CULTURED HUMAN SKIN FIBROBLASTS MODIFY THEIR PLASMA-MEMBRANE LIPID-COMPOSITION AND FLUIDITY ACCORDING TO GROWTH TEMPERATURE SUGGESTING HOMEOVISCOUS ADAPTATION AT HYPOTHERMIC (30-DEGREES-C) BUT NOT AT HYPERTHERMIC (40-DEGREES-C) TEMPERATURES

Mammalian cell metabolism is responding to changes in temperature. Body temperature is regulated around 37-degrees-C, but temperatures of exposed skin areas may vary between 20-degrees-C and 40-degrees-C for extended periods of time without apparent disturbance of adequate cellular functions. Cellular membrane functions are depending from temperatures but also from their lipid environment, which is a major component of membrane fluidity. Temperature-induced changes of membrane fluidity may be counterbalanced by adaptive modification of membrane lipids. Temperature-dependent changes of whole cell- and of purified membrane lipids and possible homeoviscous adaptation of membrane fluidity have been studied in human skin fibroblasts cultured at 30-degrees-C, 37-degrees-C and 40-degrees-C for ten days. Membrane anisotropy was measured by polarized fluorescence spectroscopy using TMA-DPH for superficial and DPH for deeper membrane layers. Human fibroblasts were able to adapt themselves to hypothermic temperatures (30-degrees-C) by modifying the fluidity of the deeper apolar regions of the plasma membranes as reported by changes of fluorescence anisotropy due to appropriate changes of their plasma membrane lipid composition. This could not be shown for the whole cells. At 40-degrees-C growth temperature, adaptive changes of the membrane lipid composition, except for some changes in fatty acid compositions, were not seen. Independent from the changes of the membrane lipid composition, the fluorescence anisotropy of the more superficial membrane layers (TMA-DPH) increased in cells growing at 30-degrees-C and decreased in cells growing at 40-degrees-C.