SURFACE-MEDIATED DEATH OF UNCONDITIONED TETRAHYMENA CELLS - EFFECT OFPHYSICAL PARAMETERS, GROWTH-FACTORS, HORMONES, AND SURFACTANTS

A new form of cell death has been observed. The death occurs at liquid -air interfaces when Tetrahymena cells are grown in a chemically defin ed medium (CDM) at low inocula. The cells die by lysis at the liquid-a ir interface (medium surface), which they reach due to negative gravit axis as well as positive aerotaxis. When the cells are grown in a clos ed compartment, with no liquid-air interface, the death is not observe d, and the cells proliferate. Cloning of cells in CDM is thus possible . The addition of effectors such as NGF (10(-11) M), EGF (10(-10) M), PDGF (10(-10) M), and insulin (10(-7) M) to cells in CDM prevents the surface mediated death. Since detergents/surfactants like SDS (7 x 10( -5) M), NP-40 (2 x 10(-5) M), Tween 80 (10(-4)% w/v), Pluronic F-68 (1 0(-7) M), and the biosurfactant surfactin (10(-6) M) have the same eff ect, we suggest that the effecters act by stimulating the cells to exu date surfactant(s) of their own. Furthermore, lyzed cells and exudates from living cells (pre-conditioned medium) prevent the death. In cond itions with liquid-air interfaces, certain physical parameters are of great importance for the survival of cells at low inocula. The paramet ers are the distance to the surface, the temperature, and the inoculum . By increasing the height of the medium, lowering the temperature, an d increasing the inoculum of the culture, the survival can be greatly enhanced. There is no evidence for programmed cell death (PCD) or apop tosis. (C) 1996 Wiley-Liss, Inc.