The detection of the non-M2 muscarinic receptor subtype in the rat heart atria and ventricles.
Mammal heart tissue has long been assumed to be the exclusive domain of the M(2) subtype of muscarinic receptor, but data supporting the presence of other subtypes also exist. We have tested the hypothesis that muscarinic receptors other than the M(2) subtype are present in the heart as minor populations. We used several approaches: a set of competition binding experiments with pirenzepine, AFDX-116, 4-DAMP, PD 102807, p-F-HHSiD, AQ-RA 741, DAU 5884, methoctramine and tripinamide, blockage of M(1) muscarinic receptors using MT7 toxin, subtype-specific immunoprecipitation experiments and determination of phospholipase C activity. We also attempted to block M(1)-M(4) receptors using co-treatment with MT7 and AQ-RA 741. Our results show that only the M(2) subtype is present in the atria. In the ventricles, however, we were able to determine that 20% (on average) of the muscarinic receptors were subtypes other than M(2), with the majority of these belonging to the M(1) subtype. We were also able to detect a marginal fraction (6 +/- 2%) of receptors that, based on other findings, belong mainly to the M(5) muscarinic receptors. Co-treatment with MT7 and AQ-RA 741 was not a suitable tool for blocking of M(1)-M(4) receptors and can not therefore be used as a method for M(5) muscarinic receptor detection in substitution to crude venom. These results provide further evidence of the expression of the M(1) muscarinic receptor subtype in the rat heart and also show that the heart contains at least one other, albeit minor, muscarinic receptor population, which most likely belongs to the M(5) muscarinic receptors but not to that of the M(3) receptors.
Myslivecek
Jaromir
J
Institute of Physiology, 1st Faculty of Medicine, Charles University, Albertov 5, 12800, Prague, Czech Republic. jmys@lf1.cuni.cz
Klein
Martin
M
Novakova
Martina
M
Ricny
Jan
J
D000818:Animals; D001667:Binding, Competitive; D015870:Gene Expression; D006325:Heart Atria / Q000187:drug effects / Q000378:metabolism*; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D043643:Receptor, Muscarinic M1 / Q000187:drug effects / Q000378:metabolism; D043585:Receptor, Muscarinic M2 / Q000187:drug effects / Q000378:metabolism; D043587:Receptor, Muscarinic M3 / Q000187:drug effects / Q000378:metabolism; D043642:Receptor, Muscarinic M5 / Q000187:drug effects / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism
D043643:Receptor, Muscarinic M1; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D043642:Receptor, Muscarinic M5; D011976:Receptors, Muscarinic; D010738:Type C Phospholipases