Chronic regulation of colonic epithelial secretory function by activation of G protein-coupled receptors.

BACKGROUND: Enteric neurotransmitters that act at G protein-coupled receptors (GPCRs) are well known to acutely promote epithelial Cl(-) and fluid secretion. Here we examined if acute GPCR activation might have more long-term consequences for epithelial secretory function. METHODS: Cl(-) secretion was measured as changes in short-circuit current across voltage-clamped T(84) colonic epithelial cells. Protein expression was measured by western blotting and intracellular Ca(2+) levels by Fura-2 fluorescence. KEY RESULTS: While acute (15 min) treatment of T(84) cells with a cholinergic G(q) PCR agonist, carbachol (CCh), rapidly stimulated Cl(-) secretion, subsequent CCh-induced responses were attenuated in a biphasic manner. The first phase was transient and resolved within 6 h but this was followed by a chronic phase of attenuated responsiveness that was sustained up to 48 h. CCh-pretreatment did not chronically alter responses to another G(q)PCR agonist, histamine, or to thapsigargin or forskolin which elevate intracellular Ca(2+) and cAMP, respectively. This chronically acting antisecretory mechanism is not shared by neurotransmitters that activate G(s)PCRs. Conditioned medium from CCh-pretreated cells mimicked its chronic antisecretory actions, suggesting involvement of an epithelial-derived soluble factor but further experimentation ruled out the involvement of epidermal growth factor receptor ligands. Acute CCh exposure did not chronically alter surface expression of muscarinic M(3) receptors but inhibited intracellular Ca(2+) mobilization upon subsequent agonist challenge. CONCLUSIONS \u26 INFERENCES: These data reveal a novel, chronically acting, antisecretory mechanism that downregulates epithelial secretory capacity upon repeated G(q)PCR agonist exposure. This mechanism involves release of a soluble factor that uncouples receptor activation from downstream prosecretory signals

Quantitative nuclear magnetic resonance imaging detects subclinical changes over 1 year in skeletal muscle of GNE myopathy.

BACKGROUND AND OBJECTIVE: To identify the most responsive and sensitive clinical outcome measures in GNE myopathy. METHODS: ClinBio-GNE is a natural history study in GNE myopathy. Patients were assessed prospectively by clinical, functional and quantitative nuclear magnetic resonance imaging (qNMRI) evaluations. Strength and functional tests included Myogrip, Myopinch, MoviPlate and Brooke assessments for upper limb and the 6-min walk distance for lower limb. qNMRI was performed for determining the degree of fatty infiltration and trophicity in leg, thigh, forearm and hand skeletal muscles. Ten GNE myopathy patients were included. Three patients were non-ambulant. Age and gender-matched healthy subjects were used as controls. RESULTS: Fatty infiltration and contractile cross-sectional area changed inversely and significantly in lower distal limbs and in proximal lower and distal upper limbs over 1 year. qNMRI indices and functional assessment results were strongly correlated. CONCLUSIONS: Even in a limited number of patients, qNMRI could detect a significant change over a 1-year period in GNE myopathy, which suggests that qNMRI could constitute a surrogate endpoint in this slowly progressive disease. Quantitative NMRI outcome measures can monitor intramuscular fat accumulation with high responsiveness. Longer follow-up should improve our understanding of GNE myopathy evolution and also lead to the identification of non-invasive outcome measures with the highest discriminant power for upcoming clinical trials