Enhanced Expression of Angiotensin II Type 2 Receptor, Inositol 1,4,5-Trisphosphate Receptor, and Protein Kinase Cε During Cardioprotection Induced by Angiotensin II Type 2 Receptor Blockade

We hypothesized that the cardioprotective effect of angiotensin II type 2 receptor (AT(2)R) blockade with PD 123,319 (PD) on the recovery of left ventricular (LV) mechanical function after ischemia/reperfusion (IR) in the isolated working rat heart is associated with the enhanced expression of AT(2)R protein and mRNA as well as an increase in inositol 1,4,5-trisphosphate type 2 receptor (IP(3)R) and protein kinase Cepsilon (PKCepsilon) proteins. We assessed AT(2)R, angiotensin II type 1 receptor (AT(1)R), IP(3)R, and PKCepsilon protein expression (Western blots) and AT(2)R mRNA levels (Northern blots) in myocardium from isolated working rat hearts that were subjected to global ischemia (30 minutes) followed by reperfusion (30 minutes). Groups of adult rat hearts (n=6) were exposed to no IR, no IR+PD (0.3 micromol/L), IR, and IR+PD. Compared with no IR and no IR+PD, IR decreased (P<0.05) functional recovery and AT(2)R mRNA and protein, as well as AT(1)R mRNA (not protein) and IP(3)R and PKCepsilon proteins. Compared with IR, PD+IR improved LV functional recovery (P<0.05) and markedly increased AT(2)R mRNA and protein (P<0.001). However, PD did not change AT(1)R mRNA or protein. More importantly, PD+IR markedly increased IP(3)R and PKCepsilon proteins. The downregulation of AT(2)R mRNA and protein with IR and their upregulation with PD indicate that the effects of PD are AT(2)R specific. The overall results suggest that the cardioprotective effect of acute PD treatment on LV functional recovery after IR in the isolated working rat heart is specifically due to AT(2)R blockade and is associated with enhanced downstream IP(3)R and PKCepsilon signaling.