CALCIUM-DEPENDENT CHLORIDE SECRETION ACROSS CULTURES OF HUMAN TRACHEAL SURFACE EPITHELIUM AND GLANDS

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 ([Ca2+]i). Short-circuit curr ent (I(SC)), an index of transepithelial active ion transport, was mea sured on cells from the same cultures. Surface epithelial [Ca2+]i of 8 2 +/- 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 [Ca2+]i in cultured gland cells of 68 +/- 11 nM was increased transiently by isoproterenol, hist amine, methacholine, and bradykinin with maximal increases of 105 +/- 19, 233 +/- 47, 327 +/- 121, and 634 +/- 151 nM (n = 17-21), respectiv ely. In both cell types, mediators that increased [Ca2+]i also increas ed I(SC) with a time course identical to the increase in [Ca2+]i. Pret reatment 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 b oth the I(SC) and [Ca2+] i responses to agonists. Forskolin (10(-5) M) , 3-isobutyl-1-methylxanthine (10(-3) M), dibutyryl adenosine 3',5'-cy clic monophosphate (10(-3) M), and 8-(4-chlorophenylthio)-cAMP (10(-3) M) had no or only trivial effects on I(SC) and [Ca2+]i. We suggest th at mediators increase I(SC) across human airway epithelium by activati ng Ca-dependent basolateral K channels, resulting in hyperpolarization and an increased driving force for Cl exit through apical membrane Cl channels.