Expression of α1-adrenergic receptor subtypes in heart cell culture

Three α1AR subtypes have been cloned so far and are designated as α1a, α1b, and α1d. Organspecific distribution pattern and subtype-specific effects are known but not fully understood. To address a cell-type specific expression pattern in the heart we investigated expression pattern of α1AR subtypes on RNA and proteinlevel in heart tissue, cultured cardiomyocytes and nonmyocytes of the rat. Each α1ARsubtype mRNA was present in neonatal and adult rat heart culture but the relative distribution pattern was significantly different. While the α1aAR subtype is preferentially expressed in adult cardiomyocytes, the α1bAR subtype was preferentially expressed in the nonmyocyte cell fraction. The RTPCR results were confirmed by Westernblotting (α1b) and immunocytochemical studies. Incubation with an α1agonist (phenylephrine) for 72 h led to a significant reduction of the α1bAR in neonatal heart cell culture on both mRNA and protein level. In contrast, incubation with an α1antagonist (prazosin) induced a 1.6 fold upregulation of the α1aAR mRNA without significant effects on radioligand binding and functional assay. The results indicate a distribution pattern of the α1AR subtype which is specific for cell type and ontogeny of the rat heart and may be regulated by adrenergic agents.