Agonists and antagonists induce different palonosetron dissociation rates in 5-HT?A and 5-HT?AB receptors.

ABSTRACT: Palonosetron is a potent 5-HT? receptor antagonist with a unique structure and some unusual properties. Here we explore the properties of palonosetron at heterologously expressed 5-HT?A and 5-HT?AB receptors. We used receptors expressed in HEK293 cells, and functionally analysed them using a membrane potential sensitive dye in a Flexstation, which revealed IC??s of 0.24 nM and 0.18 nM for 5-HT?A and 5-HT?AB receptors respectively. Radioligand binding studies with [(3)H]palonosetron revealed similar Kds: 0.34 nM for 5-HT3A and 0.15 nM for 5-HT?AB receptors. Kinetic studies showed palonosetron association and dissociation rates were slightly faster in 5-HT?AB than 5-HT?A receptors, and for both subtypes dissociation rates were ligand-dependent, with antagonists causing more rapid dissociation than agonists. Similar ligand effects were not observed for [(3)H]granisetron dissociation studies. These data support previous studies which show palonosetron has actions distinct to other 5-HT3 receptor antagonists, and the slow rates observed for agonist induced dissociation (t?/? > 10 h) could at least partly explain the long duration of palonosetron effects in vivo.

SUBMITTER: Lummis SC 

PROVIDER: S-EPMC3778450 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature