LOCALIZATION OF ALPHA(1)-ADRENOCEPTORS IN RAT AND HUMAN HEARTS BY IMMUNOCYTOCHEMISTRY

The localization of the alpha(1) adrenoceptors (alpha(1)-AR) in the he art tissues from rat and human and in the cultured heart cells from ne onatal rats was studied by indirect immunofluorescence and postembeddi ng electronmicroscopical immune-gold technique. With antipeptide antib odies directed against the second extracellular loop of the human alph a(1)-AR (AS sequence 192-218), this receptor was found to be localized along the sarcolemma in both human and rat hearts. Similar localizati on sites were detected in cultivated rat neonatal cardiomyocytes. Besi de the localization in cardiomyocytes, alpha(1)-AR were identified in endothelial cells of capillaries and smooth muscle cells of coronary v essels, in neuronal endings, in mast cells of cultivated heart cells b ut not, or in less amount in fibroblasts. Interestingly, in the right atrium of rat heart the localization of alpha(1)-AR was found to be ne ar or on atrial natriuretic factor (ANF) granules, providing the basis for the a-adrenergic influence on ANF release. The immunocytochemical studies further confirm and complete the findings known by using auto radiographic binding studies with specific ligands.