From angels to handmaidens: changing constructions of nursing's public image in post-war Britain

The molecular and ionic mechanisms responsible for the regulation of mucus exocytosis in human airway gland cells remain poorly defined. To determine whether dynamic changes of intracellular free Ca2+ concentration Ca2+]i can promote different exocytotic responses, we monitored dynamic changes in Ca2+]i and secretory granule (SG) exocytosis in individual human tracheal submucosal serous gland (HTG) cells. These changes were in response to exposure of the cells to three different secretagogues associated with airway inflammation and disease: human neutrophil elastase (HNE), histamine, and ATP. Dynamic changes in Ca2+]i from single cells were determined with Indo-1/AM using quantitative UV laser microspectrofluorometry. The rate of SG exocytosis was measured in single cells by fluorescence videomicroscopy of SG degranulation and by the ELISA method. Exposure of HTG cells to a low concentration of HNE (1.0 microM) caused a high rate of SG exocytosis (52% decrease in the initial quinacrine fluorescence) during the first 8-min stimulation period compared with that observed following exposure of the cells to 100 microM histamine (10% decrease) or 100 microM ATP (6% decrease). In contrast to a rapid and transient rise in Ca2+]i induced by histamine (1.0-100 microM) and ATP (10-100 microM), HNE (0.01-1 microM) generated asynchronous oscillations in Ca2+]i over the first 8-min period. Depletion of internal Ca2+ stores with thapsigargin (500 nM) induced a significant reduction (P < 0.01) in the observed increases in Ca2+]i upon addition of each of the secretagogues, but did not greatly affect the SG exocytotic responses. Interestingly, the removal of extracellular Ca2+ (+5 mM EGTA) significantly reduced (P < 0.01) both the Ca2+]i increases and the rate of SG exocytosis following exposure to the secretagogues. We also demonstrate that the influx of extracellular Ca2+ and Ca2+]i oscillations rather than the absolute level of Ca2+]i regulate the rapid onset and extent of exocytotic responses to HNE in airway gland cells. Taken together, these results provide strong evidence that Ca2+]i is a critical intracellular messenger in the regulation of exocytosis process in human airway gland cells.