THE DYSTROPHIN MEDIATED LINK BETWEEN CYTOSKELETON AND EXTRACELLULAR MATRIX : BIOPHYSICAL STUDIES ON IONIC CONDUCTANCES AND MECHANICAL PROPERTIES OF THE SARCOLEMMA

Muscular dystrophies seem to originate from mutation of proteins belonging to large complexes spanning the membrane from the cytoskeleton to the extracellular matrix. Such complexes might work as mechanical stabilizers of the sarcolemma as well as anchoring sites for ionic channels and their regulatory proteins. We focus our investigation on four of these proteins whose deficiency has been shown to cause muscle dystrophy. Collagen VI, laminin-2, dystrophin and integrin 7B are thought to be crucial part of a unique large complex able to transmit force through the sarcolemma and to localize and modulate the AchR and voltage-gated channels. We plan to investigate both mechanical and electrophysiological properties of skeletal muscle fibers from wild type and knock out mice in order to better understand the role of these four proteins in the pathogenesis of muscular dystrophies. We will characterize the resistence of the sarcolemma to mechanical stretch, the transversal force transmission between adjacent muscle fibres and the mechanical properties of the muscle-tendon junction. We will investigate using conventional electrophysiological methods (single and two micro-electrode intracellular recording) the neuro-muscular transmission, the action potentials features and several ionic conductances of the sarcolemma. Besides standard techniques we will adopt a new biotechnological approach particularly suitable to investigate ionic channels localization and modulation as a function of their interactions with extracellular matrix molecules: the transistor recording technique. This technique will be applied for the first time to muscle fibres and seems to be particularly promising as it specifically allows the determination of ionic conductances in relation with binding of sarcolemma to ECM.