M3 muscarinic acetylcholine receptor is associated with beta-catenin in ventricular myocytes during myocardial infarction in the rat.

1. The present study was designed to investigate whether the M(3) muscarinic acetylcholine receptors (mAChR) is associated with beta-catenin in the ventricular myocardium during ischaemic myocardial injury and to determine the possible mechanism/s involved. 2. Rat hearts were subjected to coronary artery ligation for 1 and 6 h or 1 month to establish a myocardial ischaemia (MI) model. In the acute MI model, 16 rats were randomized into four groups: (i) control; (ii) ischaemia (rats were subjected to 20 min coronary occlusion); (iii) choline (10 mg/kg, i.v., choline chloride, an M(3) receptor agonist, was administered 15 min before occlusion); and (iv) 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP; 0.12 mg/kg 4-DAMP, an M(3) receptor antagonist, was administered 20 min before occlusion, followed 5 min later by 10 mg/kg, i.v., choline chloride). Immunochemistry, western blot analysis and immunoprecipitation were used to determine the expression and localization of beta-catenin and the M(3) mAChR. 3. Myocardial ischaemia caused a time-dependent increase in the expression of beta-catenin. Moreover, a physical association was found between beta-catenin and the M(3) mAChR in intercalated discs. This association was enhanced by prolonged ischaemia. Administration of choline before ischaemia not only increased beta-catenin expression, but also strengthened the association between beta-catenin and the M(3) mAChR. However, blockade of M(3) mAChR by 4-DAMP completely inhibited the effect of choline on the expression of beta-catenin. In addition, MI increased phosphorylation of the M(3) mAChR. 4. The results indicate that increased beta-catenin activity is associated with M(3) mAChR during MI. This association is likely to play a role in heart signal transduction during ischaemia between neighbouring ventricular myocardiocum.