Influence of leucine on protein metabolism of chicken embryo myoblasts is modulated by varying serum concentrations in the medium

The influence of varying leucine and fetal calf serum (FCS) concentrations in the culture medium on protein synthesis and degradation of chicken embryo myoblasts was examined. Medium199 contained 0, 1, 2, 5 or 10% FCS and 457 (original concentration of leucine in Medium 199), 2287 or 4574 micromol leucine/l. Protein synthesis was measured by incorporation of sup(3)H- phenylalanine. Protein degradation was measured by release of sup(3)H-phenylalanine once incorporated into myoblasts. There was an interaction between leucine and FCS concentrations on muscle protein synthesis. When FCS was not included in the medium, myoblast protein synthesis was increased with an increment of leucine concentration. At more than 5% of FCS, myoblast protein synthesis decreased by elevating leucine levels in the medium. Response surface of protein synthesis to varying leucine and FCS concentrations was calculated as follows: Protein synthesis (dpm)=1317.5+495.7X-29.3X**2+40.9Y-19.9XY+1.4X**2Y, where X is FCS concentration (%), and Y is leucine concentration (x 457.4 micromol/l). FCS concentration not interacting with the effect of varying leucine concentrations on protein synthesis was calculated to be 2.49%. No interaction between leucine and FCS concentrations on muscle protein degradation was observed. The effects of varying FCS and leucine levels on myoblast protein degradation showed quadratic response. When FCS increased from 0 to 7.25%, protein degradation dramatically decreased. However, when FCS increased from 7.25 to 10%, protein degradation tended to increase. The most effective leucine concentration suppressing protein degradation was calculated to be 2751 micromol/l. Thus, the influence of leucine on protein metabolism of chicken embryo myoblasts is modulated by varying serum concentrations in the medium.