IC50 vs Ki value difference?

[Memantine]

Hi,

I am wondering what this data about Cyclizine means?

IC50:	SR-2B: IC50 = 0.37 nM (human); mAChR M5: IC50 = 0.63 nM (human); mAChR M1: IC50 = 0.68 nM (human); Histamine H1 Receptor: IC50 = 38 nM (human); SR-2A: IC50 = 225 nM (human)
Ki Data:	Histamine H1 Receptor: Ki= 4.44 nM (human); SR-2A: Ki= 64 nM (human); mAChR M4: Ki= 119 nM (human); mAChR M3: Ki= 159 nM (human); Muscarinic acetylcholine receptor M1: Ki= 163 nM (human) Does it say that cyclizine is an antagonist at the receptors in this order? H1 > 5-HT2A > mAChR

 

[aced126]

An IC50 value tells you the concentration of a compound required to inhibit a certain biological response or function. A Ki value tells you how strongly the compound binds to the target protein.

 

[serotonin2A]

Sometimes people report binding data as IC50 values. Were the IC50 values from binding or functional studies?

 

[Memantine]

I don't know this is were i found it: http://www.scbt.com/datasheet-391816-casnumber-303-25-3.html

 

[serotonin2A]

I would guess the numbers are based on functional assays. But I wouldn't put too much stock in info posted on commercial websites -- it isn't uncommon to find errors. It's always best to dig through the primary literature to understand how the data was collected.