Human chagasic IgGs bind to cardiac muscarinic receptors and impair L-type Ca2+ currents.
OBJECTIVE
Antibodies against cardiac G protein-coupled receptors have been reported in sera from chronic chagasic patients (CChP) and other non-parasitic cardiomyopathies, but the effects and underlying mechanism of interaction between these antibodies and heart cells are not fully established. To address this point, binding of antibodies purified from sera of CChP patients and normal blood donors (NBD) to cardiac muscarinic acetylcholine receptors (mAChR) and their effect on L-type Ca(2+) currents were examined.


RESULTS
Saturation [3H]NMS binding experiments with porcine atrial membranes showed that B(max) in the presence of CChP-immunoglobulin G (IgG) decreased from 280.2+/-16.08 fmol/mg (control) to 91.00+/-5.98 fmol/mg, with no apparent change in K(D), while NBD-IgG did not significantly alter these parameters. At the single channel level, CChP-IgG decreased both the fast and slow mean open times and P(o) (from 0.074+/-0.023 to 0.025+/-0.007) without changes in single channel conductance. I/V plots of isoproterenol-stimulated whole-cell L-type Ca(2+) currents (I(Ca)) from rabbit ventricular cardiomyocytes showed a significant reduction in peak I(Ca) during perfusion with CChP-IgG (at 0 mV: from 10.61+/-2.97 to 8.45+/-2.54 pA/pF). NBD-IgGs had no effect on I(Ca). A CChP-IgG purified against a peptide corresponding to the second extracellular loop of the M(2) receptor also impaired L-type Ca(2+) currents. All effects of CChP-IgG were blocked by atropine.


CONCLUSIONS
Our results show that antibodies from CChP bind to mAChR in a non-competitive manner and are able to activate the receptor in an agonist-like form resulting in L-type Ca(2+) current inhibition.
Hernández
Ciria Carolina Quintero
CC
Instituto de Biofísica Carlos Chagas Filho, Universidade do Brasil, Rio de Janeiro, Brazil.
Barcellos
Luciane Claudia
LC
Giménez
Luis Eduardo Díaz
LE
Cabarcas
Rafael Armando Bonfante
RA
Garcia
Simone
S
Pedrosa
Roberto Coury
RC
Nascimento
Jose Hamilton Matheus
JH
Kurtenbach
Eleonora
E
Masuda
Masako Oya
MO
Campos de Carvalho
Antonio Carlos
AC
D000818:Animals; D000906:Antibodies / Q000276:immunology*; D001285:Atropine / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D016022:Case-Control Studies; D002598:Chagas Cardiomyopathy / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011485:Protein Binding; D011817:Rabbits; D011950:Receptors, Cholinergic / Q000378:metabolism*
D000906:Antibodies; D020746:Calcium Channels, L-Type; D007074:Immunoglobulin G; D011950:Receptors, Cholinergic; D001285:Atropine; D007545:Isoproterenol