乙酰胆碱对蟾蜍背根神经节神经元膜电位的影响及离子机制

EFFECT OF ACETYLCHOLINE ON MEMBRANE POTENTIAL IN TOAD DORSAL ROOT GANGLION NEURONS AND ITS IONIC BASIS

在离体灌流的蟾蜍背根神经节(DRG)标本上,用微电极进行胞内记录。在73个神经元中,依神经纤维的传导速度将神经元分为 A 型及 C 型,其中 A 型细胞67个,C 型6个,静息膜电位为-67.5±1.3mV((?)±SE)。当加4×10^(-4)—6×10^(-4)mol/L 乙酰胆碱(ACh),可观察到如下四种膜电位变化:1.超极化:幅值9.1±3.0mV((?)±SE,n=23);(2)去极化:幅值12.9±2.2mV((?)+SE,n=20);(3)双相反应(n=24):先超极化,后去极化,超极化幅值8.0±2.4mV((?)+SE),去极化幅值10.9±3.1mV((?)±SE);(4)无反应(n=6)。用阿托品(1.3×10^(-5)mol/L,n=23),或同时应用筒箭毒与六甲双铵(浓度均为1.4×10^(-5)mol/L,n=8)灌流,能分别阻断 ACh 引起的膜的超极化或去极化。ACh 引起超极化反应时膜电导平均增加13.8%,翻转电位值大约-96mV。四乙铵(TEA,20mmol/L)能使 ACh 的去极化幅值增加48.2±3.2%((?)±SE,n=6),超极化幅值减小79.4±4.3%((?)±SE,n=8)。MnCl_2(4mmol/L)使 ACh 的去极化及超极化幅值分别减小54.2±7.2%((?)±SE,n=5)及69.2±6.4%((?)±SE,n=14)。以上结果提示:ACh 引起的 DRG 神经细胞膜去极化反应由 N 型乙酰胆碱受体介导,而超极化反应由 Μ 型乙酰胆碱受体介导,前者可能包含了多种离子电导的改变,后者则可能与钾电导增加有关。

Intracellular recordings were made to investigate the effect of acetylcholine(ACh)on membrane potential of neurons in isolated toad dorsal root ganglion(DRG).In the 73 neurons examined,67 were of type A,and the remaining 6 oftype C cell.The resting membrane potential of these two types of cells was—67.5±1.3 mV((?)±SE).During the application of ACh(4×10^(-4)—6×10^(-4) mol/L)four types of the membrane potential changes were observed:(1)hyperpolariza-tion of 9.1±3.0 mV((?)±SE,n=23);(2)depolarization of 12.9±2.2 mV((?)±SE,n=20);(3)biphasic response,i.e.,hyperpolarization of 8.0±2.4 mV((?)±SE)followed by depolarization of 10.9±3.1 mV((?)±SE,n=24);(4)no change(n=6).The hyperpolarization induced by ACh could be blocked by atropine(1.3×10^(-5) mol/L,n=23),and ACh-induced depolarization could be abolished by co-perfusion of d-tubocurarine(1.4×10^(-5) mol/L)and hexamethonium(1.4×10^(-5)mol/L,n=18).During ACh hyperpolarization the membrane conductance wasincreased by 13.8% and the reversal potential was about-96 mV(n=3).TEA(20mmol/L)enhanced ACh depolarization amplitude by 48.2±3.2%((?)±SE,n=6),and depressed ACh hyperpolarization by 79.4±4.3%((?)±SE,n=8),MnCl_2(4 mmol/L)decreased the ACh depolarization and hyperpolarization by 54.2±7.2%(?)±SE,n=5)and by 69.2±6.4%((?)+SE,n=14)respectively.These results suggest that the depolarization and hyperpolarization inducedby ACh are mediated by nicotinic and muscarinic receptors on the neurons,respec-tively.ACh depolarization might involve changes in several kinds of ionic conduct-ances,and ACh hyperpolarization might be ascribed to increase of K conductance.