Contractile properties of transplanted extensor digitorum longus muscles of cats.

Following autologous transplantation of whole extensor digitorum longus (EDL) muscles of cats into the EDL site, we investigated the degree and time course of restoration of contractile properties of autografts toward control values. Isometric and isotonic contractile properties of 66 autografted EDL muscles were measured in situ from 40 to 440 days following transplantation. The control value for maximum tetanus tension (P0) was 27 N. The mean P0 for the autografts increased from 2% of control 40 days after transplantation to 26% 440 days after transplantation. When P0 was normalized per square centimeter of muscle fiber cross-sectional area, no significant difference was observed between the P0 of autografts (28 N/cm2) and controls. Compared to controls, autografts 40-179 days following transplantation had slower time to peak twitch tensions, half-relaxation times, and maximum velocities of shortening and smaller twitch-tetanus tension ratios. Between 180 and 440 days after transplantation, values for autografts approached control values. Autografts fatigued more than twice as rapidly as controls.