AN ISOTHERMAL INDUCTION OF DELTA(9)-DESATURASE IN CULTURED CARP HEPATOCYTES

Cold exposure of carp leads to the induced activity of the hepatic Del ta(9)-desaturase (Schunke, M. and Wodtke, E. (1983) Biochim. Biophys, Acta 734, 70-75). We have investigated the controlled expression of th is enzyme using isolated carp hepatocytes. Culture at 30 degrees C, of cells isolated from 30 degrees C-acclimated carp, resulted in an 8-13 -fold increase in desaturase-specific activity over 4 days, whilst ano ther enzyme of intermediary metabolism, glucose-6-phosphatase, decreas ed by more than 60%. This desaturase induction was associated with a l oss of intracellular lipid vesicles and with increases in the levels o f oleic acid of membrane phosphoglycerides and corresponding decreases in 22:6(n - 3). Supplementation of cultures with oleic acid and with polyunsaturated fatty acids did not cause any reduction in the desatur ase induction. The level of immunodetectable desaturase protein increa sed during culture at 30 degrees C and a desaturase mRNA was detected after 2 days of culture by Northern analysis. These results suggest th at in vitro culture leads to an increased synthesis of desaturase prot ein by means of activated gene transcription. Significantly, transfer of cultures of 30 degrees C-acclimated hepatocytes to 10 degrees C res ulted in a smaller induction of desaturase activity; thus cold transfe r of cells in itself did not induce hepatocyte desaturase activity as does whole animal cooling. This suggests either that cold induction of desaturase activity in vivo involves systemic control or that the con ditions imposed by culture prevent cold induction.