Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) plays an important role 
mediating apoptosis/necrosis during ischemia-reperfusion (IR). We explored the 
mechanisms of this deleterious effect. Langendorff perfused rat and transgenic 
mice hearts with CaMKII inhibition targeted to sarcoplasmic reticulum (SR-AIP) 
were subjected to global IR. The onset of reperfusion increased the 
phosphorylation of Thr(17) site of phospholamban, without changes in total 
protein, consistent with an increase in CaMKII activity. Instead, there was a 
proportional decrease in the phosphorylation of Ser2815 site of ryanodine 
receptors (RyR2) and the amount of RyR2 at the onset of reperfusion, i.e. the 
ratio Ser2815/RyR2 did not change. Inhibition of the reverse 
Na(+)/Ca(2+)exchanger (NCX) mode (KBR7943) diminished phospholamban 
phosphorylation, reduced apoptosis/necrosis and enhanced mechanical recovery. 
CaMKII-inhibition (KN-93), significantly decreased phospholamban 
phosphorylation, infarct area, lactate dehydrogenase release (LDH) (necrosis), 
TUNEL positive nuclei, caspase-3 activity, Bax/Bcl-2 ratio and Ca(2+)-induced 
mitochondrial swelling (apoptosis), and increased contractile recovery when 
compared with non-treated IR hearts or IR hearts pretreated with the inactive 
analog, KN-92. Blocking SR Ca(2+) loading and release (thapsigargin/dantrolene), 
mitochondrial Ca(2+) uniporter (ruthenium red/RU360), or mitochondrial 
permeability transition pore (cyclosporine A), significantly decreased infarct 
size, LDH release and apoptosis. SR-AIP hearts failed to show an increase in the 
phosphorylation of Thr(17) of phospholamban at the onset of reflow and exhibited 
a significant decrease in infarct size, apoptosis and necrosis respect to 
controls. The results reveal an apoptotic-necrotic pathway mediated by 
CaMKII-dependent phosphorylations at the SR, which involves the reverse NCX mode 
and the mitochondria as trigger and end effectors, respectively, of the cascade.