Lipoprotein lipase release from cardiac myocytes is increased by decavanadate but not insulin.
Streptozotocin-induced diabetes reduced cellular lipoprotein lipase (LPL) activity in cardiac myocytes from rat hearts and decreased the heparin-induced release of LPL into the medium. This effect of diabetes was rapidly reversed by in vivo treatment with insulin (5 U iv for 1 h); administration of insulin in vivo to control rats also increased heparin-releasable LPL activity. In contrast, in vitro addition of insulin to control and diabetic myocytes did not alter either cellular or heparin-releasable LPL activities. Insulin stimulated glucose oxidation and protein synthesis in control and diabetic myocytes. Decavanadate (0.05-1 mM) or vanadyl ion (0.5 mM) enhanced the release of LPL into the medium. Heparin- and decavanadate-induced release of LPL was not additive, and heparin pretreatment reduced the subsequent release of LPL by decavanadate. Decavanadate displaced LPL bound to heparin-Sepharose and increased LPL release into the perfusate of hearts. Therefore, decavanadate can mimic heparin in its effect on LPL. The absence of a direct in vitro effect of insulin on LPL in cardiac myocytes suggests that insulin may require some other in vivo factor or that diabetes-induced changes in LPL activity are secondary to some other metabolic factor.
Braun
J E
JE
Medical Research Council Signal Transduction Group, Faculty of Medicine, University of Calgary, Alberta, Canada.
Severson
D L
DL
D000818:Animals; D002469:Cell Separation; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology; D005947:Glucose / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D008071:Lipoprotein Lipase / Q000378:metabolism*; D008297:Male; D009206:Myocardium / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology; D010084:Oxidation-Reduction; D010477:Perfusion; D014176:Protein Biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D014638:Vanadates / Q000494:pharmacology*
D007328:Insulin; D014638:Vanadates; D006493:Heparin; D008071:Lipoprotein Lipase; D005947:Glucose