l-858051 and 1-9-dideoxyforskolin

The effects of increases in cellular adenosine 3'5'-cyclic monophosphate (cAMP) on 5-hydroxytryptamine-(5-HT-) induced generation of inositol phosphates (IPs) and increases in intracellular Ca2+ ([Ca2+]i) were investigated using canine cultured tracheal smooth muscle cells (TSMCs). Cholera toxin and forskolin induced concentration- and time-dependent cAMP formation with half-maximal effects (-logEC50) produced at concentrations of 7.0 +/- 0.5 and 4.9 +/- 0.4 respectively. Pretreatment of TSMCs with either forskolin or dibutyryl cAMP inhibited 5-HT-stimulated responses. Even after treatment for 24h, these agents still inhibited the 5-HT-induced Ca2+ mobilization. The inhibitory effects of these agents produced both depression of the maximal response and a shift to the right of the concentration response curves of 5-HT. The water-soluble forskolin analogue L-858051 [7-deacetyl-7beta-(gamma-N-methylpiperazino)-butyryl forskolin] significantly inhibited the 5-HT-stimulated accumulation of IPs. In contrast, the addition of 1,9-dideoxy forskolin, an inactive forskolin analogue, had little effect on this response. Moreover, SQ-22536 [9-(tetrahydro-2-furanyl)-9-H-purin-6-amine], an inhibitor of adenylate cyclase, and both H-89 [N-(2-aminoethyl)-5-isoquinolinesulphonamide] and HA-1004[N-(2-guanidinoethyl)-5-isoquinolinesulphonamide], inhibitors of cAMP-dependent protein kinase (PKA), attenuated the ability of forskolin to inhibit the 5-HT-stimulated accumulation of IPs. These results suggest that activation of cAMP/PKA was involved in these inhibitory effects of forskolin. The AlF4--induced accumulation of IPs was inhibited by forskolin, suggesting that G protein(s) are directly activated by AlF4-- and uncoupled from phospholipase C by forskolin treatment. These results suggest that activation of cAMP/PKA might inhibit the 5-HT-stimulated phosphoinositide breakdown and consequently reduce the [Ca2+]i increase or inhibit both responses independently.

Topics: Adenine; Aluminum Compounds; Animals; Bucladesine; Calcium; Cholera Toxin; Colforsin; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Diterpenes; Dogs; Dose-Response Relationship, Drug; Enzyme Inhibitors; Female; Fluorides; GTP-Binding Proteins; Isoquinolines; Male; Muscle, Smooth; PC12 Cells; Rats; Serotonin; Serotonin Antagonists; Sulfonamides; Trachea

Oligodendrocyte differentiation is accelerated by analogs of cyclic AMP (cAMP), such as N6,2-'O-dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP) or 8-bromo cAMP, in developing rat glial cell cultures (Raible and McMorris, 1989). However, it is not known whether the immature developing oligodendrocytes have G protein-coupled adenylate cyclase capable of generating cAMP, as would be required if development of the cells is normally regulated by endogenous cAMP. In the present study, we demonstrate that the diterpene forskolin, a potent activator of adenylate cyclase, or cholera toxin, which activates adenylate cyclase through G protein modification, can induce a precocious increase in oligodendrocyte number. When both forskolin and cholera toxin are added together, oligodendrocyte differentiation is induced to a level similar to that observed in response to cAMP analogs. These results establish for the first time that modulation of the endogenous cAMP regulatory system alters the schedule of oligodendrocyte differentiation.

Topics: Adenylyl Cyclases; Animals; Bucladesine; Cell Differentiation; Cells, Cultured; Cerebral Cortex; Cholera Toxin; Colforsin; Cyclic AMP; Diterpenes; Enzyme Induction; Oligodendroglia; Rats; Second Messenger Systems; Stimulation, Chemical

Forskolin and four analogues of forskolin, 7-beta-[gamma-(N'-methylpiperazino)-butyryloxy]-7-desacet ylforskolin, 7-desacetylforskolin, 7-tosyl-7-desacetylforskolin, and 1,9-dideoxyforskolin, were tested for their ability to activate adenylate cyclase, inhibit glucose transport, and inhibit cytochalasin B binding in rat adipocyte membranes. Forskolin was the most potent analogue in activating adenylate cyclase with an EC50 of 2 microM, whereas 7-beta-[gamma-(N'-methylpiperazino)butyryloxy]-7-desacety lforskolin and 7-desacetylforskolin were less potent, with EC50 values of 3 microM and 20 microM, respectively. The 7-tosyl-7-desacetylforskolin and 1,9-dideoxyforskolin did not stimulate adenylate cyclase even at the highest concentrations tested (100 microM). In contrast, forskolin and all of the analogues were able to fully inhibit glucose transport in adipocyte plasma membranes. The order of potency for the inhibition was forskolin greater than 7-beta-[gamma-(N'-methylpiperazino)butyryloxy]-7-desacety lforskolin greater than 7-desacetylforskolin greater than 7-tosyl-7-desacetylforskolin greater than 1,9-dideoxyforskolin, and the EC50 values were 0.24 microM, 1.8 microM, 7.1 microM, 8.8 microM, and 12.8 microM, respectively. Cytochalasin B binding to rat adipocyte membranes was inhibited by forskolin and the four analogues with the same order of potency as observed for the inhibition of glucose transport. Thus, the site of action of forskolin which is responsible for the inhibition of glucose transport and cytochasin B binding exhibits structural requirements for forskolin and its analogues that are different from those of the site responsible for the activation of adenylate cyclase.

Topics: Adenylyl Cyclases; Adipose Tissue; Animals; Biological Transport, Active; Colforsin; Cytochalasin B; Diterpenes; Enzyme Activation; Glucose; Male; Rats