Cl−secretion in the colon can be activated by an increase of either intracellular Ca2+ or cAMP. In this study we examined a possible interdependence of the two second-messenger pathways in human colonic epithelium. When measured in a modified Ussing chamber, carbachol (CCH; 100 μmol/l, basolateral), via an increase in cytosolic Ca2+concentration ([Ca2+]i), activated a transient lumen-negative equivalent short-circuit current ( I sc) [change (Δ) in I sc = −79.4 ± 7.5 μA/cm2]. Previous studies indicated that intracellular Ca2+ directly acts on basolateral K+ channels, thus enhancing driving force for luminal Cl− exit. Increased intracellular cAMP (by basolateral addition of 100 μmol/l IBMX and 1 μmol/l forskolin) activated a sustained lumen-negative current (Δ I sc = −42.4 ± 7.2 μA/cm2) that was inhibited by basolateral trans-6-cyano-4-( N-ethylsulfonyl- N-methylamino)-3-hydroxy-2,2-dimethyl&2-chromane (10 μmol/l), a blocker of KvLQT1 channels. In the presence of elevated cAMP, the CCH-activated currents were augmented (Δ I sc = 167.7 ± 32.7 μA/cm2), suggesting cooperativity of the Ca2+- and cAMP-mediated responses. Inhibition of endogenous cAMP production by indomethacin (10 μmol/l) significantly reduced CCH-activated currents and even reversed the polarity in 70% of the experiments. The transient lumen-positive I sc was probably due to activation of apical K+channels because it was blocked by luminal Ba2+ (5 mmol/l) and tetraethylammonium (10 mmol/l). In the presence of indomethacin (10 μmol/l, basolateral), an increase of cAMP activated a sustained negative I sc. Under these conditions, CCH induced a large further increase in lumen-negative I sc(Δ I sc = −100.0 ± 21.0 μA/cm2). We conclude that CCH acting via [Ca2+]ican induce Cl− secretion only in the presence of cAMP, i.e., when luminal Cl− channels are already activated. The activation of a luminal and basolateral K+ conductance by CCH may be essential for transepithelial KCl secretion in human colon.
Acute liver failure (ALF) in infancy and childhood is a life-threatening emergency. Few conditions are known to cause recurrent acute liver failure (RALF), and in about 50% of cases, the underlying molecular cause remains unresolved. Exome sequencing in five unrelated individuals with fever-dependent RALF revealed biallelic mutations in NBAS. Subsequent Sanger sequencing of NBAS in 15 additional unrelated individuals with RALF or ALF identified compound heterozygous mutations in an additional six individuals from five families. Immunoblot analysis of mutant fibroblasts showed reduced protein levels of NBAS and its proposed interaction partner p31, both involved in retrograde transport between endoplasmic reticulum and Golgi. We recommend NBAS analysis in individuals with acute infantile liver failure, especially if triggered by fever.
Mutations in NBAS cause a complex disease with a wide clinical spectrum ranging from isolated RALF to a multisystemic phenotype. Thermal susceptibility of the syntaxin 18 complex is the basis of fever dependency of ALF episodes. NBAS deficiency is the first disease related to a primary defect of retrograde transport. Identification of NBAS deficiency allows optimized therapy of liver crises and even prevention of further episodes.
In children, the ratio of forced expiratory volume in 1 s (FEV1) to forced vital capacity (FVC) is reportedly constant or falls linearly with age, whereas the ratio of residual volume (RV) to total lung capacity (TLC) remains constant. This seems counter-intuitive given the changes in airway properties, body proportions, thoracic shape and respiratory muscle function that occur during growth. The age dependence of lung volumes, FEV1/FVC and RV/TLC were studied in children worldwide.Spirometric data were available for 22,412 healthy youths (51.4% male) aged 4-20 yrs from 15 centres, and RV and TLC data for 2,253 youths (56.7% male) from four centres; three sets included sitting height (SH). Data were fitted as a function of age, height and SH.In childhood, FVC outgrows TLC and FEV1, leading to falls in FEV1/FVC and RV/TLC; these trends are reversed in adolescence. Taking into account SH materially reduces differences in pulmonary function within and between ethnic groups. The highest FEV1/FVC ratios occur in those shortest for their age.When interpreting lung function test results, the changing pattern in FEV1/FVC and RV/TLC should be considered. Prediction equations for children and adolescents should take into account sex, height, age, ethnic group, and, ideally, also SH.
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