1-oleoyl-2-acetylglycerol and Insulin-Resistance

Recent studies show that bioactive lipids alter intracellular Ca(2+) handling of cardiac cells differently in normal and insulin-resistant cardiomyocytes. In the present study we measured non-selective cation currents (NSCC) focusing on the interaction between insulin, the bioactive lipid diacylglycerol (DAG) and canonical transient receptor potential 3 (TRPC3) channels.. Whole cell patch-clamp was used to measure NSCC in ventricular cardiomyocytes isolated from adult wild-type (WT) and insulin resistant, obese ob/ob mice. Western blot, immunoprecipitation and immunofluorescence staining were used to study the concentration and cellular distribution of TRPC3 channels.. Application of the membrane permeable DAG analogue (OAG, 30 microM) induced an NSCC, which was approximately 40% smaller in ob/ob than in WT cardiomyocytes. Insulin induced a small NSCC with similar amplitude in ob/ob and WT cells. Pretreatment with insulin (60 nM) increased the OAG-induced NSCC in WT (by approximately 50%) but not in ob/ob cells. OAG-induced currents were inhibited by adding anti-TRPC3 antibodies to the patch pipette solution. The expression of TRPC3 was lower in ob/ob than in WT cardiomyocytes. TRPC3 was detected in glucose transporter 4 (GLUT4) immunoprecipitates. Insulin exposure resulted in a translocation of TRPC3 to the plasma membrane in WT but not in ob/ob cardiomyocytes.. Insulin-resistant ob/ob cardiomyocytes showed decreases in DAG-mediated NSCC, which were accompanied by decreased TRPC3 expression and defective insulin-mediated trafficking of this protein.

Topics: Animals; Biological Transport; Blotting, Western; Cell Membrane; Cells, Cultured; Diglycerides; Glucose Transporter Type 4; Immunoprecipitation; Insulin; Insulin Resistance; Ion Channels; Male; Mice; Mice, Inbred C57BL; Microscopy, Confocal; Myocytes, Cardiac; Obesity; Patch-Clamp Techniques; TRPC Cation Channels

Insulin exposure stimulates an increase in glycerol-3-phosphate dehydrogenase (G3PDH) activity in isolated human lymphocytes that correlates to an increase in G3PDH mRNA and requires new protein synthesis. Synthetic diacylglycerol or phorbol ester can mimic the effect of insulin on G3PDH activity, suggesting that protein kinase C may be involved in regulation of G3PDH levels. In addition, lithium chloride, an inositol phosphate phosphatase inhibitor, and calcium uptake inhibitors can abolish insulin stimulation of G3PDH activity. For obese subjects in whom insulin resistance in vitro can be demonstrated, the extent of insulin stimulation of G3PDH activity is decreased compared to normal weight individuals, and treatment by a very low calorie diet restores insulin stimulation of G3PDH activity. Thus, insulin stimulation of G3PDH activity is dependent upon the metabolic state of the subject from whom the cells are obtained.

Topics: Diet, Reducing; Diglycerides; Female; Gene Expression; Glycerolphosphate Dehydrogenase; Humans; Insulin; Insulin Resistance; Kinetics; Male; Middle Aged; Obesity; Reference Values; RNA Probes; RNA, Messenger; Tetradecanoylphorbol Acetate; Time Factors; Weight Loss