Insulin-associated changes in carnitine palmitoyltransferase in cultured neonatal rat cardiac myocytes

J Mol Cell Cardiol. 1995 Jan;27(1):599-613. doi: 10.1016/s0022-2828(08)80054-5.


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.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Animals, Newborn
  • Biological Transport / drug effects
  • Carnitine O-Palmitoyltransferase / biosynthesis
  • Carnitine O-Palmitoyltransferase / metabolism*
  • Cells, Cultured
  • Culture Media, Serum-Free
  • DNA Probes
  • Deoxyglucose / metabolism
  • Electron Transport Complex IV / metabolism
  • Insulin / pharmacology*
  • Isoenzymes / metabolism
  • Kinetics
  • Malonyl Coenzyme A / metabolism
  • Myocardium / enzymology*
  • RNA, Ribosomal, 18S / biosynthesis
  • Rats
  • Substrate Specificity
  • Time Factors


  • Culture Media, Serum-Free
  • DNA Probes
  • Insulin
  • Isoenzymes
  • RNA, Ribosomal, 18S
  • Malonyl Coenzyme A
  • Deoxyglucose
  • Electron Transport Complex IV
  • Carnitine O-Palmitoyltransferase