Assessment of affinities and dissociation potencies of several 5-HT2 antagonists to and from M2 muscarinic receptor in rat heart membranes.

Abstract

The aim of the present study was to investigate the binding affinities and dissociation potencies of several 5-HT(2) antagonists in M(2) muscarinic receptor of rat heart membranes using [(3)H]QNB as a radioligand. The 5-HT(2) antagonists used in this study were sarpogrelate, ketanserin and cyproheptadine. The results showed that sarpogrelate and ketanserin had very weak binding affinities to M(2) muscarinic receptor, whereas cyproheptadine had higher binding affinity to this receptor than the muscarinic receptor antagonist, atropine. All of these three 5-HT(2) antagonists as well as muscarinic receptor antagonists (atropine and pirenzepine) were readily dissociated from M(2) muscarinic receptor in rat heart membranes after washing. Therefore, the findings of the present investigation suggest that the dissociation potencies of neither 5-HT(2) antagonists nor muscarinic antagonists used correlate with their binding affinities to M(2) muscarinic receptors in rat heart.