Biochemical studies of the excitable membrane of Paramecium tetraurelia. VIII. Temperature-induced changes in lipid composition and in thermal avoidance behavior

Transfer of a culture of Paramecium tetraurelia from 25 to 35°C produced several significant changes in membrane lipid composition within 4 h. The proportion of gg-linolenic acid (γ18:3) decreased, the ratio of 16:0 to 18:0 in sphingolipids decreased, and the ratio of 7-dehydrocholesterol to 7-dehydrostigmasterol increased at the higher temperature. When cultures were transferred from 35 back to 25°C, these changes were reversed within 4 h. The lipid alterations induced by a temperature shift occurred both in ciliary membranes and in deciliated bodies, but were most striking in ciliary membranes. The shift up in culture temperature caused a slight reduction in the proportion of ciliary unsaturated fatty acids within 8 h. However, after two days at 35°C the proportion of unsaturated fatty acids of ciliary membranes was not different from that of ciliary membranes from cells cultured at 25°C. Coincident with the changes in membrane lipid composition, thermal avoidance behavior of paramecia also changed after a shift from 25 to 35°C. Cells incubated at the higher temperature showed less thermal avoidance, but reacquired it after being transferred back to 25°C. The changes in thermal avoidance behavior occur in parallel with changes in membrane lipid composition, suggesting that the membrane lipid may be involved in thermosensory transduction.