CAMP Analogs

In GH cells SST inhibits prolactin secretion induced by cAMP analogs and K+-induced depolarization in addition to inhibiting adenylyl cyclase activity [192], Similar data were also obtained with ACTH-secreting AtT-20 cells [203]. PTX blocks SST inhibition of ligand-induced and cAMP analog-induced secretions in both GH and AtT-20 cells [106,107]. Thus, it is clear that a G protein is involved in both the cAMP dependent and the cAMP-independent actions of SST. Quin-2 measurements showed that exposure of cells to SST lowers the intracellular Ca2+ levels. This effect is also PTX-sensitive [211-213], The decline in intracellular Ca2+ was concluded to be secondary to SST hyperpolarizing the cells by increasing K+ conductance [214,215]. Acetylcholine, like SST, causes inhibition of adenylyl cyclase, hy-... 

To validate interaction assays, a suitable biological model system is helpful. cAMP-dependent protein kinase (PKA) is used as such a model system in the assays described below. PKA is the main target for the second messenger cAMP in eukaryotic cells and, since it has been implicated in various human diseases, the development of cAMP analogs modulating PKA activity has provoked increasing interest. 

This information is a prerequisite for the development of cAMP analogs capable of permeating the cell membrane while maintaining their ability to bind to the regulatory subunit with high affinity. 

Reichel. V.. Masereeuw, R., van den Heuvel, J.f.M.W, Miller, D.S., and Pricker, G. (2007) Transport of a fluorescent cAMP analog in teleost proximal tubules. The American Journal of Physiology, 29 i, R2382—R2389,... 

Occludin phosphorylation may provide a molecular mechanism to control barrier properties. Studies from our group have demonstrated that both VEGF and shear stress induce permeability across endothelial monolayers associated with a rapid phosphorylation of occludin (67,68). The occludin phosphorylation was attenuated by a non-hydrolyzable cAMP analog that also inhibits shear-induced permeability (68). This phosphorylation of occludin appears to be serine or threonine directed since immunoprecipitation of occludin and phosphotyrosine blotting did not reveal any evidence of occludin tyrosine phosphorylation in this cell system (unpublished observation). However, in epithelial cells, evidence of occludin tyrosine phosphorylation exists (69). In addition, others have identified occludin phosphorylation in response to histamine (70) and use of brain extracts has helped identify casein kinase II as an occludin kinase (71). Collectively, this work demonstrates a close association of occludin phosphorylation with permeability. Future studies identifying specific occludin phosphorylation sites, followed by mutational analysis, should reveal the functional significance of occludin phosphorylation. 

Rydel, R.E. and Greene, L.A. (1988) cAMP analogs promote survival and neurite outgrowth in cultures of rat sympathetic and sensory neurons independently of nerve growth factor. Proc. Natl. Acad. Sci. USA 85 1257-1261. 

Relative Binding Affinities for cAMP Analogs in Phosphate Buffer (See Note 2)... 

To determine the relative affinity of the cell surface cAMP receptors for a cAMP analog, follow steps 1-4 of Subheading 3.2. 

A semilog plot of analog concentration (X-axis) vs. bound dpm (T-axis) can be used to determine relative affinity for a cAMP analog. 

The resistance to deacylatlon exhibited by intact adipocytesis not completely explainable. The need for further studies to delineate the catabolism of these and other cAMP analogs in a variety of tissues is obvious. 

Exposure of retinoic acid-treated F9 cells to dibutyryl cAMP results in the appearance of a stable new phenotype resembling parietal endoderm (Strickland et al., 1980 Kuff and Fewell, 1980 Rizzino and Crowley, 1980). The order of addition of the retinoic acid and the cAMP analog is critical treatment of cells with dibutyryl cAMP alone had no effect, and treatment of cells with dibutyryl cAMP followed by retinoic acid yielded a phenotype similar to that resulting from treatment with retinoic acid alone (Strickland et al., 1980). Thus it can be... 

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