Stimulatory activity of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic receptors.
OBJECTIVE
To study the activity of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic receptors on cAMP production and inward calcium currents (Ica) in guinea pig ventricular myocytes. A comparison was also made with those of a muscarinic receptor agonist.


METHODS
cAMP content was determined by radioimmunoassay and the Ica in guinea pig single ventricular cells were recorded by the whole-cell patch clamp technique.


RESULTS
Both the muscarinic receptor agonist, carbachol (Carb 10 mumol/L), and anti-peptide antibodies (Abs 100 nmol/L) could decrease basal cAMP levels (by 46.9% +/- 4.2% and 60.2% +/- 4.6%, respectively) and basal Ica. Both Carb (10 mumol/L) and Abs (100 nmol/L) could also inhibit the isoprenaline-induced (Iso 0.8 mumol/L) increases in cAMP production (from 108.2 +/- 7.0 to 88.4 +/- 7.2 pmol/mg.protein/min for Carb and 88.6 +/- 5.1 pmol/mg.protein/min for Abs, respectively) and the increases in Ica. The muscarinic receptor antagonist atropine (Atr) was able to prevent these effects of Carb and Abs.


CONCLUSIONS
Anti-peptide antibodies against an epitope located in the second extracellular loop of human M2 muscarinic receptors, similar to muscarinic receptor agonist, could decrease the basal Ica and beta-receptor agonist stimulated increase of Ica by decreasing the basal and beta-receptor agonist stimulated increase of cAMP production, and therefore could have an effect on their target receptor. These results further suggest that autoimmunity may participate in the pathogenesis of human cardiomyopathy and the second extracellular loop of human M2 muscarinic receptor could be the main immunodominant region.
Wang
W
W
Department of Cardiothoracic Surgery, Second Hospital of Shanxi Medical University, Taiyuan 030001, China.
Guo
G
G
Tang
J
J
Li
J
J
Zhao
R
R
Hjalmarson
A
A
Fu
L X
LX
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000276:immunology*; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis*; D005260:Female; D006168:Guinea Pigs; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000276:immunology*; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic / Q000276:immunology*
D000906:Antibodies; D010446:Peptide Fragments; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic; D001285:Atropine; D002217:Carbachol; D000242:Cyclic AMP; D002118:Calcium