Immunocytochemical localization of muscarinic, adrenergic and AT1 receptors.

By indirect immunofluorescence and post-embedding EM gold technique, the localization of alpha 1-adrenergic, M2-muscarinic and angiotensin II receptor-I (AT1) were determinated. With antipeptide antibodies directed against the second extracellular loops of all three receptors, these receptors were found to be localized at the sarcolemma of adult rat cardiomyocytes and at the surface membranes of cultivated neonatal heart cells. Additionally, M2 receptors were localized along T-tubule membranes of both rat and human adult cardiomyocytes. alpha 1-Adrenergic receptors were found intracellular near the surface of atrial granules (ANF-granules). By using M2 and alpha 1-adrenergic receptor antibodies the strongest fluorescence was found in the right atrium of the rat. Besides the localization in cardiomyocytes, AT1 receptors were also localized in outer plasma membranes and the endoplasmic reticulum of fibroblasts, and the surface of smooth muscle cells of the major arteries and veins. Likewise, the muscarinic M2 receptors were found along the outer membranes of endothelial cells from capillaries and endocardium.