Liu Xiao-Hong, Zhang Wenbo, Fisher Thomas E
Department of Physiology, College of Medicine, 107 Wiggins Road, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5.
J Physiol. 2005 Oct 1;568(Pt 1):61-8. doi: 10.1113/jphysiol.2005.093773. Epub 2005 Aug 11.
The magnocellular neurosecretory cells of the hypothalamus (MNCs) regulate water balance by releasing vasopressin and oxytocin as a function of plasma osmolality. Release is determined largely by the rate and pattern of action potentials generated in the MNC somata. Changes in firing are mediated in part by a stretch-inactivated non-selective cation current that causes the cells to depolarize when increased osmolality leads to cell shrinkage. We have obtained evidence for a new current that may regulate MNC firing during changes in external osmolality, using whole-cell patch clamp of acutely isolated rat MNC somata. In internal and external solutions lacking K+, with high concentrations of TEA, and with Na+ as the only likely permeant cation, the current appears as a slow inward current during depolarizations and yields a large tail current upon return to the holding potential of -80 mV. Approximately 60% of the MNCs tested (79 out of 134 cells) displayed a large increase in tail current density (from 5.2+/-0.9 to 10.5+/-1.4 pA pF-1; P<0.001) following an increase in external osmolality from 295 to 325 mosmol kg-1. The current is activated by depolarization to potentials above -60 mV and does not appear to depend on changes in internal Ca2+. The current is carried by Na+ under these conditions, but is blocked by Cs+ and Ba2+ and by internal K+, which suggests that the current could be a K+ current under physiological conditions. This current could play an important role in regulating the response of MNCs to osmolality.
下丘脑的大细胞神经分泌细胞（MNCs）通过根据血浆渗透压释放血管加压素和催产素来调节水平衡。释放主要由MNC胞体中产生的动作电位的速率和模式决定。放电的变化部分由一种牵张失活的非选择性阳离子电流介导，当渗透压升高导致细胞收缩时，该电流会使细胞去极化。我们使用急性分离的大鼠MNC胞体的全细胞膜片钳技术，获得了一种新电流的证据，该电流可能在外部渗透压变化期间调节MNC放电。在缺乏K +的内部和外部溶液中，加入高浓度的TEA，并且以Na +作为唯一可能的通透阳离子时，该电流在去极化期间表现为缓慢的内向电流，并且在回到-80 mV的保持电位时产生大的尾电流。在外部渗透压从295增加到325 mosmol kg-1后，大约60%测试的MNCs（134个细胞中的79个）显示尾电流密度大幅增加（从5.2±0.9增加到10.5±1.4 pA pF-1；P<0.001）。该电流通过去极化到高于-60 mV的电位而激活，并且似乎不依赖于内部Ca2+的变化。在这些条件下，该电流由Na +携带，但被Cs +、Ba2+和内部K +阻断，这表明该电流在生理条件下可能是一种K +电流。这种电流可能在调节MNCs对渗透压的反应中起重要作用。
