Post-operative effects on insulin resistance and specific tension of single human skeletal muscle fibres

Surgery and accidental trauma are associated with a transient period of ins ulin resistance, substrate catabolism and muscle weakness. In the present s tudy, we evaluated the changes in the force-generating capacity of chemical ly skinned single muscle fibres following abdominal surgery. Biopsies of th e m. vastus lateralis were obtained in three patients I day before and 3 or 6 days after surgery. Part of the biopsy was frozen for histochemical anal ysis of the fibre cross-sectional area (FCSA) and myofibrillar protein cont ent, and another part was used for single-fibre contractile measurements. A ll patients developed insulin resistance following surgery. The maximum vel ocity of unloaded shortening of single muscle fibres did not change followi ng surgery. The FCSA did not decrease after surgery, as determined either f rom histochemical sections or from single fibres measured at a fixed sarcom ere length of 2.76+/-0.09 mu m (mean +/- S.D.). Further, the force-generati ng capacity of the single fibres, measured as maximal Ca2+-activated force (P-0)or as P-0 normalized to FCSA (specific tension), remained unchanged, a s did the myofibrillar protein content of the muscle. In conclusion, the mu scle weakness associated with post-operative insulin resistance is not rela ted to a decreased specific tension or a loss of myofibrillar proteins. Oth er potential cellular mechanisms underlying post-operative weakness are dis cussed.