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 (M(2)Rs), acetylcholine affects electrophysiological activities of atrial myocytes and may contribute to the onset of AF. In order to characterize the distribution of M(2)Rs 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 M(2)Rs 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 M(2)Rs in atrial myocytes of the left atrial posterior wall. It is concluded that there is a marked spatial heterogeneity in the expression of the M(2)Rs in the atrium, which might create a substrate that would favor the initiation and maintenance of acetylcholine-induced AF.