Decreased myo‐lnositol Uptake Is Associated with Reduced Bradykinin‐Stimulated Phosphatidylinositol Synthesis and Diacylglycerol Content in Cultured Neuroblastoma Cells Exposed to L‐Fucose

Abstract

L-Fucose is a potent, competitive inhibitor of myo-inositol transport by cultured mammalian cells. Chronic exposure of neuroblastoma cells to L-fucose causes a concentration-dependent decrease in myo-inositol content, accumulation, and incorporation into phosphoinositides. In these studies, L-fucose supplementation of culture medium was used to assess the effect of decreased myo-inositol metabolism and content on bradykinin-stimulated phosphatidylinositol synthesis and diacylglycerol production. Chronic exposure of cells to 30 mM L-fucose caused a sustained decrease in bradykinin-stimulated, but not basal, 3H-inositol phosphate release and 32P incorporation into phosphatidylinositol in cells incubated in serum-free, unsupplemented medium. In addition, 32P incorporation into phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate was not altered in L-fucose-conditioned cells. Acute exposure of cells to serum-free medium containing 30 mM L-fucose did not affect either basal or bradykinin-stimulated 32P incorporation into phosphatidylinositol. Basal diacylglycerol content was decreased by 20% in cells chronically exposed to 30 mM L-fucose, although analysis of the molecular species profile revealed no compositional change. Bradykinin stimulated diacylglycerol production in neuroblastoma cells by increasing the hydrolysis of both phosphoinositides and phosphatidylcholine. Bradykinin-stimulated production of total diacylglycerol was similar for control and L-fucose-conditioned cells. However, there was a decrease in the bradykinin-induced generation of the 1-stearoyl-2-arachidonoyl diacylglycerol molecular species in the cells chronically exposed to 30 mM L-fucose. This molecular species accounts for about 70% of the composition of phosphoinositides, but only 10% of phosphatidylcholine. The results suggest that a decrease in myo-inositol uptake results in diminished agonist-induced phosphatidylinositol synthesis and phosphoinositide hydrolysis in cultured neuroblastoma cells grown in L-fucose-containing medium.