Reversible compression of cytoplasm

Abstract

Incubation for 3 min in 1 M sorbitol causes animal cells to lose 50–75% of their water content. Upon return to normal medium, the ultrastructure and morphology of the cells return to normal within 3 min. Mitoses continue normally; migration patterns and growth curves also return to normal. An intriguing aspect of irreversibility was observed when blebbing microplasts switched to ruffling. They would have continued to bleb without the prior episode of dehydration in sorbitol. During incubation with 1 M sorbitol the shrunken cells appear to store excess surface area in numerous, rapidly forming microvilli. The cytoplasm is also altered. Bundles of individual microfilaments and intermediate filaments condense into homogeneous streaks of materials which retain their birefringence. In contrast, microtubules display a clearly visible exclusion zone around each individual tubule. Sharply outlined patches of tiny granules appear in electron micrographs. The results are discussed with respect to the morphological compartmentalization and the viscoelasticity of the cytoplasm.