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This Article Full Text Full Text (PDF) Supplemental Figures All Versions of this Article: 295/4/L708    most recent 00536.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Garcia-Verdugo, I. Articles by Haller, T. PubMed PubMed Citation Articles by Garcia-Verdugo, I. Articles by Haller, T.

Long-term exposure to LPS enhances the rate of stimulated exocytosis and surfactant secretion in alveolar type II cells and upregulates P2Y₂ receptor expression

¹Institut de Biochimie et Biophysique Moléculaire et Cellulaire, University of Paris-Sud, Orsay, France; ²Department of Physiology, Innsbruck Medical University, Innsbruck, Austria; and ³Institute of General Physiology, University of Ulm, Ulm, Germany

Submitted 28 December 2007 ; accepted in final form 3 August 2008

Bacterial LPS is a potent proinflammatory molecule. In the lungs, LPS induces alterations in surfactant pool sizes and phospholipid (PL) contents, although direct actions of LPS on the alveolar type II cells (AT II) are not yet clear. For this reason, we studied short- and long-term effects of LPS on basal and agonist-stimulated secretory responses of rat AT II by using Ca²⁺ microfluorimetry, a microtiter plate-based exocytosis assay, by quantitating PL and ³H-labeled choline released into cell supernatants and by using quantitative PCR and Western blot analysis. Long term, but not short term, exposures to LPS led to prolonged ATP-induced Ca²⁺ signals and an increased rate in vesicle fusions with an augmented release of surfactant PL. Most notably, the stimulatory effect of LPS was ATP-dependent and may be mediated by the upregulation of the purinergic receptor subtype P2Y₂. Western blot analysis confirmed higher levels of P2Y₂, and suramin, a P2Y receptor antagonist, was more effective in LPS-treated cells. From these observations, we conclude that LPS, probably via Toll-like receptor-4, induces a time-dependent increase in P2Y₂ receptors, which, by yet unknown mechanisms, leads to prolonged agonist-induced Ca²⁺ responses that trigger a higher activity in vesicle fusion and secretion. We further conclude that chronic exposure to endotoxin sensitizes AT II to increase the extracellular surfactant pool, which aids in the pulmonary host defense mechanisms.

endotoxin; lipopolysaccharide; lung; P2Y₂