title: Insulin-associated changes in carnitine palmitoyltransferase in cultured neonatal rat cardiac myocytes.
abstract: Insulin increases the synthesis of mitochondrial proteins in the isolated perfused heart and total cell protein synthesis in neonatal cardiac myocytes. Since carnitine-dependent fatty acid oxidation is modulated by insulin in a variety of tissues, the effects of 1.7 microM insulin on the mitochondrial enzyme(s), carnitine palmitoyltransferase (malonyl-CoA-sensitive CPT-I and the matrix-facing CPT-II), were studied in neonatal rat cardiac myocytes cultured in the absence of serum. Following incubation in serum-free medium, there is a four-fold increase in the I50 of CPT-I for malonyl-CoA (3.8 microM) compared to cells cultured in serum-free medium to which insulin has been added (I50 = 0.8 microM). CPT-I activity in the insulin-supplemented, serum-free cultures is 57% higher (P < 0.002) than CPT-I activity in cells cultured in the absence of insulin; CPT-II activity is also significantly increased (P < 0.01) in the presence of insulin. Since CPT-II is an inner membrane protein, the CPT response to insulin may be coordinately regulated with other mitochondrial activities. Similar to CPT, cytochrome oxidase activity of cardiac myocytes in serum-free medium is increased 33% by insulin. Consistent with this finding, both CPT-II and cytochrome oxidase mRNA expression is elevated over control in the presence of insulin. CPT-II activity increases significantly only at very high insulin concentrations (1.7 microM), suggesting a role for insulin-like growth factor pathway. When myocytes are cultured in the presence of 1.7 microM insulin and then transferred to an insulin-free medium, subsequent addition of insulin does not stimulate uptake of deoxyglucose. These results suggest that the response of CPT to insulin is mediated by insulin-like growth factor activity and not by cellular glucose availability. The response of CPT to insulin does not appear to be mediated by the protein kinase C pathway since CPT-II activity is not reduced by the protein kinase C inhibitor, chelerythrine. Insulin significantly increases protein synthesis in the neonatal cardiac myocyte and in isolated mitochondria by increasing incorporation of labelled amino acid into total myocyte and/or mitochondrial protein. The degradation rate of radiolabelled protein in cardiac myocytes cultured in the presence of insulin is not different from that of insulin-deprived cells. The data suggest that insulin can affect the activity and expression of mitochondrial proteins, e.g., CPT, through the insulin-like growth factor-I pathway in neonatal cardiac myocytes.
authors.affiliation: University of Texas Health Science Center Medical School, Department of Pathology and Laboratory Medicine, Houston, USA.
authors.forename: E K
authors.initials: EK
authors.lastname: Hudson
authors.forename: M H
authors.initials: MH
authors.lastname: Liu
authors.forename: L M
authors.initials: LM
authors.lastname: Buja
authors.forename: J B
authors.initials: JB
authors.lastname: McMillin
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001692:Biological Transport / Q000187:drug effects; D002334:Carnitine O-Palmitoyltransferase / Q000096:biosynthesis / Q000378:metabolism*; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D015342:DNA Probes; D003847:Deoxyglucose / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008316:Malonyl Coenzyme A / Q000378:metabolism; D009206:Myocardium / Q000201:enzymology*; D012337:RNA, Ribosomal, 18S / Q000096:biosynthesis; D051381:Rats; D013379:Substrate Specificity; D013997:Time Factors
chemical_list: D016895:Culture Media, Serum-Free; D015342:DNA Probes; D007328:Insulin; D007527:Isoenzymes; D012337:RNA, Ribosomal, 18S; D008316:Malonyl Coenzyme A; D003847:Deoxyglucose; D003576:Electron Transport Complex IV; D002334:Carnitine O-Palmitoyltransferase