Are _forskolin_ and _U69593_ cAMP inhibitors?

[Chris Barry]

> 
> I think that kappa opioid receptors are belived to couple via pertussis
> toxin-sensitive Gi/Go proteins to the inhibition of calcium channels.
> Now, Gi can also inhibit adenylyl cyclase, and there is evidence that Go
> can do the same.  So that could explain an inhibitory effect on [cAMP] by
> U69593.
> 
> AJW
> 

Aren't 4 Ca++ 's required for maximal AC activity? If so, A receptor
that activates the adenylate cyclase via the inositol pathway could be
inhibited by a Ca++ channel blocker. ie:

   Ligand --> receptor 
                  |            DAG 
                  \/            |                          ???   
                Gp-prot-----> phospolipase c---->C-kinase------>Adeny-
                                |                     ^         late                                                             
                                \/                    |         Cyclase 
                               IP3---ER--->Ca++       | 
                                      ^   release-----|  
                                      | 
                                     U69593 (?)

Comments/criticisms appreciated

Chris