title: [Effects of insulin on proteolysis of cultured rabbit skeletal muscular myotubes in vitro].
abstract: OBJECTIVE
  To study the effects of insulin on the proteolysis of cultured rabbit skeletal muscular myotubes in vitro, and their possible mechanisms.
  
  
  METHODS
  Muscles of lower limbs of juvenile rabbits were isolated for tissue-block culture. After passage, myoblasts were formed and fused into myotubes. Then the protein in myotubes was radiolabelled with L-[ 3,5-3H] tyrosine. The myotubes were cultured in DMEM medium containing 100 nmol/L insulin (n = 24, group B) , 100 nmol/L dexamethasone (n = 24, group C) , 100 nmol/L insulin and 100 nmol/L dexamethasone (n = 24, group D) , no insulin or dexamethasone (n =24, group A), respectively. Twenty-four hours after culture, the L-[3,5-3H] tyrosine content in culture medium and cells were determined, and the degradation rates of protein were calculated. The mRNA expressions of ubiquitin and protease C2 subunit were determined by Northern blot.
  
  
  RESULTS
  The degradation rates of myotube protein in group A(0. 38+/-0.04) was obviously lower than that in group C (0.50+/-0.03, P <0.01), but it was obviously higher than that in group B(0. 35+/-0.03, P <0.05). Though the degradation rates of myotube protein in group D (0.41+/-0. 03) was evidently lower than that in group C ( P < 0.01) , it was still higher than that in group A( P < 0.05 ). The mRNA expressions of ubiquitin and protease C2 subunit in group A ( the scale: 2. 4 kb ubiquitin was 0. 82+/-0. 15, 1. 2 kb ubiquitin was 0. 60+/-0. 10, C2 subunit was 0. 75+/-0. 16) was obviously lower than that in group C ( the scale: 2.4 kb ubiquitin was 2. 15+/-0. 23, 1.2 kb ubiquitin was 1.50+/-0. 14,C2 subunit was 1.50+/-0. 13 , P <0. 01) , but it in group D was lower than that in group C (the scale: 2. 4 kb ubiquitin was 1. 25+/-0. 17, 1. 2 kb ubiquitin was 0. 85+/-0. 09, C2 subunit was 0. 90+/-0. 15, P <0. 01) , and it was similar to that in group B (the scale: 2.4 kb ubiquitin was 0. 85+/-0.07, 1.2 kb ubiquitin was 0. 65+/- 0. 12, C2 subunit was 0. 76 +/-0. 09, P > 0. 05).
  
  
  CONCLUSIONS
  The effects of insulin on the activity of ubiquitin-proteasome pathway and the proteolytic rate in normal myotubes were relatively weak. However, insulin can significantly inhibit the effects of dexamethasone on the gene expressions of ubiquitin system and the proteolytic rate in myotubes, but the mechanism needs further research.
authors.affiliation: Burn Institute, the First Affiliated Hospital to General Hospital of PLA, Beijing 100037, PR China.
authors.forename: Chuan-an
authors.initials: CA
authors.lastname: Shen
authors.forename: Jia-ke
authors.initials: JK
authors.lastname: Chai
authors.forename: Zhi-yong
authors.initials: ZY
authors.lastname: Sheng
authors.forename: Hong-ming
authors.initials: HM
authors.lastname: Yang
authors.forename: Hui-man
authors.initials: HM
authors.lastname: Yin
authors.forename: Rui
authors.initials: R
authors.lastname: Feng
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism; D011817:Rabbits; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D007328:Insulin; D009124:Muscle Proteins; D025801:Ubiquitin