Role of patellar tendon on the population of muscle fiber types and the contractile properties of single glycerinated muscle fibers in quadriceps muscles of rats.

Abstract

The role of the patellar tendon (PT) in the contractile properties of quadriceps muscle was investigated. After PT resection (partial or complete), PT reconstruction, or a sham operation, rats were forced to run on a rodent treadmill. The histochemical and mechanical characteristics of the vastus medialis (VM) and vastus lateralis (VL) muscles were examined 2, 4, and 8 weeks after treatment. There were no significant changes in either fiber type population or the contractile properties of glycerinated single muscle fibers from VM and VL 2 and 4 weeks after partial PT resection. Complete PT resection caused a decrease in the population of type I fibers in VM, while the running training after PT reconstruction increased the population of type I fibers in VM. For both the PT resection and PT reconstruction groups, the Hill coefficient, an indicator of the Ca2+ sensitivity of myofilaments, was calculated from the pCa-tension relationship of glycerinated single muscle fibers. In the PT reconstruction group, the Hill values for fibers isolated from VM were significantly decreased by running training, but the Hill values for VL were not. The effect of running training on the Ca2+ sensitivity of myofilaments in muscle fibers with PT reconstruction was different from that in muscle fibers without PT treatment. Both resection and partial resection of the PT in this animal model had heterogeneous effects on the contractile properties of quadriceps muscles; we presume that, clinically, we must give careful consideration to PT treatment.