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

Abstract

We hypothesized that the cardioprotective effect of angiotensin II type 2 receptor (AT2R) 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 AT2R protein and mRNA as well as an increase in inositol 1,4,5-trisphosphate type 2 receptor (IP3R) and protein kinase Cε (PKCε) proteins. We assessed AT2R, angiotensin II type 1 receptor (AT1R), IP3R, and PKCε protein expression (Western blots) and AT2R 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 μmol/L), IR, and IR+PD. Compared with no IR and no IR+PD, IR decreased (P<0.05) functional recovery and AT2R mRNA and protein, as well as AT1R mRNA (not protein) and IP3R and PKCε proteins. Compared with IR, PD+IR improved LV functional recovery (P<0.05) and markedly increased AT2R mRNA and protein (P<0.001). However, PD did not change AT1R mRNA or protein. More importantly, PD+IR markedly increased IP3R and PKCε proteins. The downregulation of AT2R mRNA and protein with IR and their upregulation with PD indicate that the effects of PD are AT2R 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 AT2R blockade and is associated with enhanced downstream IP3R and pKCε signaling.