TY - JOUR T1 - Expression of Multiple Subtypes of Muscarinic Receptors and Cellular Distribution in the Human Heart JF - Molecular Pharmacology JO - Mol Pharmacol SP - 1029 LP - 1036 DO - 10.1124/mol.59.5.1029 VL - 59 IS - 5 AU - Huizhen Wang AU - Hong Han AU - Liming Zhang AU - Hong Shi AU - Gernot Schram AU - Stanley Nattel AU - Zhiguo Wang Y1 - 2001/05/01 UR - http://molpharm.aspetjournals.org/content/59/5/1029.abstract N2 - Five isoforms of the muscarinic acetylcholine receptor (mAChR) have been identified by molecular cloning and designated m1–m5, of which four correspond to the functional subtypes M1, M2, M3, and M4 in primary tissues. The presence of M5receptors in tissues remains uncertain. The present study was designed to explore the diversity and cellular distribution of various mAChR subtypes in human hearts. Competition binding of [N-methyl-3H]-scopolamine methyl chloride with various mAChR antagonists yielded data consistent with the presence of multiple subtypes (M1/M2/M3/M5) of mAChRs in both human atrial (HA) and ventricular (HV) tissues. Expression of mRNAs encoding all five subtypes was readily detected by reverse transcription-polymerase chain reaction in both HA and HV samples. Immunoblotting with subtype-specific antibodies confirmed the presence of M1, M2, M3, and M5, but not M4, proteins in membrane preparations from both HA and HV. The protein levels of M1 and M2 were comparable between HA and HV. Although the density of M3appeared ∼10-fold higher in HV than HA, that of M5 was ∼5 times lower in HV than in HA. Positive immunostaining of single ventricular myocytes by M1, M2, M3, and M5 antibodies, respectively, was consistently detected. Under confocal microscopy, M5 showed characteristic localization to the intercalated discs, whereas other subtypes were more evenly distributed throughout the surface membrane. Our results provide the first molecular evidence for the presence of multiple subtypes of mAChR, including endogenous M5 receptors, in human hearts and suggest that different subtypes have different tissue distributions and cellular localization. ER -