RESUMO
Trichinella spiralis infection causes hyperexcitability in enteric after-hyperpolarising (AH) sensory neurons that is mimicked by neural, immune or inflammatory mediators known to stimulate adenylyl cyclase (AC)/cyclic 3',5'-adenosine monophosphate (cAMP) signaling. The hypothesis was tested that ongoing modulation and sustained amplification in the AC/cAMP/phosphorylated cAMP related element binding protrein (pCREB) signaling pathway contributes to hyperexcitability and neuronal plasticity in gut sensory neurons after nematode infection. Electrophysiological, immunological, molecular biological or immunochemical studies were done in T. spiralis-infected guinea-pigs (8000 larvae or saline) after acute-inflammation (7 days) or 35 days p.i., after intestinal clearance. Acute-inflammation caused AH-cell hyperexcitability and elevated mucosal and neural tissue levels of myeloperoxidase, mast cell tryptase, prostaglandin E2, leukotrine B4, lipid peroxidation, nitric oxide and gelatinase; lower level inflammation persisted 35 days p.i. Acute exposure to blockers of AC, histamine, cyclooxygenase or leukotriene pathways suppressed AH-cell hyperexcitability in a reversible manner. Basal cAMP responses or those evoked by forskolin (FSK), Ro-20-1724, histamine or substance P in isolated myenteric ganglia were augmented after T. spiralis infection; up-regulation also occurred in AC expression and AC-immunoreactivity in calbindin (AH) neurons. The cAMP-dependent slow excitatory synaptic transmission-like responses to histamine (mast cell mediator) or substance P (neurotransmitter) acting via G-protein coupled receptors (GPCR) in AH neurons were augmented by up to 2.5-fold after T. spiralis infection. FSK, histamine, substance P or T. spiralis acute infection caused a 5- to 30-fold increase in cAMP-dependent nuclear CREB phosphorylation in isolated ganglia or calbindin (AH) neurons. AC and CREB phosphorylation remained elevated 35 days p.i.. Ongoing immune activation, AC up-regulation, enhanced phosphodiesterase IV activity and facilitation of the GPCR-AC/cAMP/pCREB signaling pathway contributes to T. spiralis-induced neuronal plasticity and AH-cell hyperexcitability. This may be relevant in gut nematode infections and inflammatory bowel diseases, and is a potential therapeutic target.
Assuntos
AMP Cíclico/metabolismo , Mucosa Intestinal/inervação , Plasticidade Neuronal/fisiologia , Neurônios Aferentes/fisiologia , Trichinella spiralis/fisiologia , Triquinelose/metabolismo , Animais , Colforsina/farmacologia , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Didesoxiadenosina/análogos & derivados , Didesoxiadenosina/farmacologia , Dinoprostona/metabolismo , Cobaias , Histamina/farmacologia , Imidazóis/farmacologia , Técnicas In Vitro , Mucosa Intestinal/efeitos dos fármacos , Leucotrieno B4/metabolismo , Lisina/análogos & derivados , Lisina/farmacologia , Masculino , Potenciais da Membrana/fisiologia , Músculo Liso/efeitos dos fármacos , Músculo Liso/inervação , Plasticidade Neuronal/efeitos dos fármacos , Neurônios Aferentes/efeitos dos fármacos , Neurônios Aferentes/metabolismo , Neurônios Aferentes/parasitologia , Óxido Nítrico/metabolismo , Peroxidase/metabolismo , Transdução de Sinais , Substância P/farmacologia , Substâncias Reativas com Ácido Tiobarbitúrico/metabolismo , Trichinella spiralis/metabolismo , Triquinelose/parasitologia , Triptases/metabolismoRESUMO
BACKGROUND & AIMS: The aim was to determine whether adenosine receptors modulate cAMP, intracellular free calcium ([Ca(2+)](i)), and 5-hydroxytryptamine (5-HT) release in human carcinoid BON cells. METHODS: Adenosine receptor (R) mRNA, proteins, and function were identified by Western blots, immunofluorescent labeling, Fluo-4/AM [Ca(2+)](i) imaging, and pharmacologic/physiologic techniques. RESULTS: A1, A2, and A3Rs were present in BON cells and carcinoid tumors. Baseline 5-HT levels increased with adenosine deaminase, activation of A2Rs, and inhibition of A3Rs, whereas A3R activation decreased 5-HT. A2R antagonists or blockade of adenosine reuptake that elevates extracellular adenosine reduced mechanically evoked 5-HT release. In single BON cells, touch elevated [Ca(2+)](i) responses were augmented by adenosine deaminase, A1, and A3R antagonists. CONCLUSIONS: Tonic or mechanically evoked release of endogenous adenosine is a critical determinant of differential activation of adenosine receptors and may have important implications for gut mechanosensory reflexes.