Passive Viscoelastic Properties of Costameres in EDL Skeletal Muscle in Normal and Dystrophin Null Mice

摘要

Costameres at the sarcolemmal skeletal myofibers transmit the lateral force generatedby myofibrils from them to the extracellular matrix. We used an elastimeter method by whichsucking pressure is applied through a micropipette to the surface membrane of single micemyofibers of the Extensor digitorum longus to measure the viscoelasticity of the sarcolemma-costamere complex as a function of sarcomere length (SL). Constant suction pressure applied tothe sarcolemma generated a sarcolemmal-costamere-myofibril bleb of variable height dependingon the sucking pressure and SL. It took some time for the bleb to reach a stable height afterapplying the pressure. This time delay indicates that the sarcolemma-costamere-myofibrilsystem acts as a viscoelastic system. We undertook the present experiments to measure theheight stabilization time of the bleb at different sarcomere lengths from which we estimated theviscoelastic parameters of the system. The time course of the bleb formation was biphasic andreached a plateau between 3.5 to 1.3 and 4.9 to 3.5 min for normal and dystrophic micerespectively depending on SL of 3.0 to 5.6 μm. Based on a Maxwell-Voigt system we found theviscoelastic parameters such as viscosity, friction coefficient and the costameres (k) andsarcolemma (k_1) elasticity constants.