Abstract
The aim of the present study was to investigate the binding affinities and dissociation potencies of several 5-HT2 antagonists in M2 muscarinic receptor of rat heart membranes using [3H]QNB as a radioligand. The 5-HT2 antagonists used in this study were sarpogrelate, ketanserin and cyproheptadine. The results showed that sarpogrelate and ketanserin had very weak binding affinities to M2 muscarinic receptor, whereas cyproheptadine had higher binding affinity to this receptor than the muscarinic receptor antagonist, atropine. All of these three 5-HT2 antagonists as well as muscarinic receptor antagonists (atropine and pirenzepine) were readily dissociated from M2 muscarinic receptor in rat heart membranes after washing. Therefore, the findings of the present investigation suggest that the dissociation potencies of neither 5-HT2 antagonists nor muscarinic antagonists used correlate with their binding affinities to M2 muscarinic receptors in rat heart.
