SATELLITE CELLS IN SLOW AND FAST RAT MUSCLES DIFFER IN RESPECT TO ACETYLCHOLINESTERASE REGULATION MECHANISMS THEY CONVEY TO THEIR DESCENDANT MYOFIBERS DURING REGENERATION

The hypothesis of satellite cell diversity in slow and fast mammalian muscles was tested by examining acetylcholinesterase (AChE) regulation in muscles regenerating 1) under conditions of muscle disuse (tenotom y, leg immobilization) in which the pattern of neural stimulation is c hanged, and 2) after cross-transplantation when the regenerating muscl e develops under a foreign neural stimulation pattern. Soleus (SOL) an d extensor digitorum longus (EDL) muscles of the rat were allowed to r egenerate after ischemic-toxic injury either in their own sites or had been cross-transplanted to the site of the other muscle. Molecular fo rms of AChE in regenerating muscles were analyzed by velocity sediment ation in linear sucrose gradients. Neither tenotomy nor limb immobiliz ation significantly affected the characteristic pattern of AChE molecu lar forms in regenerating SOL muscles, suggesting that the neural stim ulation pattern is probably not decisive for its induction. During an early phase of regeneration, the general pattern of AChE molecular for ms in the cross-transplanted regenerating muscle was predominantly det ermined by the type of its muscle of origin, and much less by the inne rvating nerve which exerted only a modest modifying effect. However, a lkali-resistant myofibrillar ATPase activity on which the separation o f muscle fibers into type I and type II is based, was determined predo minantly by the motor nerve innervating the regenerating muscle. Matur e regenerated EDL muscles (13 weeks after injury) which had been inner vated by the SOL nerve became virtually indistinguishable from the SOL muscles in regard to their pattern of AChE molecular forms. However, AChE patterns of mature regenerated SOL muscles that had been innervat ed by the EDL nerve still displayed some features of the SOL pattern. In regard to AChE regulation, muscle satellite cells from slow or fast rat muscles convey to their descendant myotubes the information shift ing their initial development in the direction of either slow or fast muscle, respectively. The satellite cells in fast or slow muscles are, therefore, intrinsically different. Intrinsic information is expresse d mostly during an early phase of regeneration whereas later on the re gulatory influence of the motor nerve more or less predominates. (C) 1 994 Wiley-Liss, Inc.