Eveloff J L, Calamia J
Am J Physiol. 1986 Jan;250(1 Pt 2):F176-80. doi: 10.1152/ajprenal.1986.250.1.F176.
The effects of a hypertonic extracellular medium on furosemide-sensitive Na and K fluxes were studied in isolated cells from the rabbit medullary thick ascending limb of Henle's loop (mTALH). In the control incubation medium, the furosemide-sensitive 22Na uptake was 379.1 +/- 24.4 pmol . mg protein-1 . min-1 and the furosemide-sensitive 86Rb uptake was 30.5 +/- 16.9. The furosemide-sensitive 22Na flux was not stimulated by K gradients directed into the cells, and, conversely, the furosemide-sensitive 86Rb flux was not stimulated by Na gradients directed into the cells. These findings are consistent with a Na-Cl cotransport system. In the presence of 200 mM mannitol, the furosemide-sensitive 22Na and 86Rb fluxes were increased dramatically to 919.4 +/- 76.6 and 106.1 +/- 29.2 pmol . mg protein-1 . min-1, respectively. When the osmolarity of the incubation medium was increased, not only were the furosemide-sensitive fluxes increased but these fluxes became inter-dependent, i.e., removing Na or K prevented the increase in the furosemide-sensitive flux of the other cation. This finding is consistent with a Na-K-2Cl cotransport system in the mTALH cells. The data suggest that the Na-Cl and the Na-K-2Cl cotransport systems may be distinct functions of the same furosemide-sensitive cotransport system and that their expression may be regulated by changes in cell volume.
在来自兔髓袢升支粗段（mTALH）的分离细胞中，研究了高渗细胞外介质对呋塞米敏感的钠和钾通量的影响。在对照孵育培养基中，呋塞米敏感的22Na摄取量为379.1±24.4 pmol·mg蛋白-1·min-1，呋塞米敏感的86Rb摄取量为30.5±16.9。呋塞米敏感的22Na通量不受导入细胞的钾梯度刺激，相反，呋塞米敏感的86Rb通量也不受导入细胞的钠梯度刺激。这些发现与钠-氯共转运系统一致。在存在200 mM甘露醇的情况下，呋塞米敏感的22Na和86Rb通量分别急剧增加至919.4±76.6和106.1±29.2 pmol·mg蛋白-1·min-1。当孵育培养基的渗透压增加时，不仅呋塞米敏感的通量增加，而且这些通量变得相互依赖，即去除钠或钾会阻止另一种阳离子的呋塞米敏感通量增加。这一发现与mTALH细胞中的钠-钾-2氯共转运系统一致。数据表明，钠-氯和钠-钾-2氯共转运系统可能是同一呋塞米敏感共转运系统的不同功能，并且它们的表达可能受细胞体积变化的调节。
