Park Kyu-Sang, Cha Seung-Kyu, Kim Min-Jeong, Kim Dae-Ran, Jeong Seong-Woo, Lee Joong-Woo, Kong In Deok
Department of Physiology and Institute of Basic Medical Science, Yonsei University Wonju College of Medicine, Wonju, South Korea.
Pflugers Arch. 2006 Sep;452(6):775-83. doi: 10.1007/s00424-006-0086-1. Epub 2006 May 20.
We identified major subunits of the nicotinic acetylcholine receptor (nAChR) involved in excitatory postsynaptic potential and intracellular Ca(2+) ([Ca(2+)]i) increase in the major pelvic ganglion (MPG) neurons of the male rat. ACh elicited fast inward currents in both sympathetic and parasympathetic MPG neurons. Mecamylamine, a selective antagonist for alpha3beta4 nAChR, potently inhibited the ACh-induced currents in sympathetic and parasympathetic neurons (IC(50); 0.53 and 0.22 microM, respectively). Furthermore, alpha-conotoxin AuIB (10 microM), a new selective antagonist for alpha3beta4 nAChR, blocked more than 80% of the ACh-induced currents in MPG neurons. Conversely, alpha-bungarotoxin, alpha-methyllycaconitine, and dihydro-beta-erythroidine, known as blockers of the alpha7 or alpha4beta2, did not show selective blocking effects on MPG neurons. ACh transiently increased [Ca(2+)]i which was subsequently abolished in the extracellular Ca(2+)-free environment. Simultaneous recording of [Ca(2+)]i and ionic currents revealed that ACh increased [Ca(2+)]i under the conditions of the voltage-clamped (at -80 mV) state, and this resulted from the influx through nAChR itself. ACh-induced [Ca(2+)]i increase was blocked by mecamylamine (10 microM), but was not affected by atropine (1 microM). RT-PCR analysis showed that, among subunits of nAChR, alpha3 and beta4 were predominantly expressed in MPG. We suggest that activation of alpha3 and beta4 nAChR subunits in MPG neurons induce fast inward currents and [Ca(2+)]i increase, possibly mediating a major role in pelvic autonomic synaptic transmission.
我们确定了参与雄性大鼠主要盆神经节（MPG）神经元兴奋性突触后电位和细胞内Ca(2+)（[Ca(2+)]i）增加的烟碱型乙酰胆碱受体（nAChR）的主要亚基。乙酰胆碱（ACh）在交感和副交感MPG神经元中均引发快速内向电流。美加明是α3β4 nAChR的选择性拮抗剂，能有效抑制交感和副交感神经元中ACh诱导的电流（IC(50)分别为0.53和0.22微摩尔）。此外，α-芋螺毒素AuIB（10微摩尔）是α3β4 nAChR的新型选择性拮抗剂，可阻断MPG神经元中80%以上的ACh诱导电流。相反，已知为α7或α4β2阻滞剂的α-银环蛇毒素、α-甲基-lycaconitine和二氢-β-刺桐碱对MPG神经元未显示出选择性阻断作用。ACh短暂增加[Ca(2+)]i，随后在无细胞外Ca(2+)的环境中被消除。[Ca(2+)]i和离子电流的同步记录显示，在电压钳制（-80 mV）状态下，ACh增加[Ca(2+)]i，这是由于通过nAChR本身的内流所致。ACh诱导的[Ca(2+)]i增加被美加明（10微摩尔）阻断，但不受阿托品（1微摩尔）影响。逆转录-聚合酶链反应（RT-PCR）分析表明，在nAChR的亚基中，α3和β4在MPG中主要表达。我们认为，MPG神经元中α3和β4 nAChR亚基的激活诱导快速内向电流和[Ca(2+)]i增加，可能在盆腔自主神经突触传递中起主要作用。
