Spatial heterogeneity of muscarinic type 2 receptors in the atrium

Atrial fibrillation (AF) is the most common arrhythmia in clinical practices. Mediated by muscarinic type 2 receptors (M2Rs), acetylcholine affects electrophysiological activities of atrial myocytes and may contribute to the onset of AF. In order to characterize the distribution of M2Rs in the atrial myocardium, different atrial regions in both the SD rat and human were dissected. Atrial myocytes were isolated with type II collagenase. The M2Rs expression in these atrial tissues and myocytes was detected by immunofluorescent staining and confocal laser scanning biological microscope. The results showed the highest density of M2Rs in atrial myocytes of the left atrial posterior wall. It is concluded that there is a marked spatial heterogeneity in the expression of the M2Rs in the atrium, which might create a substrate that would favor the initiation and maintenance of acetylcholine-induced AF.