Agents that stimulate phosphoinositide turnover also elevate cAMP in SK-N-SH human neuroblastoma cells

Interleukin-13 inhibits protein kinase C-triggered respiratory burst in human monocytes. Role of calcium and cyclic AMP

Interleukin-13 (IL-13), a novel cytokine produced by activated lymphocytes modulates some monocyte functions, but no data is available concerning the signal transduction pathway. We show here, the inhibitory effect of IL-13 on 12-O-tetradecanoylphorbol-13-acetate (TPA)-triggered reactive oxygen intermediate production in human monocytes and the signals involved in this response. Our results show that IL-13 produces rapid and transient phosphoinositide hydrolysis and intracellular Ca2+ mobilization. Furthermore, IL-13 induces intracellular cAMP accumulation through inositol 1,4,5-trisphosphate-dependent Ca2+ mobilization. Metabolic inhibitors were used to relate the first steps in signaling pathways to the inhibitory effect of IL-13 on TPA-triggered reactive oxygen intermediate production. Indeed, inhibitors of phospholipase C (neomycin), intracellular Ca2+ mobilization (8-[N,N-diethylamino]-octyl 3,4,5-trimethoxybenzoate hydrochloride), adenylate cyclase (delta 9-tetrahydrocannabinol), and protein kinase A (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) impair the IL-13 inhibitory response. Altogether these observations indicate that modulatory effect of IL-13 on the TPA-induced oxidative burst is the result of the intracellular cAMP accumulation through an inositol 1,4,5-trisphosphate-induced Ca2+ mobilization-dependent pathway.

Antagonism by (R)- and (S)-trihexyphenidyl of muscarinic stimulation of adenylyl cyclase in rat olfactory bulb and inhibition in striatum and heart

1. Activation of muscarinic receptors in rat olfactory bulb stimulates adenylyl cyclase activity. This response was competitively antagonized by the (R)- and (S)-enantiomers of trihexyphenidyl with pA2 values of 8.84 and 6.09, respectively. 2. Similarly, in rat striatal homogenates, muscarinic inhibition of adenylyl cyclase activity was antagonized by the (R)- and (S)-enantiomers with pA2 values of 8.75 and 6.12, respectively. 3. In contrast, in rat myocardium the muscarinic inhibition of the adenosine 3':5'-cyclic monophosphate (cyclic AMP) formation was more weakly antagonized by trihexyphenidyl, with a particularly marked loss (15 fold) in activity of the (R)-enantiomer. The (R)- and (S)-enantiomers had pA2 values of 7.64 and 5.72, respectively. 4. Each muscarinic response was completely antagonized by increasing concentrations of (R)-trihexyphenidyl with a Hill coefficient not significantly different from unity. 5. The present study shows that the muscarinic receptors coupled to stimulation of adenylyl cyclase in the olfactory bulb display high stereoselectivity for the enantiomers of trihexyphenidyl. The affinities of these receptors for the antagonists are similar to those shown by the striatal receptors. This finding supports the hypothesis that both the muscarinic stimulation of adenylyl cyclase in the olfactory bulb and the muscarinic inhibition of the enzyme in striatum are mediated by activation of a receptor subtype pharmacologically equivalent to the m4 gene product. On the other hand, the weaker affinities and the lower stereoselectivity for the trihexyphenidyl enantiomers exhibited by the muscarinic inhibition of adenylyl cyclase in the heart are consistent with the involvement of M2 receptors in this response.

Muscarinic receptor-mediated increase in zeta-PKC expression in SK-N-SH human neuroblastoma cells

Anti-peptide antibodies specific for each protein kinase C (PKC) isozyme were used to screen SK-N-SH human neuroblastoma cells. These cells were found to express only alpha- and zeta-PKC. Stimulation of these cells with phorbol esters caused alpha- but not zeta-PKC to translocate from cytosolic to membrane fractions. Stimulation of these cells with carbachol, which releases inositol trisphosphate and diacylglycerol, caused a transient translocation of alpha-PKC but not of zeta-PKC. Carbachol did, however, cause a gradual increase in immunoreactive zeta-PKC which reached maximal values 10-20 min after stimulation. These results implicate zeta-PKC in a receptor-mediated signalling event.