h-89 and 8-bromoadenosine-3--5--cyclic-monophosphorothioate

We have explored the mechanisms involved in the facilitation of glutamate release mediated by the activation of kainate receptors (KARs) in the cortex using isolated nerve terminals (synaptosomes). Kainate (KA) produced an increase on glutamate release at 100 μM. The effect of KA was antagonized by NBQX (with AMPA receptors blocked by GYKI53655). This facilitation was suppressed by the inhibition of PKA activation by Rp-Br-cAMP and H-89. Moreover, the facilitation of glutamate release mediated by KAR requires the mobilization of intrasynaptosomal Ca(2+) stores and the formation of a Ca(2+)-calmodulin complex. We conclude that KARs present on presynaptic terminals in the neocortex mediate the facilitation of glutamate release through a mechanism involving an increase in cytosolic Ca(2+) to activate a Ca(2+)-calmodulin-AC/cAMP/PKA signaling cascade.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; Benzodiazepines; Calcium; Calmodulin; Cerebral Cortex; Cyclic AMP-Dependent Protein Kinases; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Glutamic Acid; Isoquinolines; Kainic Acid; Male; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, Kainic Acid; Receptors, Presynaptic; Sulfonamides; Synaptic Transmission; Synaptosomes; Thionucleotides

We used intracellular recording to investigate the functional interaction between protein kinase C (PKC) and protein kinase A (PKA) signal transduction cascades in the control of transmitter release in the neuromuscular synapses from adult rats. Our results indicate that: 1) PKA and PKC are independently involved in asynchronous release. 2) Evoked acetylcholine (ACh) release is enhanced with the PKA agonist Sp-8-BrcAMP and the PKC agonist phorbol ester (PMA). 3) PKA has a constitutive role in promoting a component of normal evoked transmitter release because, when the kinase is inhibited with H-89, the release diminishes. However, the PKC inhibitor calphostin C (CaC) does not affect ACh release. 4) PKA regulates neurotransmission without PKC involvement because, after PMA or CaC modulation of the PKC activity, coupling to the ACh release of PKA can normally be stimulated with Sp-8-BrcAMP or inhibited with H-89. 5) After PKA inhibition with H-89, PKC stimulation with PMA (or inhibition with CaC) does not lead to any change in evoked ACh release. However, in PKA-stimulated preparations with Sp-8-BrcAMP, PKC becomes tonically active, thus potentiating a component of release that can now be blocked with CaC. In normal conditions, therefore, PKA was able to modulate ACh release independently of PKC activity, whereas PKA stimulation caused the PKC coupling to evoked release. In contrast, PKA inhibition prevent PKC stimulation (with the phorbol ester) and coupling to ACh output. There was therefore some dependence of PKC on PKA activity in the fine control of the neuromuscular synaptic functionalism and ACh release.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Acetylcholine; Analysis of Variance; Animals; Cyclic AMP-Dependent Protein Kinases; Isoquinolines; Membrane Potentials; Naphthalenes; Neuromuscular Junction; Protein Kinase C; Protein Kinase Inhibitors; Rats; Rats, Sprague-Dawley; Signal Transduction; Sulfonamides; Tetradecanoylphorbol Acetate; Thionucleotides

Airway ciliary beat frequency regulation is complex but in part influenced by cyclic adenosine monophosphate (cAMP)-mediated changes in cAMP-dependent kinase activity, yet the cAMP concentration required for increases in ciliary beat frequency and the temporal relationship between ciliary beat frequency and cAMP changes are unknown. A lentiviral gene transfer system was developed to express a fluorescence resonance energy transfer (FRET)-based cAMP sensor in ciliated cells. Expression of fluorescently tagged cAMP-dependent kinase subunits from the ciliated-cell-specific foxj1 promoter enhanced expression in fully differentiated ciliated human airway epithelial cells, and permitted simultaneous measurements of ciliary beat frequency and cAMP (represented by the FRET ratio). Apical application of forskolin (1 microM, 10 microM, 20 microM) and, in permeabilized cells, basolateral cAMP (20 microM, 50 microM, 100 microM) caused dose-dependent, albeit similar and simultaneous-increases in cAMP and ciliary beat frequency. However, decreases in cAMP preceded decreases in ciliary beat frequency, suggesting that either cellular cAMP decreases before ciliary cAMP or the dephosphorylation of target proteins by phosphatases occur at a rate slower than the rate of cAMP hydrolysis.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Cell Line, Tumor; Cell Movement; Cilia; Colforsin; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Dose-Response Relationship, Drug; Epithelial Cells; Fluorescence Resonance Energy Transfer; Forkhead Transcription Factors; Humans; Immunohistochemistry; Isoquinolines; Kinetics; Luminescent Proteins; Lung; Phosphorylation; Promoter Regions, Genetic; Protein Binding; Protein Subunits; Recombinant Fusion Proteins; Sulfonamides; Thionucleotides; Time Factors

This study determined whether the alpha4 subunit of human alpha4beta2 neuronal nicotinic receptors is phosphorylated in situ by cyclic AMP-dependent protein kinase (PKA) or protein kinase C (PKC). To accomplish this, human cloned epithelial cells stably transfected with the human alpha4beta2 nicotinic receptor (SH-EP1-halpha4beta2) were incubated with 32P-orthophosphate to label endogenous ATP stores, and the phosphorylation of alpha4 subunits was determined in the absence or presence of PKA or PKC activation. Autoradiographs and immunoblots indicated that alpha4 subunits immunoprecipitated from a membrane preparation of SH-EP1-halpha4beta2 cells exhibited a single 32P-labeled band corresponding to the alpha4 subunit protein; no signals were associated with untransfected SH-EP1 cells. The alpha4 subunits from SH-EP1-halpha4beta2 cells incubated in the absence of the activators exhibited a basal level of phosphorylation that was decreased in the presence of the PKA inhibitor H-89 (5 microM), but unaltered in the presence of the PKC inhibitor Ro-31-8220 (0.1 microM). Activation of PKA by forskolin (10 microM), dibutyryl-cAMP (1 mM), or Sp-8-Br-cAMP (1 mM) enhanced phosphorylation nearly threefold; the inactive isomer, Rp-8-Br-cAMP (1 mM) had no effect. In addition, the forskolin effect was totally blocked by the PKA inhibitor H-89 (5 microM). Activation of PKC by the phorbol esters PDBu (200 nM) or PMA (200 nM) increased alpha4 subunit phosphorylation approximately twofold, and the PDBu effect was blocked by the selective PKC inhibitor Ro-31-8220 (0.1 microM). These findings indicate that the alpha4 subunit of human alpha4beta2 nicotinic receptors is phosphorylated in situ by PKA and PKC.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Bucladesine; Carcinogens; Cell Line; Colforsin; Cyclic AMP-Dependent Protein Kinases; Enzyme Inhibitors; Humans; Indoles; Isoquinolines; Neurons; Phosphorylation; Protein Kinase C; Receptors, Nicotinic; Sulfonamides; Tetradecanoylphorbol Acetate; Thionucleotides; Transfection

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; Cell Line; Cricetinae; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Enzyme Inhibitors; Insulin; Islets of Langerhans; Isoquinolines; Neuropeptides; Pituitary Adenylate Cyclase-Activating Polypeptide; Sulfonamides; Thionucleotides