FATTY-ACID MODIFICATION OF MEMBRANE FLUIDITY IN CHINESE-HAMSTER OVARY(TR715-19) CELLS

Dietary saturated fatty acids, especially lauric (12:0), myristic (14: 0) and palmitic (16:0) acids, which are hypercholesterolemic, influenc e cell membrane fatty acid composition and affect LDL receptor functio n, When membrane phospholipid fatty acids in Chinese hamster ovary cel ls, containing the human LDL receptor, were modified (Hannah J. S. et al., 1995 Metabolism 44, 1428-1434), LDL receptor function was affecte d, but correlations with DPH-determined membrane fluidity were weak, T he role of fluidity in various membrane domains with respect to the LD L receptor is examined here, Membrane fluidity was assessed by measuri ng steady-state fluorescence polarization of diphenylhexatriene (DPH) and its polar propionic acid (DPH-PA) and trimethylammonium (TMA-DPH) derivatives from 38 to 4 degrees C in fatty acid modified Chinese hams ter ovary cells, Fatty acid changes modulated mid-bilayer fluidity as determined with DPH, but fluidity in phospholipid headgroup domains, a ssessed with DPH-PA and TMA-DPH, was independent of fatty acyl composi tion, The I)PH fluidity was related to membrane unsaturation (P < 0.02 ), oleate contents (P < 0.009) in particular, but inversely related (P < 0.0002) to the longer chain (greater than or equal to 20 C atoms) u nsaturated fatty acids with from four to six double bonds, The LDL bin ding was independent of fluidity, but there were weak relations betwee n LDL internalization and DPH-PA anisotropy and between LDL degradatio n and TMA-DPH anisotropy, It was concluded that LDL binding was not re lated to mid-bilayer fluidity, but the results with the polar probes s uggest a role of fluidity in modulating vertical displacement of the L DL/LDL receptor complex across the plasma membrane.