Differential ontogeny of putative M1 and M2 muscarinic receptor binding sites in the murine cerebral cortex and heart

R. A. Evans, M. Watson, H. I. Yamamura, W. R. Roeske

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


Studies with [3H]pirenzepine ([3H]PZ) suggest that this nonclassical muscarinic antagonist selectively identifies putative M1 muscarinic receptors. We now compare the ontogeny of these putative M1 sites, identified by high-affinity [3H]PZ binding, with sites identified by the classical antagonist (-)-[3H]quinuclidinyl benzilate {(-)-[3h]QNB}) in murine cerebral cortical and cardiac homogenates. Dissociation constants (K(d)) for [3H]PZ (2.1-6 nM in the cortex and 2.0-21 nM in the heart) and for (-)-[3H]QNB (10-28 pM in the cortex and 10-39 pM in the heart) are similar in adult and neonatal tissues, whereas receptor density (maximum binding, femtomoles per milligram of protein) varies significantly. Cerebral cortical [3H]PZ binding rises from 14% at birth, to 88% of adult levels by day 14, peaks at 128% at day 28 and falls to the mean adult level of 606 fmol/mg of protein. Cerebral cortical (-)[3H]QNB binding parallels [3H]PZ binding. Conversely, parallel studies show cardiac (-)-[3H]QNB density is 3- to 17-fold greater than the comparable density of high-affinity [3H]PZ binding sites throughout ontogeny. We conclude that: 1) the high ratio of [3H]PZ binding to (-)-[3H]QNB binding identifies the murine cerebral cortex as a tissue which contains predominantly putative M1 muscarinic binding sites; 2) the relatively low ratio of [3H]PZ binding to (-)-[3H]QNB binding throughout ontogeny identifies the murine heart as a tissue which contains primarily the putative M2 muscarinic binding site; and 3) M1 and M2 receptor binding sites show distinct developmental curves in the cerebral cortex and heart. In the postnatal period, cerebral cortical M1 receptor density rises rapidly whereas cardiac M2 density shows little change. These data support the concept of distinct muscarinic receptor subtypes.

Original languageEnglish (US)
Pages (from-to)612-618
Number of pages7
JournalJournal of Pharmacology and Experimental Therapeutics
Issue number3
StatePublished - 1985

ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology


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