Veldsema-Currie R D, Van Wilgenburg H, Labruyère W T, Langemeijer M W
Brain Res. 1984 Mar 5;294(2):315-25. doi: 10.1016/0006-8993(84)91043-6.
Low concentrations of dexamethasone (up to 200 nM) increase the accumulation of choline (Ch) and its incorporation into acetylcholine (ACh) in the endplate rich area (EPA) of stimulated and unstimulated diaphragms in the presence of 10 microM Ch. Tissue ACh is not significantly altered, even after 140 min incubation. The specific radioactivity of the ACh in the EPA is thus increased by dexamethasone (Dex). The corticosteroid has no effects on acetylcholinesterase or choline acetyltransferase in diaphragm extracts. In the same medium, the amplitudes of the MEPPs, MEPCs and EPCs are also increased by Dex. Neither the quantal content of the EPCs nor the MEPP frequency, nor the half decay time of the MEPCs are altered. Therefore Dex (200 nM) increases both the resting and evoked output, and turnover of ACh in rat diaphragm. Beta-bungarotoxin (beta-BuTx) antagonizes the Dex-induced increase in Ch accumulation and its incorporation into ACh, and abolishes the increases in MEPC- and EPC-amplitudes, providing further argument for a presynaptic effect of Dex. In continuously-stimulated diaphragms, beta-BuTx causes an accumulation of ACh which is much greater than in unstimulated tissue. This accumulation of ACh is less in the presence of Dex, provided that Dex is added before beta-BuTx. The interaction of Dex and beta-BuTx is discussed in terms of their possible presynaptic sites of action.
在存在10微摩尔胆碱（Ch）的情况下，低浓度地塞米松（高达200纳摩尔）可增加受刺激和未受刺激膈肌终板富集区（EPA）中胆碱（Ch）的积累及其掺入乙酰胆碱（ACh）的量。即使孵育140分钟后，组织中的乙酰胆碱（ACh）也没有显著变化。因此，地塞米松（Dex）增加了EPA中ACh的比放射性。皮质类固醇对膈肌提取物中的乙酰胆碱酯酶或胆碱乙酰转移酶没有影响。在相同培养基中，微小终板电位（MEPPs）、微小终板电流（MEPCs）和终板电流（EPCs）的幅度也会因Dex而增加。EPCs的量子含量、MEPP频率以及MEPCs的半衰期均未改变。因此，Dex（200纳摩尔）增加了大鼠膈肌中ACh的静息和诱发释放量以及周转率。β-银环蛇毒素（β-BuTx）可拮抗Dex诱导的Ch积累增加及其掺入ACh的过程，并消除MEPC和EPC幅度的增加，这为Dex的突触前效应提供了进一步的证据。在持续刺激的膈肌中，β-BuTx会导致ACh的积累，其积累量远大于未受刺激的组织。如果在加入β-BuTx之前加入Dex，那么在Dex存在的情况下，ACh的这种积累会减少。根据它们可能的突触前作用位点，对Dex和β-BuTx的相互作用进行了讨论。
