Calcium-dependent chloride secretion across cultures of human tracheal surface epithelium and glands
Yamaya, M.; Ohrui, T.; Finkbeiner, W.E.; Widdicombe, J.H.
American Journal of Physiology 265(2 Pt 1): L170-L177
1993
ISSN/ISBN: 0002-9513 PMID: 8396338 Document Number: 411951
Surface epithelium and gland cells from human trachea were cultured on porous-bottom inserts and loaded with fura 2 to permit measurement of the intracellular calcium concentration ((Ca-2+)-i). Short-circuit current (I-sc), an index of transepithelial active ion transport, was measured on cells from the same cultures. Surface epithelial (Ca-2+)-i of 82 +- 15 nM was increased transiently by isoproterenol, histamine, and bradykinin with maximal increases of 88 +- 17, 480 +- 149, and 978 +- 214 nM (n = 15), respectively. Baseline (Ca-2+)-i in cultured gland cells of 68 +- 11 nM was increased transiently by isoproterenol, histamine, methacholine, and bradykinin with maximal increases of 105 +- 19, 233 +- 47, 327 +- 121, and 634 +- 151 nM (n = 17-21), respectively. In both cell types, mediators that increased (Ca-2+)-i also increased I-sc with a time course identical to the increase in (Ca-2+)-i. Pretreatment with the calcium chelator, 1,2-bis-(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid, acetoxymethyl ester (BAPTA-AM), had no effect on basal I-sc or transepithelial resistance but markedly inhibited both the I-sc and (Ca-2+)-i responses to agonists. Forskolin (10-5 M), 3-isobutyl-1-methylxanthine (10-3 M), dibutyryl adenosine 3',5'-cyclic monophosphate (10-3 M), and 8-(4-chlorophenylthio)-cAMP (10-3 M) had no or only trivial effects on I-sc and Ca-2+)-i. We suggest that mediators increase I-sc across human airway epithelium by activating Ca-dependent basolateral K channels, resulting in hyperpolarization and an increased driving force for Cl exit through apical membrane Cl channels.