Cloning and expression of adrenergic and muscarinic cholinergic receptor genes

Anti-M2 muscarinic receptor antibodies inhibit beta-adrenoceptor-mediated inotropic response in rat myocardium

The modulation of the inotropic effect by affinity-purified antibodies against a synthetic peptide corresponding to the second extracellular loop of the human muscarinic M2 receptors was studied in adult rat ventricular myocardium. These anti-muscarinic M2 receptor antibodies shifted the dose-response relationship of the beta-adrenoceptor agonist isoproterenol to higher concentrations whereas preimmune rabbit immunoglobulin G (IgG) or antibodies against the N-terminus of the beta 1-adrenoceptor had no effect. This effect of anti-muscarinic M2 receptor antibodies was fully blocked after preincubation with the antigenic peptide. No significant change of maximal inotropic response to isoproterenol was observed in the presence of anti-muscarinic M2 receptor antibodies. The anti-muscarinic M2 receptor antibodies did apparently not hamper the access of the muscarinic receptor agonist carbachol. The muscarinic receptor antagonist atropine attenuated the effect of the anti-muscarinic M2 receptor antibodies. The present study demonstrates for the first time in intact adult ventricular myocardium a specific stimulatory muscarinic activity of antibodies raised against a part of the muscarinic M2 receptor protein.

Anti-M2 muscarinic receptor autoantibodies and idiopathic dilated cardiomyopathy

Idiopathic dilated cardiomyopathy is an often fatal cause of heart failure and has been intensively studied over the last 50 years. One of the main mechanisms for this disease is likely to be autoimmunity-mediated myocardial damage. So far, a variety of autoantibodies have been detected against a number of putative cardiac autoantigens in the sera of patients with dilated cardiomyopathy and have thus received increased attention. This article will attempt to focus on clinical and experimental studies of autoimmunity induced by the M2 muscarinic receptor as a putative autoantigen and their implications in idiopathic dilated cardiomyopathy.

Localization of a functional autoimmune epitope on the muscarinic acetylcholine receptor-2 in patients with idiopathic dilated cardiomyopathy

A peptide corresponding to the sequence 169-193 of the second extracellular loop of the human muscarinic acetylcholine receptor-2 was used as an antigen to screen sera from patients with idiopathic dilated cardiomyopathy (DCM, n = 36) and healthy blood donors (HBD, n = 40). The sera from 14 patients with DCM (38.8%) and 3 HBD (7.5%) recognized the muscarinic receptor peptide at dilutions varying from 1:20 to 1:160 in ELISA. A highly significant correlation (P = 0.006) was found between the presence of antimuscarinic receptor-2 autoantibodies and anti-beta-adrenoceptor-1 autoantibodies in the patients' sera. Affinity-purified autoantibodies from positive sera of patients with DCM recognized on the electrotransferred protein of rat ventricular membrane a major band of about 80 kD. Incubation of autoantibodies with membrane resulted not only in a decrease in the maximal binding sites (Bmax) but also in an increase in Kd of radioligand binding in a concentration-dependent manner. This suggests a mixed-type of inhibition. Moreover, preincubation with atropine abolished the inhibitory effect of autoantibodies on the receptor binding whereas carbachol appeared to have no effect on the activity of the autoantibodies. These data define a subgroup of patients with idiopathic DCM who have in their sera functionally active autoantibodies against muscarinic receptor-2.