In vitro primary satellite cell growth and differentiation within litters of pigs

Postnatal muscle growth is dependent on satellite cell (SC) proliferation, differentiation and fusion to increase the DNA content of existing muscle fibres and thereby the capacity to synthesize protein. The purpose of the present study was to examine the ability of isolated SCs from low, medium and high weaning weight litter mates of pigs to proliferate and differentiate, and to affect protein synthesis and degradation after fusion into myotubes. At 6 weeks of age, SCs from the lowest weight (LW), medium weight (MW) and highest weight (HW) female pigs within eight litters were isolated. Thereby, eight cultures of SCs were established for each of the three weight groups within litter, representing three groups of SCs from pigs exhibiting differences in postnatal muscle growth performance. Proliferation was estimated as the number of viable cells at different time points after seeding. SC differentiation was evaluated by measuring the acitivity of the muscle-specific enzyme, creatine phosphokinase, and protein synthesis and degradation were measured by incorporation and release of H-3-tyrosine, respectively. A tendency towards a difference in proliferation between SC cultures was found (P=0.09). This was evident as the number of viable cells at day 3 was lower in cultures from LW pigs than from HW (P<0.05) and MW (P<0.01) pigs. Differentiation was significantly different between cultures (P<0.05). There was a significant difference between LW and MW cultures at 72h (P<0.05), and a tendency towards a difference between LW and HW cultures at 45h (P=0.07). Protein synthesis per mu g protein or per mu g DNA did not differ among SC cultures from L W, MW and HW pigs. Neither did protein degradation rate differ significantly among SC cultures from LW, MW and HW pigs. Overall, the results show that SCs from LW pigs seem to proliferate and differentiate at a slower rate than SCs from MW and HW pigs. The results found in this study show no difference in the ability of SCs to affect protein synthesis or degradation between M from litter mates exhibiting different growth rates in vivo.