Affiliation:
1. Department of Physiology, University of Innsbruck, A-6020 Innsbruck, Austria
Abstract
Pulmonary surfactant is secreted via exocytosis of lamellar bodies (LBs) by alveolar type II cells. Here we analyzed the dependence of LB exocytosis on intracellular Ca2+concentration ([Ca2+]i). In fura 2-loaded cells, [Ca2+]iwas selectively elevated by flash photolysis of a cell-permeant caged Ca2+ compound ( o-nitrophenyl EGTA-AM) or by gradually enhancing cellular Ca2+influx. Simultaneously, surfactant secretion by single cells was analyzed with the fluorescent dye FM 1-43, enabling detection of exocytotic events with a high temporal resolution (T. Haller, J. Ortmayr, F. Friedrich, H. Volkl, and P. Dietl. Proc. Natl. Acad. Sci. USA 95: 1579–1584, 1998). Exocytosis was initiated at a threshold concentration near 320 nmol/l with both instantaneous or gradual [Ca2+]ielevations. The exocytotic response to flash photolysis was highest during the first minute after the rise in [Ca2+]iand thus almost identical to purinoceptor stimulation by ATP. Correspondingly, the effects of ATP on initial secretion could be sufficiently explained by its ability to mobilize Ca2+. This was further demonstrated by the fact that exocytosis is significantly blocked by suppression of the ATP-induced Ca2+ signal below ∼300 nmol/l. Our results suggest a highly Ca2+-sensitive step in LB exocytosis.
Publisher
American Physiological Society
Subject
Cell Biology,Physiology (medical),Pulmonary and Respiratory Medicine,Physiology
Cited by
55 articles.
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