CALCIUM INFLUXES AND CALMODULIN MODULATE THE EXPRESSION AND PHYSICOCHEMICAL PROPERTIES OF ACETYLCHOLINESTERASE MOLECULAR-FORMS DURING DEVELOPMENT IN-VIVO

1. Acetylcholinesterase (AcChoE; EC 3.1.1.7) exists in several molecul ar forms that may be anchored to cell membranes or associated with ext racellular matrix. AcChoE bound to lipidic membranes is detergent extr actable (DE AcChoE), whereas the enzyme associated with extracellular matrix is high salt soluble (HSS AcChoE). The latter variant is accumu lated in synaptic regions by an unknown mechanism. 2. We have suggeste d previously that depolarization-induced Ca2+ influx is a major factor that modulates AcChoE synthesis in 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 a nd ionophore-induced Ca2+ influxes on the expression of AcChoE molecul ar 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 variant in vivo. 3. Chick embryos were treated in ovo during the earl y period of nerve-muscle interactions with d-tubocurarine (dTC; a comp etitive neuromuscular blocking agent) or with decamethonium (dMET; a d epolarizing agent). Both dTC and dMET equally and significantly reduce d embryonic neuromuscular activity (motility). However, dTC significan tly decreased AcChoE overall activity, whereas dMET had virtually no e ffect on AcChoE expression, compared to controls. 4. Treatment of embr yos with the Ca2+ ionophore A23187 significantly increased the total A cChoE activity as well as the DE/HSS ratio of each AcChoE molecular fo rm. However, treatment with N-(6-Aminohexyl)-5-chloro-1-naphthalenesul fonamide (also termed W-7), a calmodulin antagonist, did not alter the total AcChoE activity, but significantly increased the DE/HSS ratio o f AcChoE forms. 5. These results support the idea that (i) depolarizat ion and/or Ca2+ influxes, but not muscle contraction, may regulate AcC hoE expression in skeletal muscle and (ii) Ca2+-dependent calmodulin a ctivation may be involved in the conversion of some DE AcChoE to their HSS variant in vivo.