Increase of junctional and background 16S (tailed, asymmetric) acetylcholinesterase during postnatal maturation of rat and mouse sternocleidomastoid muscle.

Abstract

Acetylcholinesterase (AChE) is found both in motor end-plate (MEP)-free and MEP-rich regions of rat or mouse muscle. We studied the developmental aspects of the localization of asymmetric 16S AChE in both regions of the sternocleidomastoid muscle, which has a well-defined zone of motor innervation. In the rat, the proportion of 16S AChE to total AChE increases in the MEP-rich region, and becomes significantly higher than in the MEP-free regions between the first and the second weeks after birth. In the mouse, at birth, the MEP-rich region already has a higher relative content in 16S AChE than the MEP-free regions. Total 16S AChE amounts increase during postnatal development, not only in the MEP-rich region but also in the MEP-free regions. Thus, 16S AChE is not eliminated from MEP-free regions during muscle maturation and growth. Two distinct pools of 16S AChE are distinguished in the muscles, both of which increase during postnatal development: junctional and background 16S AChE.