Purinergic Regulation of Ion Transport Across Nonciliated Bronchiolar Epithelial (Clara) Cells

Previous studies demonstrated that elevation of intracellular calcium concentration ([Ca2+]i) increased electrogenic anion transport by bronchiolar epithelia. Extracellular nucleotides were shown to elevate [Ca2+]i and transepithelial short-circuit current (Isc) in proximal airways epithelia. In this study purine and pyrimidine nucleotides were investigated for their ability to regulate ion transport by rabbit nonciliated bronchiolar epithelial (Clara) cells in culture. ATP in the apical bath induced a concentration-dependent transient increase in [Ca2+]i and Isc. Mean effective doses (ED50) of the responses were 10(-7) M and 10(-6) M, respectively. Transepithelial resistance (Rt) decreased. The peak changes in Isc and Rt were 7.8 +/- 1.2 microA/cm2 and -59 +/- 14 omega.cm2 (n = 26, basal Isc = 47.4 +/- 4.3 microA/cm2 and Rt = 428 +/- 40 omega.cm2). Some preparations exhibited a small residual increase in Isc after the initial response, but the change was not statistically significant (delta Isc = 1.7 +/- 1.2 microA/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-methylthio-ATP, and alpha, beta-methylene-ATP had negligible effects on the peak delta Isc and subsequent stimulation by ATP. The ionic mechanism underlying the ATP-induced increase in Isc was investigated with the use of specific ion-transport inhibitors and by ion substitution.(ABSTRACT TRUNCATED AT 250 WORDS)