M2 and M3-muscarinic acetylcholine receptors remodelling in patients with a dilated atrium.

BACKGROUND

Studies have shown that autonomic tone plays an important role in the pathogenesis of atrial fibrillation (AF) and remodelling of I(K, ACh) in chronic AF serves as a compensatory mechanism for the AF. The relation between atrial size and AF has been established. We investigated the remodelling of muscarinic receptors in patients with dilated atrium and assessed the relationship between the muscarinic receptor remodelling and the dilated atrium.

METHODS

A small piece of the tip of the right atrial appendage was obtained from 19 patients in sinus rhythm (SR), 28 patients with mitral stenosis and 10 patients with chronic AF (AF > 6 months). Western-blot was used to determine the expression of M2 and M3 receptors.

RESULTS

Patients with mitral stenosis and chronic AF had a larger left atrial diameter than patients in SR. The densities of the M2 receptor in patients with mitral stenosis (with AF and with SR) and chronic AF were lower than that in patients with SR (0.54 +/- 0.08 vs. 0.29 +/- 0.06, 0.26 +/- 0.05 and 0.28 +/- 0.06, P < 0.05). However, the densities of the M3 receptor in patients with mitral stenosis and chronic AF were higher than that in patients with SR (0.07 +/- 0.01 vs. 0.18 +/- 0.02, 0.17 +/- 0.01 and 0.15 +/- 0.01, P< 0.05). Furthermore, there was no significant difference in M2 and M3 receptors between AF and SR in patients with mitral stenosis.

CONCLUSION

Remodelling of M2 and M3 receptors is not associated with AF, but with the dilated left atrium.