Biochemical alterations of the cardiac muscarinic binding sites have not been correlated with physiological observations. The development of responsiveness to acetylcholine in the fetal mouse heart occurs during the third trimester. We tested the hypothesis that the altered physiological response was related to changes in the muscarinic cholinergic binding site assayed by using the potent antagonist [3H]-quinuclidinyl benzilate (QNB). Analysis of saturation isotherms of specific (atropine displaceable) [3H]-QNB binding gave an apparent dissociation constant (KDapp) of 27 ± 3 (SEM) pM for adult heart. Receptor density increased significantly during the third trimester of pregnancy to 48% of adult, while the KDapp did not change. The increase in receptor density parallels the demonstrated increased responsiveness to acetylcholine.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Pharmacology, Toxicology and Pharmaceutics(all)