Summary
The muscarinic receptor present in chicken cardiac membranes was characterised using a ligand binding approach and compared to the M1, M2 and M3 receptors that can be identified in ligand binding studies at present. [3H]N-methylscopolamine and [3H]pirenzepine appeared to label the same population of muscarinic receptors in chicken cardiac membranes since the density of sites labeled by the two radioligands was similar. Furthermore, affinity estimates of 8 muscarinic receptor antagonists for chicken cardiac muscarinic receptors were the same irrespective of whether [3H]N-methylscopolamine or [3H]pirenzepine was used as the radioligand. The chicken cardiac muscarinic receptor displayed high affinity for pirenzepine (pK i = 7.9) and so did not appear to represent an M2 receptor. Despite the high affinity of chicken cardiac muscarinic receptors for pirenzepine, affinity estimates for dicyclomine (pK i = 8.0), CPPS (pK i = 8.4) and 4DAMP (pK i = 8.6) in chicken heart were not consistent with the presence of M1 receptors. The chicken cardiac muscarinic receptor also displayed significant differences to the M3 receptor since it displayed high affinity for AF-DX 116 (pK i = 7.1) and methoctramine (pK i = 8.4). Finally, chicken heart muscarinic receptors displayed high affinity for gallamine (pK i = 7.0) and pirenzepine suggesting that the receptor was different to the M4 muscarinic receptor of the NG108-15 cell line. These findings suggest that chicken heart expresses a novel muscarinic receptor subtype distinct from the M1, M2, M3, and M4 subtypes already described.
Similar content being viewed by others
References
Barnard EA (1988) Separating receptor subtypes from their shadows. Nature 335:301–302
Birdsall NJM, Hulme EC, Keene M (1986) The binding of pirenzepine to digitonin-solubilized muscarinic acetylcholine receptors from the rat myocardium. Br J Pharmacol 87:307–316
Bonner TI, Buckley NJ, Young AC, Brann MR (1987) Identification of a family of muscarinic acetylcholine receptor genes. Science 237:527–532
Bonner TI, Young AC, Brann MR, Buckley NJ (1988) Cloning and expression of the human and rat m5 muscarinic acetylcholine receptor genes. Neuron 1:403–410
Brown TH, Goldstein D, Masters SB (1985) The putative M1 muscarinic receptor does not regulate phosphoinositide hydrolysis. Studies with pirenzepine and McN-A343 in chick heart and astrocytoma cells. Mol Pharmacol 27:525–531
Cheng Y-C, Prusoff WH (1973) Relationship between the inhibitio constant (KI) and the concentration of inhibitor which causes 50% inhibition (IC50) of an enzymatic reaction. Biochem Pharmacol 22:3099–3108
Choo LK, Mitchelson F, Napier P (1988) Differences in antagonist affinities at the muscarinic receptors in chick and guinea-pig. J Autonom Pharmacol 8:259–266
De Jonge A, Doods HN, Riesbos J, Van Zwieten PMBW (1986) Heterogeneity of muscarinic receptor binding sites in rat brain, submandibular gland and atrium. Br J Pharmacol 89 (Suppl): 551P
Delmendo R, Michel AD, Whiting RL (1989) Affinity estimates of muscarinic receptor antagonists for three putative muscarinic receptor subtypes. Br J Pharmacol 96:457–464
Eglen RM, Whiting RL (1986) Muscarinic receptor subtypes: A critique of the current classification and a proposal for a working nomenclature. J Autonom Pharmacol 5:323–346
Hammer R, Giachetti A (1982) Muscarinic receptor subtypes: M1 and M2. Biochemical and functional characterization. Life Sci 31:2991–2994
Jeck D, Lindmar R, Löffelholz K, Wanke M (1988) Subtypes of muscarinic receptor on cholinergic nerves and atrial cells of chicken and guinea-pig hearts. Br J Pharmacol 93:357–366
Kwarta MM, Ptasienski J, Hosey MM (1988) Agonist-induced phosphorylation of the pig-atrial muscarinic receptor and its comparison with the chick heart receptor. FASEB J 2:A624
Michel AD, Whiting RL (1988) Methoctramine, a polymethylene tetraamine, differentiates three subtypes of muscarinic receptor in direct binding studies. Eur J Pharmacol 145: 61–66
Michel AD, Delmendo R, Stefanich E, Whiting RL (1989) Pharmacological analysis of the muscarinic receptor subtype of the NG108-15 cell line. Naunyn-Schmiedeberg's Arch Pharmacol (in press)
Peralta EG, Ashkenazi A, Winslow JW, Smith DH, Ramachandran J, Capon DJ (1987) Distinct primary structures, ligand binding properties and tissue specific expression of four human muscarinic acetylcholine receptors. EMBO J 6:3923–3929
Sera M, Lei M, Roeske WR, Lui GK, Watson M, Yamamura HI (1988) The intact human neuroblastoma cell (SH-SY5Y) exhibit high affinity [3H]pirenzepine binding associated with hydrolysis of phosphatidylinositols. J Neurochem 50:1513–1521
Soroto S, Adam LP, Pappano AJ (1986) Comparison of muscarinic receptor properties in hatched chick heart atrium and ventricle. J Pharmacol Exp Ther 236:602–609
Author information
Authors and Affiliations
Additional information
Send offprint requests to A. Michel.
Rights and permissions
About this article
Cite this article
Michel, A.D., Whiting, R.L. Radioligand binding characteristics of the chicken cardiac muscarinic receptor. Naunyn-Schmiedeberg's Arch Pharmacol 340, 279–284 (1989). https://doi.org/10.1007/BF00168511
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00168511