Department of Pharmacology, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil.
J Mol Neurosci. 2010 Jan;40(1-2):138-42. doi: 10.1007/s12031-009-9228-1. Epub 2009 Aug 18.
New compounds that target nicotinic receptors (nAChRs) have been sought to correct disorders affecting cholinergic transmission in central and peripheral synapses. A quaternary derivate of l-hyoscyamine, phenthonium (Phen), was shown by our group to enhance the spontaneous acetylcholine (ACh) release without altering the nerve-induced transmitter release at the neuromuscular junction. The effect was unrelated to membrane depolarization, and was not induced by an increase of calcium influx into the nerve terminal. Phen also presented a competitive antimuscarinic activity and blocked noncompetitively the neuromuscular transmission. In this work we re-examined the mechanisms underlying the facilitatory actions of Phen on [(3)H]-ACh release in isolated ganglia of the guinea pig ileal myenteric plexus. Exposure of the preparations to Phen (10-50 microM) increased the release of [(3)H]-ACh by 81 to 68% over the basal. The effect was not affected by the ganglionic nAChR antagonist hexamethonium (1 nM) at a concentration that inhibited the increase of [(3)H]-ACh release induced by the nicotinic agonist dimethylphenylpiperazinium (DMPP, 30 microM). Association of Phen (10 microM) with DMPP potentiated the facilitatory effect of Phen. [(3)H]-ACh release was not altered by the muscarinic antagonists atropine (1 nM) or pirenzepine (1 microM). However, both antagonists inhibited the release of [(3)H]-ACh induced by either the muscarinic M1 agonist McN-343 (10 microM) or Phen (20 microM). The facilitatory effect of Phen was not altered by CdCl(2) (50 mM), but it was potentiated in the presence of tetraethylammonium (40 mM). The results indicate that the facilitatory action of Phen appears to be mediated by an increase of the inwardly rectifying potassium channels conductance probably related to the compound antimuscarinic activity.
我们的研究小组曾发现，莨菪烷的季铵衍生物苯甲托品（Phen）能增强乙酰胆碱（ACh）的自发性释放，而不改变神经肌肉接头处神经诱导的递质释放。这种作用与膜去极化无关，也不是由神经末梢钙离子内流增加引起的。苯甲托品还具有竞争性抗毒蕈碱活性，并能非竞争性地阻断神经肌肉传递。在这项工作中，我们重新研究了 Phen 促进豚鼠回肠肌间神经丛分离神经节中 [(3)H]-ACh 释放的作用机制。将制剂暴露于 Phen（10-50μM）中，可使 [(3)H]-ACh 的释放增加 81%至 68%，超过基础水平。该作用不受浓度为 1 nM 的烟碱型乙酰胆碱受体拮抗剂六烃季铵（hexamethonium）的影响，而该浓度可抑制烟碱激动剂二甲基苯基哌嗪（dimethylphenylpiperazinium，DMPP，30μM）引起的 [(3)H]-ACh 释放增加。Phen（10μM）与 DMPP 联合可增强 Phen 的促进作用。1 nM 的毒蕈碱拮抗剂阿托品（atropine）或 1μM 的哌仑西平（pirenzepine）均不改变 [(3)H]-ACh 的释放。然而，这两种拮抗剂均可抑制 M1 型毒蕈碱受体激动剂 McN-343（10μM）或 Phen（20μM）诱导的 [(3)H]-ACh 释放。50mM 的氯化镉（CdCl2）不改变 Phen 的促进作用，但在 40mM 的四乙铵（tetraethylammonium）存在下可增强其作用。结果表明，Phen 的促进作用可能是通过增加内向整流钾通道的电导来介导的，这可能与该化合物的抗毒蕈碱活性有关。
