SARCOLEMMAL DISRUPTION IN RELOADED ATROPHIC SKELETAL-MUSCLE

The purpose of this study was to determine whether reloading of atroph ied skeletal muscle after 28 days of hind-limb unloading (HU) would pr oduce significant sarcolemmal membrane disruption before frank necrosi s. Soleus and plantaris muscles were atrophied by HU. Adult female Wis tar rats (N = 13) were killed at 28 days of unloading and 4 and 7 days of reloading after HU. Rat serum albumin was used as a marker for mus cle fiber disruption. Dark intracellular staining with horseradish per oxidase-conjugated anti-rat serum albumin antibody was interpreted as evidence of membrane rupture. There was a significantly different time course of disruption between plantaris and soleus muscles, with a neg ative correlation between cell size and occurrence of disruption. Four teen percent of plantaris fibers were wounded after HU, peaking at day 4 of reloading (20% of cross-sectional area). Soleus demonstrated dis ruption only on reloading peaking in severity at clay 7 (14% of fibers ). It was demonstrated that sarcolemmal disruption due to atrophy and reloading does not always progress to necrosis and degeneration by the 7th day of recovery.