Acetylcholinesterase like that of skeletal muscle in smooth muscle reinnervated by a motor nerve [20]

SKELETAL muscles contain several molecular forms of acetylcholinesterase (AChE) characterised by different sedimentation coefficients^1-4. In rat muscle^1,2 (but not human³ and chicken⁵ muscle) the heavy form of AChE is exclusively present at the motor endplate regions. In contrast, the heavy form of AChE has not been detected in cat ⁶ or rat² smooth muscles. The endplate AChE of rat skeletal muscle is selectively detached by treatment with collagenase ^1,7, an enzyme which has been shown specifically to digest the collagen-like tail of the heavy form of AChE from several sources^8,9. The presence of endplate AChE is neurally regulated¹⁰, and there is evidence that this effect is partially mediated by muscle activity¹¹ and by a trophic factor conveyed by axoplasmic transport^12,13. Previous results from our laboratory have shown that reinnervation of the cat nictitating membrane smooth muscle by a motor nerve results in an increase of AChE activity¹⁴. We report here that collagenase treatment detaches active AChE from cat smooth muscle reinnervated by a cholinergic motor nerve, and that a new AChE form with a high sedimentation coefficient is induced in these muscles. Our results suggest that the presence of the motor nerve determines, in reinnervated smooth muscle, the appearance of an AChE similar to that found in skeletal muscle.