Forskolin-stimulated activity inhibition

Fig. 8. Enhanced signaling of the a2ALys251 polymorphic receptor. Adenylyl cyclase activities were determined in the presence of 5.0 pM forskolin and the indicated concentrations of the full agonist epinephrine. Results as shown are the percentage inhibition of forskolin-stimulated activities from clones at matched levels of expression (-2500 fmol/mg)., p < 0.05 for the maximal inhibition compared with wild-type for both agonists. (From ref. 22 with permission.)...

Adenylyl Cyclases. Figure 4 Regulation of adenylyl cyclases by G-proteins. Abbreviations Hs, Hj, Rs, and Rj denote hormones and receptors that lead to stimulation or inhibition, respectively, of adenylyl cyclases, Ca and Ci are active and inactive configurations of adenylyl cyclase, Fo forskolin binding site, Gs and Gj are GTP-dependent regulatory proteins comprising their respective as, and (3y subunits. 

One of the best-characterized effectors and second messenger systems is the cAMP cascade that can be either activated or inhibited by neurotransmit-ter/neuropeptide receptors, including those implicated in anxiety/stress such as CRE Receptors that activate cAMP synthesis couple with the stimulatory G protein, Gsa, and those that inhibit this second messenger couple with the inhibitory G protein, Gia, and these either stimulate or inhibit adenylyl cyclase, the effector enzyme responsible for synthesis of cAMP (Duman and Nestler 1999). There are at least nine different forms of adenylyl cyclase that have been identified by molecular cloning, each with a unique distribution in the brain. The different types of adenylyl cyclase are activated by Gsa as well as the diterpene forskolin, but are differentially regulated by Gia, the Py subunits, Ca, and by phosphorylation. This provides for fine control of adenylyl cyclase enzyme activity and regulation by other effector pathways. 

AC = stimulates adenylate cyclase activity -AC = inhibits forskolin-stimulated adenylate cyclase activity PI = stimulates phosphatidylinositol (PI) hydrolysis. 

De Vivo M, Maayani S. Characterization of the 5-hydroxytryptaminela receptor-mediated inhibition of forskolin-stimulated adenylate cyclase activity in guinea pig and rat hippocampal membranes. J Pharmacol Exp Ther 1986 238 248-253. 

Consistent with the sequence similarities between the ORLl and opioid receptors, activation of the ORLl receptor triggers the same signal transduction mechanisms as used by the opioid receptors. Thus activation of ORLl receptors inhibits both forskolin-stimulated adenylyl (yclase and currents and activates several other effectors, including inward rectifying channels, protein kinase C, mitogen-activated protein kinase (MAP kinase) and phospholipase C (see Ref 89 for a review). 

In functional experiments we studied whether or not the split chimeric M2-trunc/M 3-tail receptor retains in part the functional activity of the wild type M2 and M3 receptors. Carbachol stimulation of COS-7 cells co-transfected with the split chimeric M2-trunc/M 3-tail receptor neither inhibited forskolin-stimulated cAMP accumulation nor induced inositol monophosphate accumulation (Fig. 3a and b). It is important to note that carbachol stimulation of COS-7 cells co-transfected with fragments originating from the same receptor, M2-trunc/M2-tail and M3-trunc/M3-tail resulted respectively in the inhibition of adenylate... 

Note intrinsic Activity compared to the full DA agonist quinpirole inhibition of forskolin-stimulated cAMP accumulation in GH4C1 cells transfected with the DA D2 receptor. 

Inhibition of Forskolln-Stimulated Activation of Adenylate Cyclase -Inhibition of forskolin-stlmulated adenylate cyclase in membranes and cells has been observed with a2 80 l8ts In platelets, and adipocytes 36,64 muscarinic-cholinergic agonists In cardiac cells Aj -adenoslne agonists and insulin in rat adipocytes 35 somatostatin in S49 lymphoma cells29,66,67 pituitary and dopamine D2-agonists in pituitary.68 The Inhibition varies between 50 and 75%. 

Forskolin activation of adenylate cyclase can be inhibited by high concentrations of detergents and low molecular weight alcohols. Inhibition of forskolin stimulated adenylate cyclase by ethanol can be observed at 0.2M and results in 50% Inhibition at l.OM. Butanol and propanol are more effective at Inhibiting forskolin stimulated adenylate cyclase than ethanol. Dimethyl sulfoxide inhibits the stimulation of adenylate cyclase by forskolin much less than ethanol. 5... 

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