Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a key regulator of myocardial Ca-handling proteins, and is shown to mediate Ca-related pathologies in ischemia/reperfusion, including reperfusion arrhythmias. Marked differences in male/female cardiomyocyte Ca-handling and ischemic vulnerability have been identified. As sex-specificity of CaMKII involvement has not been defined, the goal of this study was to assess CaMKII activation in post-ischemic female/male hearts.

Isolated, Langendorff-perfused (37˚C, non-paced) rat hearts (male/female, n=9) were subjected to 20mins ischemia and 2mins reperfusion (timepoint of peak CaMKII activity in early reperfusion), and compared with non-ischemic aerobic controls. An additional group of hearts was treated with 2mins high Ca (4mM) after 15mins aerobic perfusion and left ventricular function measured using an intraventricular balloon.

Female hearts exhibited lower CaMKII autophosphorylation (autoP-CaMKII; arb. units, male vs female; 0.76±0.10 vs 0.49±0.06, p<0.05) and phospholamban phosphorylation (PLB-Thr17, CaMKII-specific; 0.062±0.010 vs 0.03±0.008, p<0.05) under basal, normoxic conditions. A similar trend in ryanodine receptor phosphorylation (RyR-Ser2814, CaMKII-specific) was observed. However, the CaMKII response at 2mins reperfusion was augmented in female hearts, with autoP-CaMKII, PLB-Thr17 , and RyR-Ser2814 all significantly increased vs males.

In hearts perfused with high Ca, autoP-CaMKII was also increased in females vs males (0.96±0.06 vs 1.22±0.08, p<0.05) and the extent of increase in PLB-Thr17 (fold change over basal; 1.5±0.2 vs 2.8±0.5, p<0.05) was greater. This increased CaMKII response to high Ca in female hearts was associated with an enhanced capacity to maintain stable end diastolic pressure, whereas this parameter was found to be elevated in males.

These data indicate that upregulation of CaMKII activity is accentuated in females, even though arrhythmias are reduced in early reperfusion. These findings may suggest a different regulatory relationship between CaMKII stimulation and arrhythmogenesis in female and male hearts which is of therapeutic relevance.