Amy asked in Science & MathematicsChemistry · 2 months ago

In pharmacology, why does EC50 not necessarily equal Kd?

I have the EC50 for nicotine stimulation of [3H]-

dopamine release, this value does not necessarily equal the Kd value for

nicotine at the receptor binding sites. Why?

1 Answer

  • 2 months ago

    If the relationship between receptor occupancy and response is linear, then the EC50 would equal the Kd, but it's a little more complex than that.  Consider spare receptors for example.  The EC50 may not represent binding to half of the total number of receptors, where in a binding assay, the Kd does involve all the receptors.  I could go on with various other examples (partial agonists/antagonists, etc.), but hopefully this gives you some idea as to why these two measurements may not be equal.

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