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I have a seemingly easy question to which I am having
difficulty getting an answer.
My question concerns how a drug binds to multiple
For example, epinephrine at low doses activates beta2,
and at high doses it activates alpha1.
The question is, at high doses, is it ONLY activating
alpha1, or is it having some maximized or saturable
effect on beta1 such that it can spill over to alpha1?
Preskorn gives an example of venlafaxine, which binds
to the serotonin and norepinephrine transporters. He
makes the point that at one dose it is essentially
binding only to the serotonin transporter, and at a
higher dose it begins to bind to the NET.
So if a drug binds to three systems with Ki 1x, 10x,
and 100x, does that mean that at the lowest dose it
only binds to the 1x system, and at a higher dose it
only binds to the 1x and 10x, and at a higher dose it
binds to all three? And, at the highest doses, the 1x
system's effects are "maximized?"
But the real question is, how can one calculate the
relative binding given Kis (or some other factor?)
Thanks in advance for your help.
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