The adenylate cyclase-coupled atp receptor and surfactant secretion in type ii pneumocytes from newborn rats. Gobran, Laurice I, and Seamus A. Rooney. Division of Perinatal Medicine, Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut 06510
APStracts 3:0166L, 1996.
ATP stimulation of surfactant secretion in type II cells is mediated by both a P2Y2 receptor coupled to phospholipase C and a receptor coupled to adenylate cyclase. UTP also activates the P2Y2 receptor but does not stimulate adenosine 3',5'-cyclic monophosphate (cAMP) formation. We have examined surfactant secretion and signaling parameters in response to ATP and UTP in type II cells from newborn rats. There was a developmental increase in the response to both agonists. However, whereas ATP increased secretion as early as day 1, the effect of UTP did not become significant until 4 days after birth. ATP increased cAMP formation as early as day 1 but did not promote diacylglycerol formation or phospholipase D activation until day 4. Thus the adenylate cyclase-coupled ATP signaling mechanism is functional early in development but the P2Y2 pathway is not. We therefore used type II cells from 1-2 day old rats to investigate the adenylate cyclase-coupled mechanism in the absence of interactions with the P2Y2 system. Effects of ATP and 5'(N -ethylcarboxyamido)adenosine (NECA) on surfactant secretion and cAMP formation were not additive and their effects on secretion were antagonized by the same adenosine receptor antagonists. Overnight culture of the cells with NECA almost completely abolished the subsequent increase in cAMP formation in response to NECA, adenosine and ATP but not to terbutaline. These data suggest that ATP, NECA and adenosine activate the same receptor. Effects of ATP were not decreased by adenosine deaminase showing that they are not mediated by adenosine acting directly at adenosine receptors. We suggest that ATP directly activates an adenosine receptor on the type II cell. 

Received 3 July 1996; accepted in final form 16 September 1996.
APS Manuscript Number L204-6.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996