Effect of vitamin E on acetylcholine-induced current in molluscan neurons: role of cytoplasmic free calcium and arachidonic acid.
Role of cytoplasmic concentration of free Ca2+ ([Ca]in) and arachidonic acid in potentiating the effect of vitamin E (DL-alpha-tocopherol) on acetylcholine receptor activity in Helix pomatia neurons was studied using a two-microelectrode intracellular recording, voltage clamp and fluorescent calcium probe fura-2 technique. Elevation of [Ca]in by intracellular injection from a microelectrode or by depolarizing pulses and application of 0.1 microM-0.1 mM vitamin E enhanced the acetylcholine-induced chloride current both in LP11 and RBc4 neurons. Application of 10 microM arachidonic acid to the same neurons decreased this current. The use of fluorescent probe showed that vitamin E did not essentially change [Ca]in, but an increase of [Ca]in intensified both the enhancing effect of vitamin E and the depressing effect of arachidonic acid. The enhancing effect of calcium influx was considerably decreased after vitamin E application. The antioxidant action of vitamin E was probably not involved in the mechanism of its enhancing effect on acetylcholine-induced current, since synthetic antioxidant, ionol, depressed acetylcholine responses. A spectrum analysis has shown the interaction between vitamin E and arachidonic acid in solution. This interaction may be considered as the molecular mechanism responsible for the prevention by vitamin E of steady arachidonic acid production from membrane phospholipids and its down-regulatory effect on acetylcholine receptor activity. Our results support this suggestion, since an inhibitor of phospholipase A2, 4-bromophenacyl bromide, mimicked the enhancing effect of vitamin E.
Dyatlov
V A
VA
Laboratory of Neurobiology, A.A. Bogomoletz Institute of Physiology, Ukrainian Academy of Sciences, Kiev.
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D016718:Arachidonic Acid / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D004594:Electrophysiology; D005724:Ganglia / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006372:Helix, Snails; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects*; D013056:Spectrophotometry, Ultraviolet; D014810:Vitamin E / Q000494:pharmacology*
D002712:Chlorides; D007473:Ion Channels; D014810:Vitamin E; D016718:Arachidonic Acid; D000109:Acetylcholine; D002118:Calcium