Intracellular acetylcholinesterase of adult rat myofibers is more concentrated in endplate than non-endplate regions

✍ Scribed by Dr. J. A. Donoso; J. R. Stiles; H. L. Fernandez

• Publisher: John Wiley and Sons
• Year: 1987
• Tongue: English
• Weight: 801 KB
• Volume: 17
• Category: Article
• ISSN: 0360-4012
• DOI: 10.1002/jnr.490170209

✦ Synopsis

The intracellular distribution of acetylcholinesterase Massoulie et al, 19801. Such issues as the functional (AChE) was determined in adult rat anterior gracilis interrelationship, physiological significance, and metamuscles. Echothiophate iodide (ECHO), a water-solbolic regulation of the various AChE forms require a uble cholinesterase inhibitor, was applied to muscles detailed understanding of the enzyme's subcellular distriin situ to eliminate extracellular and/or extracellularly bution. Predictably, the determination of the amount and oriented enzyme. Control and ECHO-treated muscles molecular form makeup of that AChE activity existing in were either cut into l-mm segments and assayed for the synaptic cleft or possessing catalytic sites oriented AChE activity or cytochemically stained for AChE. toward the cleft ("endplate-specific activity") has been a Subsequent analysis by light and electron microscopy primary concern. Although the presence of AChE within showed that the AChE stain inside myofibers was rat myofibers has long been known [Giacobini and highly localized and clearly visible only in the zone Holmstedt, 19601, an explicit biochemical demonstration immediately underlying the point of nerve-muscle of increased amounts in sub-endplate sarcoplasm has not contact. Biochemical assay of muscle segments showed been forthcoming. intracellular AChE to be most highly concentrated in At present the only means with which to distinguish regions containing large numbers of endplates (apin situ intra-versus extracellular AChE molecular form proximately twice the activity of endplate-free areas). activities is to selectively solubilize vulnerable extracel-Since such "endplate-rich" segments are in fact Mar forms via mild proteolytic digestion, or alternately mostly extra-synaptic tissue, we conclude that intrato inhibit intra-or extracellular activity through the use cellular AChE of adult rat gracilis myofibers, alof a pharmacologic paradigm involving lipid and/or though present along the length of the cell, is more water-soluble cholinesterase (ChE) inhibitors [Fernandez than two times as concentrated in sub-synaptic areas et al, 1984; Younkin et al, 19821. In addition, we have as compared to extra-synaptic areas. This result must previously performed ultrastructural analysis of tissues be carefully considered when attempting to identify exposed to such inhibitor treatments and subsequently "endplate-specific" AChJ3 activity of mammalian cytochemically stained for-specific AChE activity in or- muscle, and further points to the importance of neural der to confirm visually the validity of the pharmacologic influences on AChE metabolism/regulation.

techniques [Donoso and Fernandez, 19851. In agreement with other cytochemical studies [Brzin et al, 1981; ache distribution Tennyson et al, 19771 such work discussed the apparent existence of increased AChE concentrations within intracellular subsynaptic regions of adult skeletal muscle when