PARTICIPATION OF NITRIC-OXIDE SIGNALING SYSTEM IN THE CARDIAC MUSCARINIC CHOLINERGIC EFFECT OF HUMAN CHAGASIC IGG

The possible role of altered humoral immune reponse in the pathogenesi s of the chronic chagasic cardioneuromyopathy was examined by analyzin g the interaction of IgG from T. cruzi infected patients with cardiac muscarinic acetylcholine receptors (mAChR). Human chagasic IgG by acti vating cardiac M-2 mAChR, simulated the agonist actions triggering neg ative inotropic effect, inositol phosphate accumulation,;nitric oxide synthase stimulation and increased production of cycle GMP. Inhibitors of phospholipase C, protein kinase C, calcium/calmodulin, nitric oxid e synthase and guanylate cyclase activities; prevented chagasic IgG ef fects on signaling pathways involved in M-2 mAChR activation, In addit ion, sodium nitroprusside or 8-bromo cyclic GMP, mimicked the chagasic IgG effect associated with cholinergic-mediated cellular transmembran e signals, Moreover, these chagasic IgG immunoprecipitated the mAChRs solubilized from cardiac membranes, By means of SDS-PAGE and immunoblo tting analysis, chagasic sera recognized a band of 70-75 kDa. The majo r protein recognized by chagasic IgG had an Rf coincident with the pea k of [H-3] propylbenzilylcholine mustard with an apparent molecular we ight similar to that of mAChRs, which disappeared in the presence of a tropine, The specificity of this interaction was checked by immunoprec ipitation of rat cardiac mAChR and immunoblotting of pure human M-2 mA ChRs. Chronic interaction of chagasic IgG with myocardial mAChRs, beha ving as a muscarinic agonist, might lead to cell dysfunction or tissue damage, Also, these antibodies could produce desensitization, interna lization or degradation of mAChRs; explaining the progressive blockade of mAChRs in myocardium with parasympathetic denervation, a phenomeno n that has been described in the course of Chagas' cardioneuromyopathy . (C) 1997 Academic Press Limited.