Functional properties of the Na^+-sensitive Na^+ channel in tanycytes

方法：取成年小鼠（C57 BL/6 J）脑片，正中隆起（ME）水平冠状面切片，厚度200μm。结果：1）1 mM哇巴因（一种Na^+泵阻断剂）可显著增加细胞内Na ^+浓度（[Na^+] i）。（2）1-10μM苯扎米尔（Na^+/Ca^<2+>交换阻断剂）、100μM阿米洛利（上皮Na^+通道抑制剂）和1 mM根皮苷（Na^+/乳糖共转运体阻断剂）均可降低[Na^+]_i。3)当[Na^+]_o由对照值140 mM增加到160- 200 mM时，在ME中观察到[Na^+]_i的持续升高，而在其它区域中仅观察到较小的反应。4)当Na^+被胆碱或甘露醇替代时，这些反应消失。5)当[Na ^+]_o从140 mM降至100 mM时，[Na ^+]_i的变化非常小。6)在第三脑室外侧壁（3V）与ME之间的过渡区，当[Na ^+] o升高时，该区域的[Na^+] i降低。结果表明：（1）3V和ME脑区[Na^+] i的基础水平主要由Na^+泵、Na^+/Ca^<2+>交换器、（B）一个Na^+水平传感器，存在于血脑屏障缺失的ME中，当[Na^+]_o从维持的[Na ^+]_i水平中脱离时起作用。

Methods : Brain slices, sectioned coronally at the level of the median eminence(ME) with 200μm thickness, were obtained from adult mice(C57BL/6J). Slices were loaded with the Na^+-sensitive fluorescent dye SBFI(sodium-binding benzofuran isophthalate), and intracellular Na^+ images were monitored using an image analyzer ARGUS-50(Hamamatsu Photonics, Japan).Resulfls : 1)In all areas studied, the intracellular Na^+ concentration([Na^+]_i) was greatly increased by 1mM ouabain(a Na^+ pump blocker). 2)[Na^+]_i was decreased either by 1-10μM benzamil(a blocker of Na^+/Ca^<2+> exchanger), 100μM amiloride(an inhibitor of epithelial Na^+ channels(ENaCs)) or 1mM phloridzin(a blocker of Na^+/ghicose co-transporter). 3)When [Na^+]_o was raised from a control value of 140mM to 160-200mM, a sustained elevation in [Na^+]_i was observed in ME but only small responses were observed in the other regions. 4)The responses were abolished when Na^+ was substituted with choline or mannitol. 5)Very small changes were seen in [Na^+]_i when [Na^+]_o was decreased from 140mM to 100mM. 6)The transitional area between the lateral wall of third ventricle (3V) and the ME responded inversely, i.e. this area showed a decrease in [Na^+]_i when [Na^+]_o was elevated.Conclusions : The data indicate that (a)the basal level of [Na^+]_i in the brain regions lining 3V and ME is maintained chiefly by Na^+ pumps, Na^+/Ca^<2+> exchangers, ENaCs and Na^+/glucose co-transporters, and (b)a Na^+-level sensor, present in ME where the blood-brain barrier is absent, works when [Na^+]_o Aviates from the maintained [Na^+]_i level.