title: Depletion of total acetylcholine by hemicholinium-3 in isolated rat diaphragm is less in the presence of dexamethasone.
abstract: Low concentrations of dexamethasone (Dex) stimulate the initial rate of radioactive choline (Ch) accumulation in the endplate-rich area (EPA) of indirectly stimulated hemidiaphragms, while higher concentrations (greater than 0.6 microM) inhibit. This biphasic concentration-effect curve is found even in the presence of 26 microM hemicholinium-3 (HC-3), an inhibitor of Ch accumulation. In incubations (3 min) where the total hemidiaphragm acetylcholine (ACh) content is not altered by 26 microM HC-3, the inhibition by HC-3 of both the Ch accumulation rate and the incorporation of radioactive Ch into ACh in the EPA of stimulated tissues is less in the presence of 0.2 microM Dex. In 120 min incubations with 15 microM HC-3 and without added Ch, the tissue ACh content is depleted in both stimulated and unstimulated hemidiaphragms. In both cases the depletion of ACh is significantly less in the presence of 0.2 microM Dex. In stimulated tissues a comparable depletion of ACh due to 15 microM HC-3 is also found with 1 and 10 microM Ch added to the medium. It is significantly less when 0.2 microM Dex and 1 microM Ch are added to the medium. In 120 min incubations with stimulated tissue, the amount of "bound' ACh is increased by addition of 30 microM Ch to the medium, decreased in the presence of 0.2 microM Dex, and greatly decreased in the presence of 15 microM HC-3. In the presence of Dex plus HC-3, the decrease in the amount of "bound' ACh due to either Dex or HC-3 alone, is abolished provided that 30 microM Ch is also present.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000109:Acetylcholine / Q000032:analysis*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002794:Choline / Q000378:metabolism; D003714:Denervation; D003907:Dexamethasone / Q000494:pharmacology*; D003964:Diaphragm / Q000032:analysis*; D005260:Female; D006426:Hemicholinium 3 / Q000037:antagonists & inhibitors*; D066298:In Vitro Techniques; D009045:Motor Endplate / Q000378:metabolism; D009469:Neuromuscular Junction / Q000187:drug effects*; D051381:Rats
chemical_list: D006426:Hemicholinium 3; D003907:Dexamethasone; D002794:Choline; D000109:Acetylcholine