Simulated microgravity impairs respiratory burst activity in human promyelocytic cells

The concept of microgravity (free-fall) influencing cellular functions in n onadherent cells has not been a part of mainstream scientific thought. Util izing rotating wall vessels (RWVs) to generate simulated microgravity condi tions, we found that respiratory burst activity was significantly altered i n nonadherent promyelocytic (HL-60) cells. Specifically, HL-60 cells in sim ulated microgravity for 6, 19, 42, 47, and 49 d had 3.8-fold fewer cells th at were able to participate in respiratory burst activity than cells from 1 x g cultures (P = 0.0011, N = 5). The quantity of respiratory burst produc ts from the cells in simulated microgravity was also significantly reduced. The fold increase over controls in mean fluorescence intensities for oxida tive products from cells in microgravity was 1.1 +/- 0.1 versus 1.8 +/- 0.3 for cells at 1 X g (P = 0.013, N = 4). Furthermore, the kinetic response f or phorbol ester-stimulated burst activity was affected by simulated microg ravity. These results demonstrate that simulated microgravity alters an inn ate cellular function (burst activity). If respiratory burst activity is im paired by true microgravity, then recovery from infections during spaceflig ht could be delayed. Finally, RWVs provide an excellent model for investiga ting the mechanisms associated with microgravity-induced changes in nonadhe rent cells.