Electrophysiological properties of paraventricular magnocellular neurons in rat brain slices: Modulation of I-A by angiotensin II
Electrophysiological properties of paraventricular magnocellular neurons in rat brain slices: Modulation of I-A by angiotensin II
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DOI：
10.1016/0306-4522(95)00434-3
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发表时间：
1996-03-01
期刊：
影响因子：
3.3
通讯作者：
Ferguson, AV
中科院分区：
文献类型：
--
作者：
Li, Z;Ferguson, AV
全细胞膜片钳记录获得的大细胞神经元的下丘脑室旁核在成年Sprague-Dawley大鼠脑切片制备已被用来检查三个外向钾电导和离子机制，通过血管紧张素II发挥其神经递质的行动在这个地区。荧光黄填充显示，我们记录的神经元具有11-17 μ m宽和22-35 μ m长的大卵形细胞体，以及1-3个最小分支突起，这些解剖特征与先前描述的大细胞神经内分泌神经元的解剖特征一致。这些神经元的平均静息膜电位为-58.3 +/- 0.9（平均值+/- S.E.M.）。mV，尖峰幅度为92.8 +/- 1.4 mV，输入电阻为788.9 +/- 50.4 M Ohm。这些细胞中的大多数显示出不规则或连续的自发活动，平均频率为2.44 +/- 0.33 Hz。电压钳记录显示三种外向钾电流：（1）延迟外向电流（I-K），（2）钙依赖外向电流（I-K（Ca））和（3）瞬时外向电流（I-A）。这些电流根据其电压依赖性、失活、Ca 2+依赖性和药理学进行分类。当去极化电位超过-40 mV时，I-K被激活，其振幅随去极化电位的增加而增加。对于去极化至+50 mV，该电流的膜电导为27.3 +/- 3.8 nS。在含2 mM Ca ~（2+）的培养基中，去极化至-20mV以上，引起缓慢激活的I-K（Ca），表现出最小的失活。该电流在无Ca ~（2+）/Co ~（2+）介质中受到抑制，其膜电导也比I-K小（+50 mV时为19.4 +/-3.5 nS）。I-A表现出快速激活和失活，并且只有在去极化脉冲步骤之前由条件超极化诱发。激活阈值约为-65 mV，随着测试电压阶跃变得更正，I-A振幅以非线性方式增加。I-A电导的90%最大值为15.7 +/- 1.1 nS，并且在约-15 mV的膜电位下观察到。这些电流的反转电位与K+平衡电位一致。四乙基铵可逆地抑制I-K的峰电流和稳态电流，而4-氨基吡啶则抑制I-A。用2 mM Co ~（2+）代替2 mM Ca ~（2+）或在无Ca ~（2+）的培养基中加入Co ~（2+）均能降低I-A的幅度，表明存在Co ~（2+）敏感的I-A。10（-7）M血管紧张素浴给药对I-K无显著影响，但导致I-A显著降低（-31.0 +/-4.1%），而AT（1）受体拮抗剂氯沙坦预处理后未观察到这种效应。我们得出结论，在室旁核大细胞中，像其他CNS神经元一样，至少三组钾通道对由去极化引起的外向电流有贡献。我们的数据还表明，通过离子机制，血管紧张素可能作用于AT（1）受体，影响下丘脑神经内分泌细胞的兴奋性。
Whole-cell patch-clamp recordings obtained from magnocellular neurons of the hypothalamic paraventricular nucleus in brain slice preparations of adult Sprague-Dawley rats have been utilized to examine three outward potassium conductances and the ionic mechanisms through which angiotensin II exerts its neurotransmitter actions within this region. Lucifer Yellow fills showed that neurons from which we recorded had large ovoid cell bodies 11-17 mu m wide and 22-35 mu m long, as well as 1-3 minimally branched processes, anatomical features in accordance with those previously described for magnocellular neuroendocrine neurons. These neurons had an average resting membrane potential of -58.3 +/- 0.9 (mean +/- S.E.M.) mV, spike amplitude of 92.8 +/- 1.4 mV, and input resistance of 788.9 +/- 50.4 M Ohm. Most of these cells displayed irregular or continuous spontaneous activity with a mean frequency of 2.44 +/- 0.33 Hz. Voltage-clamp recordings revealed three outward potassium currents; (1) a delayed outward current (I-K), (2) a Ca2+-dependent outward current (I-K(Ca)) and (3) a transient outward current (I-A). These currents were classified according to their voltage dependence, inactivation, Ca2+ dependence and pharmacology. The I-K was activated by depolarization beyond -40 mV and its amplitude consistently increased with depolarizing steps. The membrane conductance underlying this current was 27.3 +/- 3.8 nS for depolarization to +50 mV. In medium containing 2 mM Ca2+, depolarization to above -20 mV evoked a slowly-activating I-K(Ca) which showed minimal inactivation. This current was suppressed in Ca2+-free/Co2+ medium and its membrane conductance was also smaller (19.4 +/- 3.5 nS at +50 mV) than that of I-K. The I-A demonstrated both fast activation and inactivation and was evoked only if depolarizing pulse steps were preceded by conditioning hyperpolarization. The activation threshold was approximately -65 mV and I-A amplitude increased in non-linear fashion as test voltage steps became more positive. The 90% maximum of I-A conductance was 15.7 +/- 1.1 nS, and was observed at membrane potentials around -15 mV. The reversal potentials of these currents were in accordance with the K+ equilibrium potential. Tetra-ethylammonium reversibly inhibited both the peak and steady-state currents of the I-K, while 4-aminopyridine suppressed the I-A. Replacement of 2 mM Ca2+ with 2 mM Co2+ in our bath solution or addition of Co2+ into Ca2+-free medium reduced the magnitude of I-A, revealing the existence of a Co2+-sensitive I-A. Bath administration of 10(-7) M angiotensin was without significant effect on I-K, but resulted in a statistically significant reduction in I-A (-31.0 +/- 4.1%) in 12 of 14 paraventricular nucleus cells tested, effects which were not observed following pretreatment with the AT(1) receptor antagonist losartan.We conclude that in paraventricular nucleus magnocellular cells, like other CNS neurons, at least three sets of potassium channels contribute to the outward current evoked by depolarization. Our data also demonstrate ionic mechanisms through which angiotensin may act at AT(1) receptors to influence the excitability of hypothalamic neuroendocrine cells.