HEPATOMA McARDLE-RH7777 CELLS HAVE THE SAME RESPONSE AS NORMAL RAT HEPATOCYTES TO BOTH DIBUTYRYL-cAMP AND ANTICALMODULINW-7

The effects of cAMP-analogue dibutyryl-cAMP and anticalmodulin W-7 were studied on de novo synthesis and secretion of lipids in cultures of hepatoma McArdle RH7777 cells and normal rat hepatocytes. Dibutyryl-cAMP and W -7 separately caused a significant decrease in the secretion of de novo synthesized triacyl [3H]glycerol in both cultures of McArdle cells and rat hepatocytes. The inhibitory effects of dibutyryl-cAMP and W-7 were concentration-dependent and appeared at the lowest concentration examined, 5JlM and 20JlM respectively. DibutyrylcAMP at a concentration of 50 JlM and W -7 (20 µM) suppressed the secretion of triacylglycerol by approx. 38% (p<0.05) and 37% (p<0.05) respectively. Dibutyryl.cAMP but not W -7 also suppressed the secretion of phosphatidylcholine significantly. Dibutyryl-cAMP and W-7 had no significant effect upon [3H]glycerollabeled de novo formed triacylglycerol and phosphatidylcholine, except at the highest concentration tested, 500JlM and 50JlM respectively, where both triacylglycerol and phosphatidylcholine synthesis were suppressed significantly. Similar findings were obtained on cultured hepatocytes. The molar ratios of newly made triacylglycerol/phosphatidyl choline in the media and cells of hepatocytes were about four times compared to that of McArdle cells, indicating more lipidation and core expansion of nascent lipoprotein particles in hepatocytes. The molar ratio of triacylglycerol/phosphatidyl choline in the medium and cells of cultured McArdle cells was unchanged significantly i n the presence of either dibutyryl-cAMP or W-7. However, the molar ratio was decreased 25% (p<O.Ol) in the presence of dibutyryl-cAMP in the media but not in the cells of cultured hepatocytes. These results suggest that hepatoma McArdle cell's response to both cAMP-analogue and calmodulin antagonist are comparable to that of normal rat hepatocytes. In addition, the inhibitory effects of dibutyryl-cAMP and W-7 at low concentration are unlikely to be due to the suppression oftriacylglycerol and phosphatidyl choline synthesis.