Effects of insulin and guanosine 5'-[gamma-thio]triphosphate on fatty acid synthesis and lipolysis within electropermeabilized fat-cells.
1. Exposure to electric fields ('electroporation') has been used to investigate the mechanism of the action of insulin on the regulation of fatty acid synthesis and lipolysis in isolated rat fat-cells. 2. Exposure of the cells to electric fields (six pulses at 2 or 3 kV/cm) permitted the uptake of a number of low-Mr molecules normally excluded from cells, including sucrose (Mr 342), EDTA (Mr 394) and propidium iodide (Mr 668). At least 90% of the cells were found to be permeable to these species. 3. Insulin stimulated the synthesis of fatty acids in electroporated (2 kV/cm) cells to a similar extent (0.68 +/- 0.19 to 6.7 +/- 0.7 micrograms-atoms of glucose carbon/h per g, or 3.3 +/- 0.6 to 11.2 +/- 1.6 micrograms-atoms of H2O hydrogen/h per g) to that observed in non-electroporated cells. Guanosine 5'-[gamma-thio]triphosphate (GTP[S]; 0.5 mM) also stimulated fatty acid synthesis (2-fold) and flux of glucose carbon into triacylglycerol glycerol (3-fold) in these cells, but had no effect on these parameters in non-electroporated cells. 4. Lipolysis in the electroporated cells was stimulated by isoprenaline and also by GTP[S], but only the effects of isoprenaline were inhibited by insulin. 5. Exposure to a higher field strength (3 kV/cm) gave results qualitatively similar to those described above, although the effects of insulin and isoprenaline were diminished. 6. These studies provide evidence against a role for changes in Ca2+, and probably also Na+, K+ or Mg2+, in insulin action on fat-cells, but may support a role for GTP-binding proteins.
Rutter
G A
GA
Department of Biochemistry, School of Medical Sciences, University of Bristol, UK.
Denton
R M
RM
D000273:Adipose Tissue / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002463:Cell Membrane Permeability; D004558:Electric Stimulation; D005227:Fatty Acids / Q000096:biosynthesis*; D005947:Glucose / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000502:physiology*; D007328:Insulin / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008066:Lipolysis / Q000502:physiology*; D008297:Male; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014280:Triglycerides / Q000378:metabolism
D005227:Fatty Acids; D007328:Insulin; D014280:Triglycerides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D010727:Phosphoric Diester Hydrolases; D005947:Glucose; D007545:Isoproterenol