced alterations in SR Ca2+ handling abilities by preserving the SR CaMK II activity, and it is suggested that CaMK II may play a role in mediating the beneficial effects of IP on heart function.