Purinergic regulation of ion transport across nonciliated b ronchiolar epithelial (clara) cells. Van, Michael R., Scott, Thierry C. Chinet, Angela D. Burnette, and Anthony M. Paradiso. East Carolina University, Greenville, North Carolina 27858; and University of North Carolina, Chapel Hill, North Carolina 27599
APStracts 2:0040L, 1995.
Previous studies demonstrated that elevation of intracellular calcium con centration (Cai) increased electrogenic anion transport by bronchiolar epithelia. Ex tracellular nucleotides were shown to elevate Cai and transepithelial short circuit current (Isc) in proximal airways epithelia, and in this study purine and pyrimidine nucleotides were therefore investigated for their ability to regulate the ion transport by rabbit nonciliated bronchiolar epithelial (Clara) cells in culture. ATP in the apical bath induced a concentration-dependent transient increase in Cai and Isc. ED50,s of the responses were 10-7M and 10-6M, respectively. Transepithelial resistance (Rt) decreased. The peak changes in Isc and Rt were 7.8+/ -1.2 [mu]A/cm2 and -59+/-14 W x cm2 (n=26, basal Isc = 47.4+/-4.3 [mu]A/cm2 and Rt = 428+/-40 W x cm2). Some preparations ex hibited a small residual increase in Isc following the initial response, but the change was not statistically significant (DIsc = 1.7 +/- 1.2 [mu]A/cm2, n=18). Addition of ATP to the basolateral bath had no detectable effects. Purinoceptor agonists were used to characterize the receptors mediating the change in Isc. UTP and ATP[gamma]S increased Isc and inhibited subsequent stimulation by ATP. ADP, ADP[beta]S, 2-methylthioATP, and a,b-methyleneATP had negligible effects on the peak DIsc and subsequent stimula tion by ATP. The ionic mechanism underlying the ATP-induced increase in Isc was investigated using specific ion transport inhibitors and by ion substitution. The peak DIsc was not inhibited by amiloride in the apical bath, bumetanide in the basolateral bath, bilateral Cl- free KBR, or bilateral HCO3-/CO2-free Ringer. Substitution of NMDG for Na+ in the basolateral bathing solution and bilateral substitution of g luconate for both Cl- and HCO3- inhibited the peak DIsc. When preparations were pretreated with a combination of bilateral HCO3 -/CO2-free Ringer and amiloride in the apical bath to unmask Cl- secretion, ATP induced a large increase in Isc that was inhibited by bumetanide in the basolateral bath. These results indicated that activa tion of P2U purinoceptors in the apical membrane of Clara cells mobilized intracellular Cai and stimulated electrogenic secretion of Cl- and HCO3-. 

Received 6 September 1994; accepted in final form 1 March 1995.
APS Manuscript Number L261-4.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  4 April 1995.