High temperature-induced changes in the organization of the microfilament system and cell membrane activity in Amoeba...

The response of Amoeba proteus to heating from 22°C to 45°C starts with the inhibition of locomotion when the temperature of the culture medium reaches about 32°C. All following morphological reactions which lead to the formation of spherical forms result from a centripetal contraction of the whole cell body along the former axis of migration. This contraction and changes in shape are closely correlated to alterations in the organization of the microfilament system and the cell membrane behaviour. During the initial phase of contraction, the cells first attain an irregular shape with a heavily folded surface and form thick plaques of microfilaments at distinct places beneath the cell membrane. Later, the filamentous plaques disappear probably as a consequence of further contraction and eventual destruction of the system. Destabilization and an increased fluidity of the cell membrane as induced by higher temperatures as well as controlled shifts in the equilibrium between actin assembly and disassembly and the increased synthesis of actin binding proteins are discussed as possible reasons for the described transformations.