Expression of [alpha]1-adrenergic receptor subtypes in heart cell culture

Three α^sub 1^AR subtypes have been cloned so far and are designated as α^sub 1a^, α^sub 1b^, and α^sub 1d^. 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 α^sub 1^AR subtypes on RNA and proteinlevel in heart tissue, cultured cardiomyocytes and nonmyocytes of the rat. Each α^sub 1^ARsubtype mRNA was present in neonatal and adult rat heart culture but the relative distribution pattern was significantly different. While the α^sub 1a^AR subtype is preferentially expressed in adult cardiomyocytes, the α^sub 1b^AR subtype was preferentially expressed in the nonmyocyte cell fraction. The RTPCR results were confirmed by Westernblotting (α^sub 1b^) and immunocytochemical studies. Incubation with an α^sub 1^agonist (phenylephrine) for 72 h led to a significant reduction of the α^sub 1b^AR in neonatal heart cell culture on both mRNA and protein level. In contrast, incubation with an α^sub 1^antagonist (prazosin) induced a 1.6 fold upregulation of the α^sub 1a^AR mRNA without significant effects on radioligand binding and functional assay. The results indicate a distribution pattern of the α^sub 1^AR subtype which is specific for cell type and ontogeny of the rat heart and may be regulated by adrenergic agents.[PUBLICATION ABSTRACT]