ADAPTIVE CELLULAR-RESPONSE TO OSMOTIC-STRESS IN PIG ARTICULAR CHONDROCYTES

The authors studied the effects of a wide range of medium osmolarities (from 0.28 osM (physiological osmolarity of plasma and synovial fluid ) to 0.58 osM) by altering Na+ concentration in high density cultures of pig articular chondrocytes in order to analyze the behaviour of som e functional and structural parameters during cell adaptation to these imposed changes in the ionic environment. Biochemical and morphologic al results indicated that, even if isolated from the tissue matrix and cultured in vitro, chondrocytes maintained active osmoregulation syst ems which are present in living conditions. They showed a similar bioc hemical and morphological behavior when cultured at 0.28 osM and 0.38 osM but they were able, with regard to protein synthesis, aminoacid tr ansport and proliferation rates, to respond quickly and to adapt to 0. 48 osM medium as well. On the contrary, the treatment at the highest o smolarity (0.58 osM) early altered these biochemical parameters and wa s detrimental or even gave rise to lethal damage during long-term trea tment. Furthermore, while chondrocytes cultured in 0.28-0.38 osM mediu m maintained phenotypic characteristics in culture, the higher osmolar ities (0.48-0.58 osM) caused morphological changes in cell populations resulting in loss of phenotypic cell stability as demonstrated by the ir taking on a fibroblast-like shape as well as a lack of ability to a ssembly matrix proteoglycans.