REGULATION OF MUSCLE-CELL PROLIFERATION BY EXTRACTS FROM CRUSHED MUSCLE

Cell culture studies were conducted to determine whether myotrophic fa ctors were released from mature murine or bovine muscle following a cr ush injury. Murine crushed muscle extract (mCME) was added to C2 muscl e (satellite) cell cultures at concentrations of 0, 50, 100, 200, and 400 mu g of total protein/mL. Bovine crushed muscle extract (bCME) was added at concentrations of 0, 100, 200, 400, and 500 mu g/mL. Murine CME and bCME at each concentration caused an increase (P < .01) in [H- 3]TdR incorporation into muscle cells compared to control cultures. Th e saturating concentrations (P < .01) of CME in the presence of 2% FBS were approximately 200 and 400 mu g/mL for murine and bovine extracts , respectively. Murine CME or bCME acted in an additive fashion with i ndependent, saturating concentrations of the insulin-like growth facto rs (IGF-I and IGF-II), basic fibroblast growth factor (bFGF), and tran sforming growth factor-beta (TGF-beta) to increase (P < .01) C2 muscle cell proliferation. Subsequently, in separate experiments, mCME or bC ME acted additively with a combination of all growth factors to increa se (P < .01) cell proliferation. Combining mCME and bCME not (P > .05) additive to that elicited by either CME alone. These results suggest that myotrophic factors are released following injury in mature skelet al muscle, and they are not species-specific.