IMMUNOLOCALIZATION OF SUBTYPE-2 ANGIOTENSIN-II (AT(2)) RECEPTOR PROTEIN IN RAT-HEART

Angiotensin II exerts its effects on cardiovascular function and water and sodium homeostasis by interacting with plasma membrane receptors on target organs. The existence of subtype 2 angiotensin II (AT(2)) re ceptors in the rat heart has been demonstrated by ligand binding and r everse transcription-polymerase chain reaction. In the present study, the expression and localization of AT(2) receptor protein in the rat h eart was investigated using an antipeptide polyclonal antibody against the native rat AT(2) receptor by light microscopic immunocytochemistr y and Western blot analysis. In frozen tissue sections, positive immun ostaining was observed in the myocardium and coronary vessels througho ut the ventricle and atrium of neonatal and young rat hearts. Coronary vessels of the neonatal heart were more intensely stained compared wi th the surrounding myocardium. Positive immunoreactivity in the corona ry vessels of young rats was localized to vascular endothelium but not in the smooth muscle cells. Preadsorption controls were all negative. Western blot analysis showed that the AT(2) receptor protein (approxi mate to 44 kDa) was detectable from the AT(2) receptor-transfected COS -7 cells and neonatal rat cardiac myocytes but not from fibroblasts or young rat aortic smooth muscle cells. The neonatal rat heart expresse d significantly more AT(2) receptors than young rat heart. These data provide the first direct evidence for the expression and localization of AT(2) receptor protein in the rat heart.