Differential activation of nitric oxide synthase through muscarinic acetylcholine receptors in rat salivary glands.

Muscarinic receptors play an important role in secretory and vasodilator responses in rat salivary glands. Nitric oxide synthase (NOS) appears to be one of the multiple effectors coupled to muscarinic receptors in both submandibular and sublingual glands although some differences have been found depending on the gland studied. First, submandibular glands had a lower basal activity of nitric oxide synthase than sublingual glands and the concentration-response curve for carbachol was bell-shaped in the former but not in sublingual glands. Second, cGMP levels displayed a similar profile to that observed for NOS activity in both glands. Third, protein kinase C also coupled to muscarinic receptor activation in the glands might have a regulatory effect on nitric oxide production since its activity was higher in basal conditions in submandibular than sublingual glands and it also increased in the presence of the agonist at a concentration that inhibited NOS activity in submandibular glands. The effects appear to be partly related to the expression of a minor population of M(1) receptors in submandibular glands absent in sublingual as determined in binding and signaling experiments with the muscarinic receptor antagonist pirenzepine.

Sjögren autoantibodies modify neonatal cardiac function via M1 muscarinic acetylcholine receptor activation.

Isolated congenital heart block may be associated with primary Sjögren syndrome. In this work we describe circulating antibodies in the sera of primary Sjögren syndrome patients that are able to interact with neonatal myocardium by activating muscarinic acetylcholine receptors of M1 subtype. We report on the presence of autoantibodies against the second extracellular loop of human M1 muscarinic acetylcholine receptors in primary Sjögren syndrome mothers whose children have congenital heart block using a synthetic peptide in indirect immunofluorescence technique. Autoantibodies from primary Sjögren syndrome patients gave positive image on neonatal atria but not on adult atria slices. The synthetic M1 peptide selectively abrogated indirect immunofluorescence recognition. The primary Sjögren syndrome-immunoglobulin G also displayed an 'agonist like' activity modifying the intracellular events associated with muscarinic acetylcholine receptor activation. The mechanism appears to occur secondarily to stimulation of phosphoinositides turnover via phospholipase C activation. This, in turn, triggers cascade reactions involving calcium/calmodulin and leads to activation of nitric oxide synthase and soluble guanylate cyclase. All of these effects were selectively blunted by pirenzepine and neutralized by M1 synthetic peptide. These biological effects were not obtained using adult instead of neonatal rat atria and neither occurred with the sera of normal healthy women of childbearing age. It could be concluded that antibodies against neonatal M1 muscarinic acetylcholine receptor may be another serum factor to be considered in the pathophysiology of the development of congenital heart block associated with primary Sjögren syndrome mothers.

Nitric oxide synthase in experimental autoimmune myocarditis dysfunction.

This study reports the expression of inducible nitric oxide synthase (NOS) in heart from autoimmune myocarditis mice associated with an alteration in their contractile behavior. By mean of the production of [U-14C]citrulline from [U-14C]arginine and immunoblot assay, the expression of iNOS was demonstrated in autoimmune atria that was normally absent. The iNOS activity decreased with administration of dexamethasone and in mice treated with monoclonal anti-interferon-gamma antibody (anti-IFN-gamma mAb). The inhibitors of protein kinase C activity (staurosporine) but not calcium/calmodulin (trifluoperazine) attenuated the iNOS activity. Moreover, autoimmune atria presented contractile alterations (lower values of dF/dt than control). The in vivo treatment with inhibitors of NOS activity or anti-IFN-gamma mAb or dexamethasone improved the contractile activity of autoimmune atria with no change in the contractility of normal atria. The results suggest that the infiltrative cells in myocarditis heart have a potential role in cardiac dysfunction by production of IFN-gamma and subsequent expression of iNOS, that in turn alter the contractile behavior of the heart. The data indicate that cytokines induced activation of L-arginine nitric oxide pathway in myocarditis atria leading to contractile dysfunction.

Participation of nitric oxide signaling system in the cardiac muscarinic cholinergic effect of human chagasic IgG.

The possible role of altered humoral immune response in the pathogenesis of the chronic chagasic cardioneuromyopathy was examined by analyzing the interaction of IgG from T. cruzi infected patients with cardiac muscarinic acetylcholine receptors (mAChR). Human chagasic IgG by activating cardiac M2 mAChR, simulated the agonist actions triggering negative inotropic effect, inositol phosphate accumulation, nitric oxide synthase stimulation and increased production of cyclic GMP. Inhibitors of phospholipase C, protein kinase C, calcium/calmodulin, nitric oxide synthase and guanylate cyclase activities; prevented chagasic IgG effects on signaling pathways involved in M2 mAChR activation. In addition, sodium nitroprusside or 8-bromo cyclic GMP, mimicked the chagasic IgG effect associated with cholinergic-mediated cellular transmembrane signals. Moreover, these chagasic IgG immunoprecipitated the mAChRs solubilized from cardiac membranes. By means of SDS-PAGE and immunoblotting analysis, chagasic sera recognized a band of 70-75 kDa. The major protein recognized by chagasic IgG had an Rf coincident with the peak of [3H] propylbenzilylcholine mustard with an apparent molecular weight similar to that of mAChRs, which disappeared in the presence of atropine. The specificity of this interaction was checked by immunoprecipitation of rat cardiac mAChR and immunoblotting of pure human M2 mAChRs. Chronic interaction of chagasic IgG with myocardial mAChRs, behaving as a muscarinic agonist, might lead to cell dysfunction or tissue damage. Also, these antibodies could produce desensitization, internalization or degradation of mAChRs; explaining the progressive blockade of mAChRs in myocardium with parasympathetic denervation, a phenomenon that has been described in the course of Chagas' cardioneuromyopathy.

Desensitization and sequestration of human m2 muscarinic acetylcholine receptors by autoantibodies from patients with Chagas' disease.

Chronic Chagas' disease is associated with pathologic changes of the cardiovascular, digestive, and autonomic nervous system, culminating in autonomic denervation and congestive heart failure. Previously, circulating autoantibodies that activate signaling by cardiac muscarinic acetylcholine receptors (mAChRs) have been described. However, it remains unclear whether the chagasic IgGs directly interact with the m2 mAChRs (predominant cardiac subtype), and, if so, whether chronic exposure of the mAChRs to such activating IgGs would result in receptor desensitization. Here we performed studies with purified and reconstituted hm2 mAChRs and demonstrate that IgGs from chagasic serum immunoprecipitated the mAChRs in a manner similar to an anti-m2 mAChR monoclonal antibody tested in parallel. The chagasic antibodies did not directly interact with the ligand binding site, because the binding of radiolabeled antagonist was unchanged by the addition of the chagasic IgG. In intact cells stably expressing the hm2 mAChR, the chagasic IgGs, but not normal IgGs, mimicked the ability of the agonist acetylcholine to induce two effects associated with agonist-induced receptor desensitization: a decrease in affinity for agonist binding to m2 mAChR and sequestration of the hm2 mAChRs from the cell surface. The results demonstrate that the chagasic IgGs can directly interact with and desensitize m2 mAChRs and provide support for the hypothesis of autoimmune mechanisms having a role in the pathogenesis of Chagas' cardioneuromyopathy.

Interaction of human chagasic IgG with the second extracellular loop of the human heart muscarinic acetylcholine receptor: functional and pathological implications.

Circulating antibodies from human and murine chagasic sera are able to interact with myocardium-activating neurotransmitter receptors. Here we reported the presence of autoantibodies against the second extracellular loop of the human heart muscarinic acetylcholine receptors (mAChR) in patients with Chagas' disease by using a synthetic 24-mer peptide in immunoblotting and enzyme immunoassay. Affinity-purified antipeptide IgG from chagasic patients, similar to monoclonal antihuman M2 mAChR, recognized bands with a molecular weight corresponding to the cardiac mAChR. The binding was inhibited by the peptide, assessing the specificity of the interaction. The antipeptide autoantibody also displayed an "agonist-like" activity modifying the intracellular events associated with mAChR activation, i.e., decreased contractility, increased cGMP, and decreased cAMP production. All of these effects on rat atria by chagasic antipeptide autoantibodies resemble the effects of the authentic agonist and those of the total polyclonal chagasic IgG, being selectively blunted by atropine and neutralized by the synthetic peptide corresponding in aminoacid sequence to the second extracellular loop of the human M2 mAChR. A clinical relevance of these findings is demonstrated by a strong association between the existence of circulating antipeptide autoantibodies in chagasic patients and the presence of dysautonomic symptoms, making these autoantibodies a proper early marker of heart autonomic dysfunction.

Increases in cyclic AMP levels couple to H1 receptors in atria from autoimmune myocarditis mice.

We have previously shown that myocardium from experimental autoimmune myocarditis expresses H1 receptors not present in normal mice heart. ThEA acting via H1 receptors, augments cyclic AMP production in atria from autoimmune myocarditis mice without any effect on atria from control mice. Addition of mepyramine before ThEA caused cyclic AMP levels to fall to a level similar to basal, confirming the H1 receptor participation. Histamine at low concentrations mimicked the ThEA action on H1 receptor-stimulation of cyclic AMP production by autoimmune myocardium. The fact that the inhibition of phospholipase C blocked the cyclic AMP stimulation by ThEA, supports the assumption that this action is secondary to receptor-mediated hydrolysis of phosphoinositides, generating some oxidative metabolites (IP3-DAG), which in turn may be responsible for the cyclic AMP effect. So, the inhibition of protein kinase C and calcium/calmodulin partially prevented the stimulatory action of ThEA on cyclic AMP levels in autoimmune myocardium, suggesting that both pathways are implicated in this effect. Data shows that the stimulation of H1 receptors by specific agonist in atria from autoimmune myocarditis mice, augments the cyclic AMP, requiring the hydrolysis of phosphoinositide cycle. The role of this cyclic AMP augmentation in myocardium from autoimmune myocarditis mice, will provide a basis to assess the role of this second messenger as an important factor in the regulation and/or modulation of the physiological behaviour of the heart in the course of autoimmune myocarditis.

Endogenous nitric oxide signalling system and the cardiac muscarinic acetylcholine receptor-inotropic response.

1. In this paper we have determined the different signalling pathways involved in muscarinic acetylcholine receptor (AChR)-dependent inhibition of contractility in rat isolated atria. 2. Carbachol stimulation of M2 muscarinic AChRs exerts a negative inotropic response, activation of phosphoinositide turnover, stimulation of nitric oxide synthase and increased production of cyclic GMP. 3. Inhibitors of phospholipase C, protein kinase C, calcium/calmodulin, nitric oxide synthase and guanylate cyclase, shifted the dose-response curve of carbachol on contractility to the right. These inhibitors also attenuated the muscarinic receptor-dependent increase in cyclic GMP and activation of nitric oxide synthase. In addition, sodium nitroprusside, isosorbide, or 8-bromo cyclic GMP, induced a negative inotropic effect, increased cyclic GMP and activated nitric oxide synthase. 4. These results suggest that carbachol activation of M2 AChRs, exerts a negative inotropic effect associated with increased production of nitric oxide and cyclic GMP. The mechanism appears to occur secondarily to stimulation of phosphoinositides turnover via phospholipase C activation. This in turn, triggers cascade reactions involving calcium/calmodulin and protein kinase C, leading to activation of nitric oxide synthase and soluble guanylate cyclase.

Experimental autoimmune myocarditis: a suitable model to study neuroimmune crosstalk.

This review regards the main functional characteristics of hearts subjected to an autoimmune response, focusing especially on the role of T lymphocytes and autoantibodies in the development of cardiac dysfunction. Evidence of a strong association in the onset and time-course of immune response and cardiac dysfunction is presented and the results are viewed comparatively with myocarditis models induced by heart, parasite or virus inoculation. Cardiac damage is evaluated regarding various aspects, namely histologic, immunologic, biochemical, pharmacologic, physiologic. Finally, the model, for its characteristics of resulting from an autoimmune response against the heart with functional consequences, has proved its usefulness to study neuroimmune interaction, mainly the immune to nervous direction, as autoantibodies and T cell-derived factors have a role in cardiac failure.

Experimental autoimmune myocarditis: a suitable model to study neuroimmune crosstalk.

This review regards the main functional characteristics of hearts subjected to an autoimmune response, focusing especially on the role of T lymphocytes and autoantibodies in the development of cardiac dysfunction. Evidence of a strong association in the onset and time-course of immune response and cardiac dysfunction is presented and the results are viewed comparatively with myocarditis models induced by heart, parasite or virus inoculation. Cardiac damage is evaluated regarding various aspects, namely histologic, immunologic, biochemical, pharmacologic, physiologic. Finally, the model, for its characteristics of resulting from an autoimmune response against the heart with functional consequences, has proved its usefulness to study neuroimmune interaction, mainly the immune to nervous direction, as autoantibodies and T cell-derived factors have a role in cardiac failure.

Identification of antibodies with muscarinic cholinergic activity in human Chagas' disease: pathological implications.

We examined the possible role of altered humoral immunity in dysautonomic syndrome in Chagas' disease by analyzing the effect of sera and IgG on the binding of radioligand to heart muscarinic cholinergic receptors and on the contractility of myocardium. Human Chagasic IgG inhibited in a non-competitive manner the binding of [3H]quinuclidinyl benzilate to the cardiac cell membrane. Moreover, human Chagasic IgG behaved as a partial muscarinic cholinergic agonist, reducing heartcontractility and inhibiting the action of pilocarpine. The prevalence of the cholinergic antibody activity was higher in sera from T. cruzi-infected asymptomatic individuals with dysautonomic syndrome than in those without autonomic nervous system alterations. The presence of these antibodies could explain the progressive receptor blockade in the parasympathetic branch of the autonomic nervous system, leading to dysautonomia.

Phosphoinositide hydrolysis mediated by H1 receptors in autoimmune myocarditis mice.

Stimulation of phosphoinositide hydrolysis in myocardium from autoimmune myocarditis mice by ThEA and histamine was assayed. Myocardium from autoimmune heart, but not the normal forms, specifically increased phosphoinositide turnover in the presence of histaminergic agonists. This increment was blocked by a specific H1 antagonist mepyramine and to the same extent by the phospholipase C inhibitor NCDC. By using a binding assay H1 histaminergic receptors were detected in autoimmune heart membrane preparations, but this was not observed in normal heart. These data suggest that autoimmune myocardium expressed a functional H1 receptor that could involve a distinctive mechanism operating in the disease.

Cholinergic response of isolated rat atria to recombinant rat interferon-gamma.

Addition of recombinant rat interferon-gamma (IFN-gamma) to beating rat atria decreased the contractile strength in a dose-dependent manner. The effect was specific of IFN-gamma since it was abrogated by monoclonal anti-rat IFN-gamma. It required the activation of the cholinergic system of the heart as inhibition of both nicotinic (10(-7) M hexametonium) and muscarinic cholinoceptors (10(-7) M atropine) prevented the reaction. Hemicholinium (2 x 10(-5) M) and tetrodotoxin (5 x 10(-7) M) also reduced the response. Likewise, IFN-gamma potentiated the action of the muscarinic agonist carbachol. IFN-gamma simulated the biological effect of cholinergic agonists because: (a) it increased cGMP formation; (b) it decreased cAMP formation; and (c) it reduced heart contractility at doses that can be considered physiologic. IFN-gamma also modified the muscarinic receptor by interfering with the binding of the radiolabelled antagonist quinuclidinyl benzilate [( 3H]QNB). It is suggested that IFN-gamma binding to IFN-gamma receptors in the heart may lead to a cholinergic response by interaction of both receptor systems on the surface of atrial cells.

Expression of alpha-adrenoceptors in a human transformed lymphoblastoid cell line.

The presence of alpha-adrenergic receptors (absent in normal lymphocytes) has been demonstrated in transformed human lymphocytes of the Raji cell line. Binding properties of beta-adrenergic receptors were similar to those reported for normal lymphocytes. A single population of alpha 2-adrenergic receptors was characterized in intact Raji lymphoblasts by binding and saturation assays with the alpha 2-adrenergic antagonist yohimbine. Competition curves with [3H]yohimbine indicate the presence of typical alpha 2-adrenoceptors. Reaction of Raji with the alpha 2-adrenergic agonist clonidine (10(-6) M) stimulated their growth rate. In contrast, the alpha 1-adrenergic agonist methoxamine (10(-6) M) had no effect. Previous work indicates that Raji can actively produce thromboxanes (TX) and that these decreased atrium contractility. In agreement with these results and with the binding studies, it is now shown that clonidine stimulation enhanced the negative inotropic effects of Raji on isolated rat atria. This reaction was prevented by incubation of Raji with yohimbine (10(-6) M) but not with the alpha 1-adrenergic antagonist prazosin (10(-6) M) or the beta-adrenergic antagonist propranolol (10(-7) M). The biologic effect of Raji on rat atria was probably due to production of cyclooxygenase metabolites of arachidonic acid, because it was blocked by preincubation of the cells with the cyclooxygenase inhibitors indomethacin (10(-6) M) and aspirin (10(-4) M) or the thromboxane synthetase inhibitors nictindol (10(-5) M) and imidazole (10(-4) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenergic cardiac antibody in autoimmune myocarditis.

Balb/c mice were immunized with homologous heart in complete Freund's adjuvant to induce autoimmune myocarditis. The myocarditis was characterized by lymphomononuclear infiltration, electrocardiographic abnormalities and antimuscle antibodies by indirect immunofluorescence. In this paper, we demonstrate that the IgG present in autoimmune myocarditis mice is able to bind to beta-adrenoreceptors of the heart and also induce a biological effect inhibiting the contractile action of exogenous norepinephrine. Auto-immune IgG inhibited the binding of (3H)-dyhidroalprenolol to a beta-adrenergic receptor of purified myocardial membranes behaving as non-competitive inhibitor. This IgG also exerted a non-competitive inhibition upon the mechanical effect of exogenous norepinephrine. The recognition appears to be organ specific, because the autoimmune myocarditis IgG did not bind to beta-lymphocyte, lung and fat adrenoreceptors. The autoimmune IgG inhibited the stimulatory action of isoproterenol on cAMP levels, behaving as a beta-adrenergic antagonist.

Role of beta 2-adrenoceptors in the biological effect of autoimmune orchitis spleen cells.

Autoimmune orchitis induced an increment in beta 2-adrenoceptor populations in intact mouse spleen lymphocytes. Normal and autoimmune lymphocytes incubated with soterenol increased the mechanical response of isolated atria. Autoimmune cells were more effective than normal cells in inducing this response. Soterenol or spleen cells alone did not modify the contractility at the concentration used. Inhibitors of beta 2-adrenoceptors of spleen cells completely blunted the reaction between soterenol and lymphocytes, while when atria were exposed to butoxamine, mechanical activity induced by soterenol plus lymphocytes was not affected. Cell-free supernatants of lymphocytes exposed to soterenol elicited the reaction in the same way as soterenol-treated lymphocytes. Direct contact of cells with the assay organ was not necessary. Inhibitors of cyclooxygenase on lymphocytes blocked the reaction of soterenol-treated lymphocytes on atria, while inhibitors of lipoxygenase(s) completely blocked the reaction of atria exposed to soterenol-stimulated lymphocytes or supernatants. These results suggest that soterenol reacts with beta 2-adrenoceptors of normal and autoimmune cells. From this reaction, soluble factors are released that in turn trigger stimulation of the atrial contractility as a consequence of the release of oxidative products of the lipoxygenase(s) pathway of arachidonic acid from atria. The high activity of atria in the presence of autoimmune spleen cells is probably related to the increment in number of beta 2-adrenoceptors of these cells.

Prostaglandins, cyclic AMP production and biological activity of alloimmune thymocytes.

The effect of alloimmunized non-adherent thymocytes on the spontaneous activity of the mouse atria was studied. BALB/c anti C3H non-adherent thymocytes induced negative inotropic effect on C3H atria. Cell-free supernatant from non-adherent thymocytes induced the same biological activity. This activity was blunted by the inhibition of non-adherent immune thymocytes' cyclo-oxygenase activity. PGE was present in higher amounts in free-cell supernatant from BALB/c anti C3H thymocytes plus C3H atria than in those from non-immune thymocytes. Intracellular levels of immune thymocytes cAMP are raised in comparison with those of normal thymocytes. It is proposed that alloantigen stimulates non-adherent thymocytes, increasing intracellular levels of cAMP and PGE. Immune thymocytes, release PGE upon recognition of the alloantigens expressed in the atria and this triggers a negative inotropic effect. The increment in immune thymocyte cAMP appears to be associated with the activation of thymocytes cyclo-oxygenase activity by alloimmunization.

Alloimmunization-induced changes in thymocytes' prostaglandin levels: a signal for the induction of biological activity.

The effect of BALB/c anti C3H non-adherent thymocytes on the spontaneous activity of isolated C3H mouse atria was studied. Immune non-adherent thymocytes alone induced negative inotropic action, while macrophages alone did not have any effect. The same kind of collaborative effect between both cells is described. Cell-free supernatants obtained from non-adherent immune cells incubated with C3H myocardium induced the same biological activity than immune non-adherent thymocytes indicating that a soluble factor is involved. Inhibition of non-adherent thymocytes' cyclo-oxygenase activity prevented the negative inotropic effect of immune cells or cell-free supernatants. In contrast, when the inhibitors were applied upon myocardium did not modify the response. Supernatants from immune thymocytes plus myocardium, release higher amount of PGE series than those from non-immune thymocytes. It is proposed that non-adherent thymocytes are able to synthesize and release PGE series upon recognition of alloantigens expressed by atria cells; which in turn triggers the negative inotropic effect.