Adaptive response of cultured fibroblasts to hyperosmolarity

Raising to 0.4 osM the osmolarity of the medium in which chick embryo fibroblasts are incubated quickly increases the internal Na+ concentration, inhibits protein synthesis and also stimulates amino acid transport. On extending the incubation time, cells appear to adapt to the altered environment, as the Na+ content declines toward control values within few hours. Protein synthesis resumes its normal rate within 12-14 h of treatment. Experimental alteration of the monovalent cation content by substituting extracellular Na+ with other osmolites or by using ouabain or the ionophore monensin reveals an impairment of protein synthesis. Analysis by SDS-PAGE reveals an alteration of the polypeptide pattern expressed by hyperosmolarity-exposed cells, resulting in an enhanced synthesis of the 87, 75 and 53 kD proteins and inhibition of a 125 kD band. The previously increased amino acid transport activity also reverts to its normal level, but only after 40-50 h of incubation. The growth rate of these cells does not appear to be significantly affected during the first 3 days of the hyperosmolar treatment. Results presented in this publication identify the alteration of the protein synthesis rate, the change in the intracellular cation content and the increase in amino acid transport activity as plausible parameters of adaptive response, and suggest that the modulation of gene expression observed in cells exposed continuously to hyperosmolarity may be a consequence of the alteration of the intracellular monovalent cation concentration.