Paradoxical dose-reponse curves

Ian Musgrave ANN-DR at
Thu Sep 28 22:11:45 EST 1995

G'Day Folks

 Matt Jones <jonesmat at> writes:
>From: Matt Jones <jonesmat at>
>Subject: Re: Paradoxical dose-reponse curves
>Date: 27 Sep 1995 17:21:53 GMT

>In article <drg-260995145542 at> Duke Groebe,
>drg at writes:
>>Do you suppose, then, that it is open-channel blocking or desensitization
>>that explains "paradoxical dose-reponse curves" by peptides?

>I don't know. There wasn't really enough information in the original post
>to figure out which peptides, what the response was, etc... I don't know
>much about peptides, but I think most of them act at G-protein coupled
>receptors. These also desensitize, and I think it's possible that high
>concentrations of peptides could block channels activated by the

>In my experience, desesntization (someday I'll learn how to spell it)
>doesn't usually give bell-shaped curves by itself, but it could if the
>state diagram of the system had certain properties. Like an extra binding
>site that preferentially promotes desensitization. I think that two
>binding sites, with different effects upon occupancy, are probably
>necessary to explain bell-shaped curves. Usually, I think desensitization
>just left-shifts the equilibrium D-R curve, and depresses the apparent
>max, as you pointed out.


There are a couple of models for bell shaped concentration response curves. 
One involves agonists stimulating a second receptor, for which the agonists 
have a lower affinty, which is physiologically anatgonistic to the first 
receptor. See Trends in Pharmacological Sciences (1994) Vol 15 (No 6), 
178-181. and Vol 15, (No 90, pg 321-322 for further discussion. (The examples 
are G-protein linked peptide receptors).


Ian Musgrave PhD. Prince Henry's Institute of Medical Research
Mail: PO Box 5152 Clayton, Vic 3168, Australia. FAX: +61 3 550 6125
E-mail: Ian.Musgrave at         Phone: +61 3 550 4286

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