Multiple intracellular pathways for regulation of chloride secretion in cultured pig tracheal submucosal gland cells

Tracheal submucosal glands are of great relative importance in the secretion of chloride and water to the airway lumen. This study aimed to examine whether the cystic fibrosis transmembrane conductance regulator (CFTR) is involved in cyclic adenosine monophosphate (cAMP) or Ca2+-activated Cl- secretion. Regulation of Cl- secretion in cell cultures derived from pig tracheal submucosal gland acini was investigated by X-ray microanalysis. With or without preincubation with CFTR antisense oligodeoxynucleotide (5 microM). A significant decrease in cellular Cl and K concentration was induced by 5 mM 8-bromo-adenosine 3': 5'-cyclic monophosphate (8-bromo-cAMP), 3 microM calcium ionophore ionomycin, 200 microM 5'-uridine triphosphate (UTP) and 200 microM 5'-adenosine triphosphate (ATP), respectively. The decrease in cellular Cl content was significantly inhibited by the Cl- channel blocker 5-nitro-2-(3-phenylpropyl-amino)-benzoic acid (NPPB; 50 microm). Preincubation of the cells with CFTR antisense oligodeoxynucleotide significantly inhibited the 8-bromo-cAMP-induced decrease in Cl, whereas CFTR sense oligodeoxynucleotide had no effect. The effects of ionomycin, ATP or UTP were not blocked by either CFTR antisense oligodeoxynucleotide or CFTR sense oligodeoxynueleotide. To measure the cytosolic free calcium concentration ([Ca2+]i) the cells grown on glass coverslips were loaded with fura-2 tetraoxymethylester (fura-2 AM; 5 microM). The [Ca2+]i was measured as the fluorescence ratio of emission (340/380 nm). Ionomycin (3 microM) caused a rapid increase in [Ca2+]i followed by a sustained plateau, but 8-bromo-cAMP had a more complex effect on [Ca2+]i. Exposure to ATP or UTP caused a rapid increase in [Ca2+]i followed by a decrease. In conclusion, cystic adenosine monophosphate and ionomycin induced Cl- secretion through different intracellular pathways. Adenosine triphosphate and uridine triphosphate also induced Cl- secretion probably with Ca as an intracellular messenger. The cystic fibrosis transmembrane conductance regulator is not involved in Cl- secretion activated by extracellular adenosine triphosphate and uridine triphosphate.

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