Calcium signaling in human airway goblet cells following purinergic activation

Despite the general importance of Ca2+ signaling in signal transduction, and of goblet cell mucin hypersecretion in inflammatory pulmonary diseases, measurement of airway goblet cell intracellular Ca2+ (Ca-i(2+)) has not been reported. In this article, we describe the results of experiments measuring Ca-i(2+) in primary cultures of human bronchial goblet cells after stimulation with the purinergic agonist adenosine 5'-O-(3-thio-triphosphate) (ATP gamma S) and phorbol 12-myristate 13-acetate (PMA). Ca2+ signaling in human goblet cells after purinergic stimulation follows the classic paradigm of a Ca-i(2+) transient from a basal activity of 110 nM to a peak response of 260.1 +/- 41.2 nM within 2 min, followed by a long superbasal plateau (155.3 +/- 0.2 nM) between 10 and 15 min. The rise in Ca-i(2+) appears to result from a mobilization of intracellular stores, because the transient was nearly abolished by inhibition of PLC with the phosphatidylinositol-specific PLC inhibitor U-73122, and it was not affected significantly by removal of extracellular Ca2+. Loading goblet cells with BAPTA inhibited the ATP gamma S-induced Ca2+ transient by 86.0 +/- 13.1%, relative to control. Finally, in contrast to the massive effects of high doses of PMA (300 nM) on mucin secretion from goblet cells, phorbol ester stimulated a small (27.1 +/- 7% of the ATP gamma S control peak), brief rise in Ca-i(2+). This diminutive signal likely denotes a local Ca2+ gradient, which may be associated with the mucin granule exocytotic process.