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Dr. Bob is Robert Hsiung, MD,
[email protected]Shown: posts 1 to 8 of 8. This is the beginning of the thread.
Posted by linkadge on January 18, 2004, at 9:25:27
Does anyone here know what an 'inverse agonist' is, or what a 'partial agonist' is.
Posted by SLS on January 18, 2004, at 11:05:23
In reply to inverse agonist,- partial agonist ??, posted by linkadge on January 18, 2004, at 9:25:27
> Does anyone here know what an 'inverse agonist' is, or what a 'partial agonist' is.
A partial agonist binds to a receptor (strongly or weakly), but doesn't always stimulate it to perform its function. Sometimes it does and sometimes it doesn't I don't know the molecular details, but perhaps there are variable allosteric interactions that occur upon binding.
An inverse agonist of a receptor produces an effect opposite to what would occur upon stimulation. I guess an example of that would be the resting potential of a neuron (values are not physiological). Let us say that without receptor stimulation, the intrinsic resting potential of the cell is 5V. Upon stimulation of the receptors, the potential increases to 10V, the threshold upon which the neuron fires. When an inverse agonist binds to these same receptors, the potential of the cell drops to 2V. Now, in order to get the cell to fire, it will take a greater number of receptors to be stimulated in order to reach the 10V threshold. It will take an additional 8V in order to make up for the number of receptors affected by the inverse agonist.
I hope that helped.
- Scott
Posted by linkadge on January 18, 2004, at 13:15:37
In reply to Re: inverse agonist,- partial agonist ??, posted by SLS on January 18, 2004, at 11:05:23
So an inverse agonist would have similar functions to a antagonist. Ie they might have similar actions ?
Linkadge
Posted by SLS on January 18, 2004, at 14:10:22
In reply to Re: inverse agonist,- partial agonist ??, posted by linkadge on January 18, 2004, at 13:15:37
> So an inverse agonist would have similar functions to a antagonist. Ie they might have similar actions ?
>
> Linkadge
I'm having a difficult time explaining this. Certainly, an antagonist and an inverse agonist can produce similar outcomes. Both prevent the agonist from activating the receptor. However, the inverse agonist actually turns the receptor in the negative direction.
Another feeble analogy:An agonist shifts a car into gear and the car moves forward. An antagonist prevents the car from shifting and the car does not move. An inverse agonist shifts the car into reverse and the car moves backwards.
- Scott
Posted by linkadge on January 18, 2004, at 19:04:38
In reply to Re: inverse agonist,- partial agonist ??, posted by SLS on January 18, 2004, at 14:10:22
linkadge
Posted by Larry Hoover on January 20, 2004, at 9:20:29
In reply to inverse agonist,- partial agonist ??, posted by linkadge on January 18, 2004, at 9:25:27
> Does anyone here know what an 'inverse agonist' is, or what a 'partial agonist' is.
I'm typing briefly....broken arm. Inverse agonists bind to a receptor for a known agonist, but incite an inverse reaction. An example is beta-carboline, which binds to the GABA receptor, but induces anxiety and increases risk of seizure.
Partial agonists also bind to the receptor, but induce a response quantifiably lower than that of a full agonist. E.g. niacinamide on the GABA receptor.
In both cases, the "interfering" substance will also exhibit some effects due to antagonism, because the receptors generally cannot interface with the natural ligand while these substances are bound (competitive inhibition).
To determine these fine distinctions, you need also to understand the two-state model of receptor conformation, and that some receptors (e.g. GABA) are partially on, even in the absence of the ligand. There are likely to be genetic and environmental factors influencing the balance between the two receptor states, apart from substances binding to them, which may account for the variability in response to receptor-binding drugs.
More:
http://www.umu.se/pharm-neuro/inst/UmePharmacodynamics.pdf
http://www.anaesthetist.com/physiol/basics/receptor/receptor.htmLar
Posted by SLS on January 20, 2004, at 10:38:34
In reply to Re: inverse agonist,- partial agonist ?? » linkadge, posted by Larry Hoover on January 20, 2004, at 9:20:29
Woo Hoo!
Larry's back!
Posted by Larry Hoover on January 20, 2004, at 11:29:33
In reply to Re: inverse agonist,- partial agonist ?? » Larry Hoover, posted by SLS on January 20, 2004, at 10:38:34
> Woo Hoo!
>
> Larry's back!Sorry to confuse the issue.
http://www.dr-bob.org/babble/admin/20040112/msgs/303199.htmlI tried to email you. Didn't work I guess.
Lar
This is the end of the thread.
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