The effect of osmolarity on metabolism and morphology in adhesion and suspension chinese hamster ovary cells producing tissue plasminogen activator

The effects of constant osmolarity, between 300 and 500 mOsm/kg, on the metabolism of Chinese Hamster Ovary (CHO) cells producing tissue plasminogen activator (tPA) were compared between adhesion and suspension cultures. In both suspension and adhesion culture, the specific rates of glucose consumption (nu(G)), lactate production (q(L)), and tPA production (q(tPA)) increased as osmolarity increased, while these rates decreased when osmolarity was higher than the respective critical levels. However, specific growth rate (mu) decreased with increase in osmolarity and this slope grew steeper in the osmolarity range higher than the critical level. The decrease in mu in the adhesion culture was more rapid than that in the suspension culture. The critical osmolarity for adhesion culture (400 mOsm/kg) was lower than that for suspension culture (450 mOsm/kg). These results indicated that the adhesion culture was more sensitive to increase of osmolarity than the suspension culture, while the specific rates obtained from the adhesion cultures were in general 1.5- to 3-fold higher than those obtained from the suspension cultures. Cell volume increased as osmolarity increased in both the suspension and adhesion cultures, as reported previously for suspension culture of hybridoma cells, but there was no morphological change in the suspension culture. In contrast, cell height decreased and cell adhesion area markedly increased as osmolarity increased in the adhesion culture. This morphological change in adhesion cultures may be one reason for the higher sensitivity of adherent cells to the increase of osmolarity than suspended cells.