Effect of serum on the plasma membrane fluidity of hybridomas: an insight into its shear protective mechanism.

We have previously shown that decreasing the concentration of fetal bovine serum (FBS) increased the fragility of a mouse hybridoma (HB-32) during agitated batch cultivation and that increasing the plasma membrane fluidity (PMF) increased the shear sensitivity during exposure to laminar flow. In this study, the effect of FBS concentration on the PMF of HB-32 was investigated. PMF was evaluated by steady-state fluorescence anisotropy (rs) of 1-[4-(trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene. Increasing serum concentration increased the rs of hybridomas, indicating a decrease in their PMF. The effect of cholesterol modulation on the PMF and shear sensitivity was also evaluated. Hybridomas were exposed to turbulent fluid shear after modification of PMF by cholesterol modulation. Direct cholesterol enrichment of the plasma membranes caused a decrease in the PMF and shear sensitivity, while cholesterol depletion caused an increase in PMF and shear sensitivity. Low- and high-density lipoprotein supplementation to cultures in serum-free or complete medium decreased their shear sensitivity. Lipoprotein supplementation to serum-free cultures decreased the PMF. Altogether, these results suggest that the protective mechanism of serum against hydrodynamic damage relies, at least partially, on its ability to decrease the PMF of hybridomas possibly through the transfer of cholesterol from the serum lipoproteins into the plasma membrane.