Résumé
In the skeletal muscles of vertebrates, the level of acetyl-cholinesterase (AChE, EC 3.1.1.7.) may be either decreased (in rat) or increased (in chicken1 and rabbit2,3) after denervation. This enzyme is very polymorphic, however, presenting molecular forms which differ in their cellular localization and physiological regulation. The different AChE molecules may be classified as globular forms (monomers G1, dimers G2 and tetramers G4) and asymmetric or collagen-tailed forms (containing one, two or three tetramers: A4, A8 and A12)4. The distribution of the collagen-tailed and globular forms along the muscle fibres varies according to the animal species and physiological state: in normal adult rat muscle, the A12 form, which represents the major collagen-tailed form, is localized exclusively in the endplate region4–6, whereas in rat embryo7 and human muscle8 this form is distributed over the entire muscle fibre. The presence of collagen-tailed AChE has, however, been considered as an indicator of neuromuscular interactions because its appearance during embryogenesis coincides with the establishment of neuromuscular contacts6,9 and because, after denervation, the A12 form disappears from rat5,6 and chicken10,11 muscles. Here we report that this form in fact increases markedly in a slow twitch oxidative muscle of the rabbit after denervation. The regulation of asymmetric—and particularly A12—forms of AChE thus depends dramatically on the species and on the nature of skeletal muscle.