THE USE OF FLUORESCENT DEXTRANS AS A MARKER OF SARCOLEMMAL INJURY

We investigated the use of intravenously injected fluorescent dextran molecules (FDx) as a histological marker of sarcolemmal injury. Using fluorescent microscopy, uptake of FDx (average MW 10 kD) was assessed in sections of quadriceps muscles from three models: 1) normal (C57BL/ 10SnJ) mice, 2) normal mice run downhill (0, 3, and 7 days post exerci se), and 3) non-exercised mdx (dystrophin-deficient) mice. These were compared to serial sections stained with hematoxylin and eosin (H&E). In control muscles, strong fluorescence was seen between fibers (inter cellular). Intracellular FDx was observed within cells of the quadrice ps from normal mice run downhill at days 0 and 3 post exercise, but no t at day 7. On H&E staining, muscle pathology was not observed until d ay 3, with regeneration by day 7. Intracellular FDx was also observed within mdx muscles, particularly in fibers that appeared pre-necrotic on H&E stained sections. FDx appears to be useful as a histological ma rker of changes in sarcolemmal integrity associated with muscle injury from eccentric exercise or muscle disease.