Combined effects of glucocorticoids and electromechanical activity on the acetylcholinesterase expression in the fast rat muscle

Protein synthesis is impaired in the glucocorticoid (GC)-treated fast mamma lian muscle. Electromechanical activity was reported to alleviate this effe ct. Acetylcholinesterase (AChE; EC 3.1.1.7) synthesis in the skeletal muscl e is regulated by both, GCs and electromechanical activity. In light of the above reports, one would expect that electrical stimulation will prevent G C-mediated fall of AChE synthesis in the muscle. On the other hand, a subst antial body of evidence suggests that electromechanical activity exerts its effect at the AChE mRNA level, while GCs most probably act at the translat ional or early posttranslational level. Different levels of action would be more consistent with the independent and therefore additive influences of the two regulatory factors. In order to ascertain whether glucocorticoid an d electromechanical effects interact in the control of AChE activity, we co mpared the effects of GCs on normal, nonstimulated fast rat skeletal muscle , with those of GC-treated and simultaneously electrically stimulated (toni c pattern, 10 Hz) muscle. Untreated and stimulated-only muscles were used a s respective controls. The effects on the fast extensor digitorum longus mu scle and slow soleus muscle, treated similarly were compared. As expected, chronic GC treatment and electrical stimulation of fast rat muscles with sl ow activity patterns both downregulated AChE activity. However, no addition al decrease in AChE activity was observed, if stimulated fast muscle was si multaneously treated with GCs, suggesting that slow pattern of electromecha nical activity prevents GC-mediated downregulation of AChE. The most plausi ble explanation of this observation is, that muscle activity blocks express ion of some generally acting factors, which are induced by GCs and are resp onsible for the impaired synthesis of several proteins including AChE. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.