Fig. 7. Gradation between S₁ and S₂ muscle phenotypes identified through SDS-PAGE and western blotting, demonstrating the correlation among MHC, TnT and TnI isoforms. Predominantly S₂ muscle samples are on the left (lanes a,b), a predominantly S₁ sample is on the right (h), and samples following a gradation from S₂ to S₁ are in the middle (c-g) (a,b,h are single fibers, while c-g are fiber bundles). Myosin heavy chains (MHC) were identified by SDS-PAGE and silver staining. The S₂ MHC isoform has a lower electrophoretic mobility and is identified by a filled circle. The S₁ MHC has a higher mobility and is identified by an open circle. The four samples on the left (a-d) only possessed the S₂ MHC, the middle samples (e-g) had both S₁ and S₂ isoforms, and the last sample (h) possessed only the S₁ isoform. Troponin (Tn) T and I isoforms were identified by SDS-PAGE followed by western blotting. The TnT isoforms showed an orderly progression from TnT₁ (a,b) to both TnT_1,3 (c-g) to only TnT₃. The TnI isoforms showed a progression from TnI₂ (a,b) to TnI_2,3 (c-e), to TnI₃ (f-h). Various proportions of TnI₁ and TnI₄ were also observed in several of the samples (d,e,g,h).