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Old 01-18-2013
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Question D1 receptors are excitatory via increased cAMP, right?

and D2 are inhibitory via 2 mechanisms:

1) decreased calcium conductance in presynaptic neuron

2) increased potassium conductance in postsynaptic neuron

its just that katzung says that BOTH D1 and D2 receptors are inhibitory. i understand how D2 are inhibitory by the 2 mechanisms above.


But if you have increased cAMP, then how are D1 receptors inhibitory too?
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Old 01-18-2013
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have you remembered D1 causes vasodilation of renal, mesentric, coronary vasculature by increasing the cAMP in pharma lecture
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Old 01-19-2013
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Quote:
Originally Posted by neha_subh View Post
have you remembered D1 causes vasodilation of renal,mesentric,coronary vasculature by increasing the cAMP in pharma lecture
yes, but that's for dopamine recentpors on sm. muscle. i'm talking about receptors in the CNS, sorry didn't make myself clear on that.

in the CNS, there are 2 mechanisms by which D2 receptors are inhibitory. one action on the post synaptic membrane, and the otehr on the presynaptic membrane.


as for D1, i know dopamine receptors are Glinked, so for D1, they are excitatory in BOTH the CNS and on sm. muscle?


at this point, i'm just really confused as to the Dopamine receptors, their locations, and the actions of their G-protein linked 2nd messengers in the cell.

i know ALL dopamine receptors are G-protien linked. but in the katzung book (for dopamine receptors of CNS), it says D1 is inhibitory, and mechanism is INCREASE in cAMP. this is confusing me!
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Old 01-19-2013
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i suppose another querstion i have relates to D1 receptors. i understand that d1 receptors on smooth muslce are Gs (stimulatory), but they do so by, increasing cAMP, but this causes smooth muscle relaxation.

what is the mechanism of action, between increase in cAMP and smooth muscle relaxation?
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Old 01-19-2013
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Quote:
Originally Posted by ReggieMiller View Post
i suppose another querstion i have relates to D1 receptors. i understand that d1 receptors on smooth muslce are Gs (stimulatory), but they do so by, increasing cAMP, but this causes smooth muscle relaxation.

what is the mechanism of action, between increase in cAMP and smooth muscle relaxation?
inc cAMP activates protein kinase A which phosphorylates MLCK resulting in its inactivation causing s m relaxation ; refer KLN pharm CVS section
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Old 01-19-2013
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Originally Posted by crusader View Post
inc cAMP activates protein kinase A which phosphorylates MLCK resulting in its inactivation causing s m relaxation ; refer KLN pharm CVS section
yeah but this is activated by calcium, and the cGMP is what causes relaxaction by dephosphorylating the myosin light chains.

nothing to do with cAMP or dopamine receptors from what i see.
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Old 01-19-2013
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I have decided to just keep things simple. i'm not sure if katzung is a typo or not, but just to post it again, this is what katzung says for CNS dopamine receptors:

D1 receptors are inhibitory via increased cAMP

i think since this is the CNS, perhaps that's why things work a little different?

For now, i'm just going to remember that:

D1 receptors are Stimulatory via increased cAMP (Gs linked), and..

D2 receptors are Inhibitory via decreased cAMP (Gi linked).
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Old 01-19-2013
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Quote:
Originally Posted by ReggieMiller View Post
I have decided to just keep things simple. i'm not sure if katzung is a typo or not, but just to post it again, this is what katzung says for CNS dopamine receptors:

D1 receptors are inhibitory via increased cAMP

i think since this is the CNS, perhaps that's why things work a little different?

For now, i'm just going to remember that:

D1 receptors are Stimulatory via increased cAMP (Gs linked), and..

D2 receptors are Inhibitory via decreased cAMP (Gi linked).
how phosphodiestrase inhibitors(theophyline and inamrinone) works ---increases the cAMP---Phosphorylates the MLCK(inactive)---thereby relax the smooth muscle
B2-Agonist-----activates the adenylate cyclase thereby inc.cAMP--MLCK Phosphorylates (inactive)------relax the smooth muscle..

simply remember things in that way
try to make things simple dont confuse yourself in high yield stuff (katzung,harper etc)..
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Old 01-20-2013
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D1 in the CNS is an inhibitor because it disinhibition the inhibitor (indirect pathway) making it stimulatory.
And also stimulated the excitatory pathway.

So D1 excites direct pathway. And inhibits indirect pathway.
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Old 01-20-2013
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Quote:
Originally Posted by SOBE223 View Post
D1 in the CNS is an inhibitor because it disinhibition the inhibitor (indirect pathway) making it stimulatory.
And also stimulated the excitatory pathway.

So D1 excites direct pathway. And inhibits indirect pathway.
as i remembered D2 is inhibitory in CNS, While D1 Is excitatory in CNS
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Old 02-04-2015
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DOPAMINE RECEPTORS
D1 -like: Gs coupled
D2-like: Gi coupled
> D2A: nigrostriatal
> D2c: mesolimbic

-Kaplan Pharma
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