no spare receptors

[Miracoli]

In a system that does not contain spare receptors, drug X is an agonist and drug Y does not produce any
action by itself but decreases the effect of drug X by binding to a different site. Which of the following graphs represent the effect of drug Y, in which the first curve is drug X alone and the other 2 curves are drug X plus increasing doses of drug Y?

A)A
B)B
C)C
D)none of the graphs

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[acciddropping]

D?

 

[ulikedaggers]

B

 

[notbobtrustme]

looks like B

 

[ChessMaster3000]

looks like B

I think D--the Km should be the same for noncompetitive inhibitors, and B shows increasing Km.

 

[lovemango]

I'm gonna say D, it should look like graph B in this image: http://tmedweb.tulane.edu/pharmwiki/lib/exe/fetch.php/fig9_basicprinciples.png?w=800. Non-competitive antagonists reduce the Emax, but Km (affinity) should be the same since it binds to a different site.

 

[ulikedaggers]

Non-competitive antagonists can affect the potency (Km). It's not exactly the same situation as a non-competitive inhibitor.. at least that's what we learned.

 

[sanj238]

In this case since there are no excess, then I think it is D because increasing concentration wont change activity since all them are in use. It should really be zero order kinetics with just a straight line. the drug should just decrease the lines thereafter but they are all straight.