ISSN:
1573-6830
Keywords:
acetylcholinesterase
;
depolarization
;
intracellular Ca2+
;
calmodulin
;
chick embryonic muscle
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary 1. Acetylcholinesterase (AcChoE; EC 3.1.1.7) exists in several molecular forms that may be anchored to cell membranes or associated with extracellular matrix. AcChoE bound to lipidic membranes is detergent extractable (DE AcChoE), whereas the enzyme associated with extracellular matrix is high salt soluble (HSS AcChoE). The latter variant is accumulated insynaptic regions by an unknown mechanism. 2. We have suggested previously that depolarization-induced Ca2+ influx is a major factor that modulates AcChoE synthesisin vivo, as well as the conversion of some DE AChoE to HSS variant. In the present study, we have examined (i) the effects of depolarization-induced skeletal muscle inactivity and ionophore-induced Ca2+ influxes on the expression of AcChoE molecular forms and (ii) the hypothesis that Ca2+-dependent calmodulin may be involved in the conversion of at least some forms of DE AcChoE to HSS variantin vivo. 3. Chick embryos were treatedin ovo during the early period of nervemuscle interactions withd-tubocurarine (dTC; a competitive neuromuscular blocking agent) or with decamethonium (dMET; a depolarizing agent). Both dTC and dMET equally and significantly reduced embryonic neuromuscular activity (motility). However, dTC significantly decreased AcChoE overall activity, whereas dMET had virtually no effect on AcChoE expression, compared to controls. 4. Treatment of embryos with the Ca2+ ionophore A23187 significantly increased the total AcChoE activity as well as the DE/HSS ratio of each AcChoE molecular form. However, treatment with N-(6-Aminohexyl)-5-chloro-1-naphthalenesulfonamide (also termed W-7), a calmodulin antagonist, did not alter the total AcChoE activity, but significantly increased the DE/HSS ratio of AcChoE forms. 5. These results support the idea that (i) depolarization and/or Ca2+ influxes, but not muscle contraction, may regulate AcChoE expression in skeletal muscle and (ii) Ca2+-dependent calmodulin activation may be involved in the conversion of some DE AcChoE to their HSS variantin vivo.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00733751
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