An extended release for surfactant

Most think of exocytosis as an instantaneous process that once started cannot be fine-tuned. But on page 279, Haller et al. describe the exocytosis of surfactant from specialized lung cells (alveolar type II cells), and find that the degree and rate of pore expansion can be modified, thus controlling the rate of release of this vital agent from open pores.The authors gauge the extent of pore opening by adding a dye, and comparing the rate of its accumulation in either free surfactant or surfactant that remains trapped in open pores. The relative rates give a measure of the opening of the pores, and indicate that opening can be slow initially before a later expansion or, occasionally, retraction. Pores can remain open for as long as several hours. Continuous measurements of pore behavior were made by using an intermediate laser strength...