REDISTRIBUTION OF CELL-MEMBRANE PROBES FOLLOWING CONTRACTION-INDUCED INJURY OF MOUSE SOLEUS MUSCLE

Our aim was to study how mouse skeletal muscle membranes are altered b y eccentric and isometric contractions. A fluorescent dialkyl carbocya nine dye (DiOC(18)(3)) was used to label muscle membranes, and the mem branes accessible to the dye were observed by confocal laser scanning microscopy. Experiments were done on normal mouse soleus muscles and s oleus muscles injured by 20 eccentric or 20 isometric contractions. Lo ngitudinal optical sections of control muscle fibers revealed DiOC(18) (3) staining of the plasmalemma and regularly spaced transverse bands corresponding in location to the T-tubular system. Transverse optical sections showed an extensive reticular network with the DiOC(18)(3) st aining. Injured muscle fibers showed distinctively different staining patterns in both longitudinal and transverse optical sections. Longitu dinal optical sections of the injured fibers revealed staining in a lo ngitudinally-oriented pattern. No correlations were found between the abnormal DiOC(18)(3) staining and the reductions in maximal isometric tetanic force or release of lactate dehydrogenase (P greater than or e qual to 0.32). Additionally, no difference in the extent of abnormal s taining was found between muscles performing eccentric contractions an d those performing the less damaging isometric contractions. However, many fibers in muscles injured by eccentric contractions showed swolle n regions with marked loss of membrane integrity and an elevated free cytosolic calcium concentration as observed in Fluo-3 images; In concl usion, a loss of cell membrane integrity results from contractile acti vity, enabling DiOC(18)(3) staining of internal membranes. The resulti ng staining pattern is striking and fibers with damaged cell membranes are easily distinguished from uninjured ones.