Immunization with an M2ACh-R-derived peptide in mice enhanced the parasympathetic response to carbachol and attenuated the heart rate increase induced by atropine, gallamine, and isoproterenol.
Autoantibodies in vitro modulating the M2 acetylcholine receptor (M2ACh-R) were observed in patients with idiopathic dilated cardiomyopathy (IDC) or Chagas' cardiomyopathy (ChC). We investigated the in vivo consequences on heart rate of such antibodies in mice immunized with a peptide derived from the second extracellular loop of the M2ACh-R compared with mice immunized with an irrelevant peptide. Sera of mice immunized with the M2ACh-R-derived peptide recognized the M2ACh-R on immunoblots and enhanced agonist activity of carbachol toward the M2AChR transfected in CHO cells. In vivo, no difference could be shown in heart rate or heart rate variability between the two groups of mice. The decrease in heart rate induced by carbachol was more pronounced, however, in the M2ACh-R immunized mice. The increase in heart rate induced by atropine, gallamine, and isoproterenol was significantly attenuated in the M2ACh-R immunized mice. Analysis of heart rate variability further argued for an increased parasympathetic response to different drugs in the M2ACh-R immunized mice. Antibodies raised against the M2AChR can behave as positive M2AChR allosteric modulators in vivo. They might be protective in boosting the activity of the parasympathetic drive to the heart, especially in patients with a high sympathetic tone.
Peter et al. (2005) studied Animal model (context of idiopathic dilated cardiomyopathy or Chagas' cardiomyopathy). Immunization with M2ACh-R-derived peptide vs. Immunization with an irrelevant peptide was evaluated on Heart rate and heart rate variability. Immunization with an M2ACh-R-derived peptide in mice enhanced the parasympathetic response to carbachol and attenuated the heart rate increase induced by atropine, gallamine, and isoproterenol.