IMMUNOCYTOCHEMICAL LOCALIZATION OF M2 MUSCARINIC RECEPTORS IN RAT VENTRICLES WITH ANTIPEPTIDE ANTIBODIES

We produced antibodies against a synthetic peptide corresponding to am ino acids 168-192 of the second extracellular loop of the M2 human mus carinic receptor in rabbits. In immunoblot, affinity-purified antibodi es specifically recognized a major band of rat ventricular muscarinic receptor protein with a molecular weight of about 80 KD. This recognit ion could be blocked by pre-incubation with peptide. Moreover, with bo th light (LM) and electron microscopic (EM) immunocytochemistry techni ques, muscarinic receptors were detected on sarcolemma and T-tubules o f rat cardiomyocytes. In addition, immunoreactions were localized in m embranes of capillaries. Likewise, these reactivities were abolished b y pre-incubation with peptide. These results suggest that the antibodi es against the second extracellular loop of human M2 muscarinic recept or could specifically recognize rat ventricular muscarinic receptor pr otein and could be a powerful tool to study the fate of this receptor under different pathological or physiological conditions.