Relation between bicarbonate concentration and voltage dependence of sodium currents in freshly isolated CA1 neurons of the rat
Relation between bicarbonate concentration and voltage dependence of sodium currents in freshly isolated CA1 neurons of the rat
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DOI：
10.1152/jn.01083.2002
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发表时间：
2003-05-01
影响因子：
2.5
通讯作者：
Witte, OW
中科院分区：
文献类型：
--
作者：
Bruehl, C;Witte, OW
最近已经表明，全细胞钙和钠电流由CO2/HCO 3-缓冲盐水调节。虽然碳酸氢根离子（而不是二氧化碳）已被证明可以调节钙电流，但钠电流却缺乏这一信息。此外，还不知道调节的强度是否取决于碳酸氢盐浓度，或者它是否是一种全有或全无的现象。为了回答这些问题，我们采用全细胞电压钳技术对新鲜分离的大鼠海马CA 1区神经元。当用HEPES缓冲盐水灌注细胞时，-130 mV至-20 mV的电压阶跃引起幅度为-5.1 +/- 0.5 nA（平均值+/- SE，n = 17）的钠电流。该电流的幅度在随后的灌流过程中增加，其中溶液含有增加量的碳酸氢盐和CO2（%CO2/mM HCO 3-：2.5/5.6; 5.0/18; 10/37），在10%CO2/37 MHCO 3-中的最大增量为-6.9 +/- 0.8 nA。振幅的增加与线性负移相关（斜率：-0.7 mV/mM HCO 3-）（Δ V（h，a）：-19.4 +/- 1.8 mV，在10% CO2中），但最大电导没有改变（g（max）：HEPES：203.1 +/- 21.0 nS和10% CO2/37 mM HCO 3-：207.3 +/- 21.3 nS）。此外，半最大失活电位（V-h，V-i）向负电位方向移动（斜率：-0.6 mV/mM HCO 3-），碳酸氢盐和CO2的量增加（HEPES：-53.6 +/- 11.8 mV; 10% CO2/37 mM HCO3-：-69.8 +/- 2.1 mV），使得电流幅度对静息膜电位下的小电位变化高度敏感。当细胞暴露于含有不同量碳酸氢盐（5.6; 18; 26 mM）但恒定CO2（5%）的溶液时，电压依赖性出现相同的负向偏移，V-h、V-a的斜率为-0.5 mV/mM HCO 3-，V-h、V-i的斜率为-0.5 mV/mM HCO 3-。同样，碳酸氢盐浓度和g（max）大小之间没有相关性。当电流诱发含有恒定浓度（18 mM）的碳酸氢盐，但不同量的CO2（2.5; 5.0 - 10%）的溶液中，没有观察到显着的变化。目前的数据表明，碳酸氢根离子，而不是二氧化碳，调制电压门控钠电流的浓度依赖性方式。由于钠电流的幅度对伴随碳酸氢根量增加的膜电位变化变得高度敏感，因此在该离子的浓度可以改变的情况下（如代谢性酸中毒、代谢性酸中毒和高碳酸血症），这可能对神经元网络的兴奋性至关重要。
It recently has been shown that whole cell calcium and sodium currents are modulated by CO2/HCO3--buffered saline. While the bicarbonate ion, but not CO2, has been proven to modulate calcium currents, this information is lacking for sodium currents. Furthermore, it is not known whether the strength of modulation dependents on the bicarbonate concentration or whether it is an all-or-nothing phenomenon. To answer these questions, we used the whole cell voltage-clamp technique on freshly isolated hippocampal CA1 neurons from the rat. A voltage step from -130 to -20 mV elicited a sodium current with an amplitude of -5.1 +/- 0.5 nA ( mean +/- SE, n = 17) when cells were superfused with HEPES-buffered saline. The amplitude of this current increased during a subsequent superfusion with solutions containing increasing amounts of bicarbonate and CO2 (%CO2/mM HCO3-: 2.5/5.6; 5.0/18; 10/37), with a maximal increment in 10% CO2/37 MHCO3- of -6.9 +/- 0.8 nA. The increase in amplitude was associated with a linear negative shift ( slope: -0.7 mV/mM HCO3-) of the potential of half-maximal activation (DeltaV(h,a): -19.4 +/- 1.8 mV in 10% CO2) but not with an alteration in the maximal conductance (g(max): HEPES: 203.1 +/- 21.0 nS and 10% CO2/37 mM HCO3-: 207.3 +/- 21.3 nS). In addition, the potential of half-maximal inactivation (V-h,V-i) shifted to more negative potentials ( slope: -0.6 mV/mM HCO3-) with increasing amounts of bicarbonate and CO2 ( HEPES: -53.6 +/- 11.8 mV; 10% CO2/37 mM HCO3-: -69.8 +/- 2.1 mV), making the amplitude of the current highly sensitive for small potential changes at resting membrane potential. The same negative shift in voltage dependence arose when cells were exposed to solutions with different amounts of bicarbonate (5.6; 18; 26 mM) but constant CO2 ( 5%) with slope rates of -0.5 mV/mM HCO3- for V-h,V-a and -0.5 mV/mM HCO3- for V-h,V-i. Again, there was no correlation between bicarbonate concentration and the size of g(max). When currents were evoked in solutions containing a constant concentration ( 18 mM) of bicarbonate but different amounts of CO2 (2.5; 5.0 10%), no significant changes have been observed. The present data demonstrate that bicarbonate ions, and not CO2, modulate voltage-gated sodium currents in a concentration-dependent manner. Because the amplitude of the sodium current becomes highly sensitive to membrane potential changes concomitant with increased bicarbonate amounts, this may be critical for the excitability of the neuronal network in situations ( like metabolic acidosis, respiratoric alkalosis and hypercapnia) in which the concentration of this ion can alter.