Effect of Oxygen Exposure on ATP Content of Rat Bronchoalveolar Lavage

Abstract

ABSTRACT. Exogenous ATP stimulates surfactant phospholipid secretion in vitro through binding to P2-purinoceptors on the surface of the alveolar type I1 cell. To determine whether ATP is present in the bronchoalveolar space at concentrations sufficient to stimulate phospholipid secretion, we determined bronchoalveolar lavage ATP content in rats exposed to different inspired oxygen concentrations. Bronchoalveolar lavage ATP content of control animals exposed to room air was 155 + 12 nmol ATPIlavage Alveolar type I1 cells synthesize and secrete surfactant phospholipids in response to a variety of secretagogues which include P-adrenoceptor agonists (I), phorbol esters (2), calcium ionophores (3), and cytochalasins (4). One of the most potent agonists for surfactant phospholipid secretion in vitro is exogenous ATP, which activates cell surface Pz-purinoceptors mobilizing intracellular calcium in association with surfactant phospholipid secretion (5, 6). Whether ATP is present in relevant concentrations in the airway and whether ATP plays a similar role in vivo is unknown. We therefore undertook the present study to determine whether ATP is present in bronchoalveolar lavage in concentrations sufficient to mediate surfactant phospholipid secretion in vivo. Exposure to hyperoxia affects metabolism and airway content of the major surfactant-associated protein and DSPC. However, specific effects vary depending on animal species, age, and level and duration of inspired oxygen. Young et ul. (7) found increased lavage and lung DSPC content in adult rats exposed to 85% oxygen for 7 d. Nogee and Wisp6 (8) reported increased airway content of DSPC in adult rats exposed to 85% oxygen for 3 or 7 d. This increase was associated with increased synthesis and secretion of the major surfactant-associated protein SP-A. In contrast, Ward and Roberts (9) reported decreased synthesis and secretion of DSPC by lung slices obtained from newborn rabbits exposed to 95% oxygen for 48 h. Thus, hyperoxia causes a significant perturbation of surfactant homeostasis. As ATP is a potent stimulus for surfactant phospholipid secretion in vitro (5, 6) and hyperoxia has also been reported to modulate surfactant phospholipid secretion (7, 8), we tested whether changes in bronchoalveolar lavage ATP content are associated with hyperoxia-induced changes in DSPC secretion by measuring bronchoalveolar lavage ATP and disaturated phosphatidylcholine content in rats exposed to varying inspired oxygen concentrations. MATERIALS AND METHODS Materials.Male rats ( 1 50-250 g) were obtained from Charles River Breeding Laboratories, Inc., Wilmington, MA. ATP, ADP, AMP (all as sodium salts), adenosine, NADP, glucose-6-phosphate dehydrogenase, hexokinase, and tetrabutyl ammonium hydrogen sulfate were obtained from Sigma Chemical Co., St. Louis, MO.Methods. Adult male Sprague-Dawley rats were exposed to hyperoxia or room air for the dose-response study. The average wt of the study animals was 350 g for the dose-response study, and 250 g for the time course. The oxygen-tre...

P2Y2 receptor‐mediated inhibition of ion transport in distal lung epithelial cells

“…Schwiebert et al ., 1995; Taylor et al ., 1998; Schwiebert, 1999). Interestingly, ATP has been detected in rat bronchiolar/alveolar lavage fluid and the inferred concentration in the distal airway surface liquid appears high enough to activate the receptors described in the present study (Rice et al ., 1989). These nucleotides may therefore exert tonic control over both surfactant secretion and ion transport.…”

Interfacial stress affects rat alveolar type II cell signaling and gene expression

“…ATP is released by AT II cells in response to stretch and interacts with purinergic P2Y 2 and P2X 4 receptors to increase [Ca 2ϩ ] i (46,49). Within the alveolar lining fluid, ATP might reach millimolar concentrations (58), but the source of it is essentially unknown. Beside a supposed release from scattered purinergic nerve terminals, and release due to cell membrane stress failures, a channel-gated release from AT II cells, as well as a mechanosensitive ATP-exocytosis, has been proposed (16,55).…”

Coupling of airway ciliary activity and mucin secretion to mechanical stresses by purinergic signaling

“…ATP and other nucleotides have been measured in liquids perfused over nasal turbinates (Donaldson et al 2000) and recovered bronchoalveolar lavage liquids (Rice et al 1989;Rich et al 2003;Douillet et al 2005;Esther et al 2008), implying release from airway epithelial surfaces. More direct evidence for nucleotide release from the airway epithelium has come from in vitro studies using HBE cell cultures (Grygorczyk 1997;Watt et al 1998;Donaldson et al 2000;Homolya et al 2000;Lazarowski et al 2004;Okada et al 2006; and see below).…”