Lamellar body secretion in cyclically stretched rat alveolar type II cells depends on the geometry of cell‐cell interaction

Abstract

Alveolar type II cells respond to mechanical stimulation with a fusion of surfactant containing lamellar bodies (LBs) with the cell membrane. Single fusion events of LBs can be detected with the fluorescent dye FM1‐43 in vitro which was used to investigate the effect of cyclic stretch on LB exocytosis in primary rat type II cells. After cultivating the cells on an elastic growth support we used a micro‐robotic arm (kleindiek nanotechnik) that allowed us to locally stretch the underlying growth substrate and hence to apply unidirectional stretch to individual clusters of cells. Stretch of different frequencies (1, 2 and 4hz) revealed that the fusion response was inversely related to the frequency but only slighly lower (1.84Hz) in responders as compared to non‐responders (2.0Hz). Also the stretch amplitude (from 1 to 25%) did barely correlate with the number of LB fusions. Cells that responded with fusions were generally attached to more cells than the ones without response indicating cell‐cell interaction of some kind to account for the process. In cases were the position of the adjacent cells with respect to the stretch axis could precisely be defined, we found that an unsymmetric deformation rather than simple elongation of a cell cluster lead to an increased number of fusions. Latter shows that the mechanosensitive machinery of the ATII cell is able to distinguish between force patterns and we suggest cytoskeletal elements to be a key player in mediating this process.Supported by the FWF, grant P15743, the DFG, grant D1402, the Landesstiftung Baden‐Württemberg and the 6th framework of the EU, Pulmo‐Net.