Time-dependent effects of insulin on lipid synthesis in cultured fetal rat hepatocytes: a comparison between lipogenesis and glycogenesis.

The lipogenic effect of insulin was studied in 18-day-old fetal rat hepatocytes after 2 to 3 days of culture in the presence of glucocorticoids when an acute stimulatory effect of insulin on glycogenesis was present. The rate of [1-14C]-acetate incorporation into lipids measured for 4 hours was much higher than with [U-14C]-glucose (30 v 3.8 nmol/h/mg protein).

Compared roles of glucose, galactose and fructose as glycogen precursors during the acute response to insulin in cultured rat foetal hepatocytes.

1. The efficiency of the contribution of hexoses to basal- and stimulated-glycogenesis, when studied in cultured 18 day-old rat foetal hepatocytes in the presence of glucose, was as follows: galactose greater than glucose greater than fructose. 2.

Cholesterol depletion affects the Ca2+ influx but not the Ca2+ pump in human erythrocytes.

Control and cholesterol-depleted human erythrocytes were loaded with permeant Ca2+ chelators (Benz2-AM or Quin2-AM) in order to increase their exchangeable Ca2+ pool and to measure both Ca2+ fluxes and [Ca]i (free cytoplasmic calcium concentration). The fluxes were independent of the concentration and of the nature of the intracellular chelator. The ATP content was not decreased by more than 50% under our experimental conditions.

Phosphoinositide reorganization in human erythrocyte membrane upon cholesterol depletion.

The effect of cholesterol depletion on the activity of phosphatidylinositol/phosphatidylinositol 4-phosphate and diacylglycerol kinases and polyphosphoinositide phosphodiesterase has been studied in isolated membranes of human normal and cholesterol-depleted erythrocytes. Polyphosphoinositide synthesis (phosphatidylinositol/phosphatidylinositol 4-phosphate kinase activities) were found to depend on the permeability and sidedness characteristics of the membrane vesicles, which could limit the accessibility of ATP for the enzymes. When measured under proper conditions, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate synthesis were decreased in cholesterol-depleted membranes as compared with control membranes.

Changes in morphology and in polyphosphoinositide turnover of human erythrocytes after cholesterol depletion.

Human erythrocytes were cholesterol-depleted (5-25%) by incubation with phosphatidylcholine vesicles in media containing Ca2+ at different concentrations (0, 28 nM, 5 microM or 1 mM). After removal of the vesicles, the cells were reincubated with [32P]phosphate in the same media. Control (incubated in buffer alone) and cholesterol-maintained erythrocytes (incubated with cholesterol/phosphatidylcholine vesicles) were treated similarly.