Cyclic stretch induces both apoptosis and secretion in rat alveolar type II cells

We examined the effects of short-term cyclic stretch on both phosphatidylcholine (PC) secretion and apoptosis in primary cultures of rat alveolar type II cells. A 22% cyclic stretch (3 cycles/min) was applied to type II cells cultured on silastic membranes using a Flexercell strain unit. This induced, after a lag period of about 1 h, a small, but significant release of [3H]PC from prelabelled cells. In addition, stretch increased nuclear condensation, the generation of oligosomal DNA fragments and the activation of caspases. Similar responses were triggered by sorbitol-induced osmotic shock, but not by the secretagogue ATP. We conclude that stretch can induce both apoptosis and PC secretion in alveolar type II cells and propose that these diverse responses occur within the lung as a consequence of normal respiratory distortion of the alveolar epithelium.