Adams D J, Nutter T J
Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, FL 33101.
J Physiol Paris. 1992;86(1-3):67-76. doi: 10.1016/s0928-4257(05)80009-9.
Neuronal nicotinic acetylcholine (ACh)-activated currents in rat parasympathetic ganglion cells were examined using whole-cell and single-channel patch clamp recording techniques. The whole-cell current-voltage (I-V) relationship exhibited strong inward rectification and a reversal (zero current) potential of -3.9 mV in nearly symmetrical Na+ solutions (external 140 mM Na+/internal 160 mM Na+). Isosmotic replacement of extracellular Na+ with either Ca2+ or Mg2+ yielded the permeability (Px/PNa) sequence Mg2+ (1.1) > Na+ (1.0) > Ca2+ (0.65). Whole-cell ACh-induced current amplitude decreased as [Ca2+]0 was raised from 2.5 mM to 20 mM, and remained constant at higher [Ca2+]0. Unitary ACh-activated currents recorded in excised outside-out patches had conductances ranging from 15-35 pS with at least three distinct conductance levels (33 pS, 26 pS, 19 pS) observed in most patches. The neuronal nicotinic ACh receptor-channel had a slope conductance of 30 pS in Na+ external solution, which decreased to 20 pS in isotonic Ca2+ and was unchanged by isosmotic replacement of Na+ with Mg2+. ACh-activated single channel currents had an apparent mean open time (tau 0) of 1.15 +/- 0.16 ms and a mean burst length (tau b) of 6.83 +/- 1.76 ms at -60 mV in Na+ external solution. Ca(2+)-free external solutions, or raising [Ca2+]0 to 50-100 mM decreased both the tau 0 and tau b of the nAChR channel. Varying [Ca2+]0 produced a marked decrease in NP0, while substitution of Mg2+ for Na+ increased NP0. These data suggest that activation of the neuronal nAChR channel permits a substantial Ca2+ influx which may modulate Ca(2+)-dependent ion channels and second messenger pathways to affect neuronal excitability in parasympathetic ganglia.
利用全细胞膜片钳和单通道膜片钳记录技术，研究了大鼠副交感神经节细胞中神经元烟碱型乙酰胆碱（ACh）激活电流。在近乎对称的Na⁺溶液（细胞外140 mM Na⁺/细胞内160 mM Na⁺）中，全细胞电流-电压（I-V）关系呈现出强烈的内向整流，反转（零电流）电位为-3.9 mV。用Ca²⁺或Mg²⁺等渗替代细胞外Na⁺，得到的通透性（Px/PNa）顺序为Mg²⁺（1.1）＞Na⁺（1.0）＞Ca²⁺（0.65）。随着[Ca²⁺]₀从2.5 mM升高到20 mM，全细胞ACh诱导的电流幅度降低，在更高的[Ca²⁺]₀时保持恒定。在切除的外侧向外膜片中记录的单位ACh激活电流的电导范围为15 - 35 pS，在大多数膜片中观察到至少三个不同的电导水平（33 pS、26 pS、19 pS）。在细胞外Na⁺溶液中，神经元烟碱型ACh受体通道的斜率电导为30 pS，在等渗Ca²⁺中降至20 pS，用Mg²⁺等渗替代Na⁺时电导不变。在细胞外Na⁺溶液中，-60 mV时ACh激活的单通道电流的表观平均开放时间（tau 0）为1.15±0.16 ms，平均爆发长度（tau b）为6.83±1.76 ms。无Ca²⁺的细胞外溶液，或将[Ca²⁺]₀提高到50 - 100 mM，会降低nAChR通道的tau 0和tau b。改变[Ca²⁺]₀会使NP0显著降低，而用Mg²⁺替代Na⁺会增加NP0。这些数据表明，神经元nAChR通道的激活允许大量Ca²⁺内流，这可能调节Ca²⁺依赖性离子通道和第二信使途径，从而影响副交感神经节中的神经元兴奋性。
