Figure 9. Muscle. IHC analysis to detect cells expressing p16 (A) or p21 (B) in skeletal muscle of Young, Middle-aged, and Old donors. IHC analysis to detect cells expressing p16 (C) or p21 (D) in cardiac muscle of Young, Middle-aged, and Old donors. These proteins were undetectable in these muscle biopsies (5 cores per organ and age group).