Glutamine metabolism stimulates intestinal cell MAPKs by a cAMP-inhibitable, RAF-independent mechanism

AbstractBackground & Aims: Infectious diarrhea caused by viruses plus enterotoxigenic bacteria is often more severe than diarrhea induced by either pathogen alone. We postulated that the increased cell adenosine 3',5'-cyclic monophosphate (cAMP) concentration observed during infection by enterotoxigenic organisms retards the intestinal repair process by blocking activation of mitogen-activated protein kinases (MAPKs) in proliferating intestinal cells. Methods: We evaluated the effects of glutamine on MAPK activity, thymidine incorporation, and cell number in glutamine-starved and -sufficient rat intestinal crypt cells (IEC-6). Results: In glutamine-starved cells, 10 mmol/L glutamine in the absence of serum stimulated [3H]thymidine incorporation 8-fold. This effect was inhibited by 60% with 8-(4-chlorophenylthio) (8-CPT)-cAMP (100 μmol/L) + isobutyl methylxanthine (100 μmol/L). In cells not starved of glutamine, glutamine stimulated thymidine incorporation by 3-fold, and 8-CPT-cAMP completely blocked the mitogenic effect. Inhibition of proliferation by cAMP persisted for at least 68 hours after cAMP removal. In vitro kinase assays showed that glutamine signaling requires an intact ERK (extracellular signal–related kinase) pathway in unstarved cells. In starved cells, at least one other pathway (JNK) was activated by glutamine, and the mitogenic inhibition by 8-CPT-cAMP was incomplete. Other intestinal fuels (glucose and acetate) were not mitogenic. Conclusions: Increased levels of intracellular cAMP inhibit ERKs but only partially reduce glutamine-stimulated proliferation in enterocytes adapted to low glutamine.GASTROENTEROLOGY 2000;118:90-10

Studies on the equilibration of mercury vapor with blood /

"UR-582 ; Biology and Medicine ; TID-4500, (15th ed.).""Contract W-7401-eng-49 between the U.S. Atomic Energy Commission and the University of Rochester, administered by the Department of Radiation Biology of the School of Medicine and Dentistry.""Date completed: 11/23/60 ; Date of Issue: 1/6/61."Includes bibliographical references (pages 63-64).Mode of access: Internet

A mouse model for the renal salt-wasting syndrome pseudohypoaldosteronism

Aldosterone-dependent epithelial sodium transport in the distal nephron is mediated by the absorption of sodium through the highly selective, amiloride-sensitive epithelial sodium channel (ENaC) made of three homologous subunits (α, β, and γ). In human, autosomal recessive mutations of α, β, or γENaC subunits cause pseudohypoaldosteronism type 1 (PHA-1), a renal salt-wasting syndrome characterized by severe hypovolemia, high plasma aldosterone, hyponatremia, life-threatening hyperkaliemia, and metabolic acidosis. In the mouse, inactivation of αENaC results in failure to clear fetal lung liquid at birth and in early neonatal death, preventing the observation of a PHA-1 renal phenotype. Transgenic expression of αENaC driven by a cytomegalovirus promoter in αENaC(−/−) knockout mice [αENaC(−/−)Tg] rescued the perinatal lethal pulmonary phenotype and partially restored Na(+) transport in renal, colonic, and pulmonary epithelia. At days 5–9, however, αENaC(−/−)Tg mice showed clinical features of severe PHA-1 with metabolic acidosis, urinary salt-wasting, growth retardation, and 50% mortality. Adult αENaC(−/−)Tg survivors exhibited a compensated PHA-1 with normal acid/base and electrolyte values but 6-fold elevation of plasma aldosterone compared with wild-type littermate controls. We conclude that partial restoration of ENaC-mediated Na(+) absorption in this transgenic mouse results in a mouse model for PHA-1

Salt restriction induces pseudohypoaldosteronism type 1 in mice expressing low levels of the β-subunit of the amiloride-sensitive epithelial sodium channel

The amiloride-sensitive epithelial sodium channel (ENaC) is a heteromultimer of three homologous subunits (α-, β-, and γ-subunits). To study the role of the β-subunit in vivo, we analyzed mice in which the βENaC gene locus was disrupted. These mice showed low levels of βENaC mRNA expression in kidney (≈1%), lung (≈1%), and colon (≈4%). In homozygous mutant βENaC mice, no βENaC protein could be detected with immunofluorescent staining. At birth, there was a small delay in lung-liquid clearance that paralleled diminished amiloride-sensitive Na(+) absorption in tracheal explants. With normal salt intake, these mice showed a normal growth rate. However, in vivo, adult βENaC m/m mice exhibited a significantly reduced ENaC activity in colon and elevated plasma aldosterone levels, suggesting hypovolemia and pseudohypoaldosteronism type 1. This phenotype was clinically silent, as βENaC m/m mice showed no weight loss, normal plasma Na(+) and K(+) concentrations, normal blood pressure, and a compensated metabolic acidosis. On low-salt diets, βENaC-mutant mice developed clinical symptoms of an acute pseudohypoaldosteronism type 1 (weight loss, hyperkalemia, and decreased blood pressure), indicating that βENaC is required for Na(+) conservation during salt deprivation