The relative MHC isoform content was determined using SDS-PAGE as developed by Talmadge and Roy (1993) and adapted by Kohn et al. (2007c). Briefly, a volume of sample was loaded on 7% polyacrylamide gels containing 30% glycerol and run in the cold for 24 h, first at constant 70 V for 4 h, followed by 20 h at 275 V. Gels were subsequently silver stained, scanned and analyzed using the Un-Scan-It (Silk Scientific Corporation) software package. The protocol successfully separated the isoforms into three bands for human and lion skeletal muscles, whereas four bands were separated for that of caracal and rat