Abstract
Electrical stimulation of neonatal rat cardiac myocytes in culture produces increases in myocyte size (hypertrophy) and organization of actin into myofibrillar arrays. The maturation of the cells is associated with enhanced contractile parameters and cellular calcium content. The numbers and intensity of cellular mitochondrial profiles increase, as measured by scanning laser confocal microscopy. Consistent with the hypertrophic response is increased cellular content of beta-myosin heavy chain and cytochrome oxidase subunit Va messages, as well as increases in cytochrome oxidase activity in the stimulated cardiac myocytes. Myocyte contractile capacity is associated with increased expression of the muscle carnitine palmitoyltransferase (CPT-I) isoform as measured by Northern analysis, immunoblotting, and altered sensitivity of CPT-I activity to malonyl-CoA in the stimulated cells. The data suggest that a switch from the liver isoform of CPT-I, prominent in the neonatal rat heart, to the muscle CPT-I which predominates in adult rat heart, takes place in the neonatal cardiac myocytes over the same time period as the hypertrophic-mediated changes in myofibrillar assembly and increased contractile activity.
Highlights
Tein content and expression and their role in ventricular remodelling have been extensively studied in cultured neonatal rat cardiac myocytes, the role of contractile stimulation of cardiac myocytes in the nuclear transcription of mitochondrialspecific proteins has not been described
The growth related expression of mitochondrial protein and of the heart isoforms of carnitine palmitoyltransferase-I (CPT-I) was investigated in this model of electrical stimulation where hypertrophic growth and maturation of the cardiac myocyte occur after prolonged increases in mechanical activity
After 72 h of stimulation, the mRNA content of the liver isoform appears to decrease in the cardiac myocytes, whereas the mRNA content of the muscle isoform was increased in the stimulated cells (Fig. 4)
Summary
Neonatal (1–3 day old) cardiac myocytes were isolated and plated in 12-well dishes in Dulbecco’s modified Eagle’s medium, supplemented with 10% Hyclone calf serum at a plating density of 4 ϫ 105 cells/21 cm, as described previously by this laboratory [16]. After 24 h, the serumcontaining medium was removed and the cells were washed and subsequently maintained for 72 h in Dulbecco’s modified Eagle’s medium in the absence of serum, containing 1% bovine serum albumin The medium bathing the control and stimulated cells was changed after 48 h to fresh Dulbecco’s modified Eagle’s medium ϩ 1% bovine serum albumin
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