Receptors for insulin and other hormones are often influenced by their environment, including fatty acid content and membrane fluidity. Y79 retinoblastoma cells enriched with arachidonic or docosahexaenoic acid show an increase in membrane fluidity determined by fluorescence polarization using the plasma membrane-specific probe, trimethylammonium-diphenylhexatriene. Unlike cells enriched with polyunsaturated fatty acids, cells cultured in media containing palmitic or oleic acid showed no changes in membrane fluidity or fatty acid composition. Cells enriched with docosahexaenoic acid show an increase in insulin binding at 15 degrees C that is due to an increase in the number of available insulin receptor sites on the plasma membrane. In contrast, insulin binding is not altered in cells enriched with arachidonic, palmitic or oleic acid. Furthermore, the binding of insulin-like growth factor-I (IGF-I) in Y79 cells is not changed by the fatty acid unsaturation of the cell membrane. Because docosahexaenoic acid is naturally present in high concentrations in the retina these studies suggest it may have a role in modulating insulin binding and function.