Department of Physiology, Xuzhou Medical University, Xuzhou, Jiangsu, China.
Department of Pharmacology, New York Medical College, Valhalla, New York.
Am J Physiol Renal Physiol. 2017 Apr 1;312(4):F682-F688. doi: 10.1152/ajprenal.00420.2016. Epub 2016 Nov 9.
Mice transgenic for genomic segments harboring PHAII (pseudohypoaldosteronism type II) mutant Wnk4 (with-No-Lysine kinase 4) (TgWnk4) have hyperkalemia which is currently believed to be the result of high activity of Na-Cl cotransporter (NCC). This leads to decreasing Na delivery to the distal nephron segment including late distal convoluted tubule (DCT) and connecting tubule (CNT). Since epithelial Na channel (ENaC) and renal outer medullary K channel (ROMK or Kir4.1) are expressed in the late DCT and play an important role in mediating K secretion, the aim of the present study is to test whether ROMK and ENaC activity in the DCT/CNT are also compromised in the mice expressing PHAII mutant Wnk4. Western blot analysis shows that the expression of βENaC and γENaC subunits but not αENaC subunit was lower in TgWnk4 mice than that in wild-type (WT) and TgWnk4 mice. Patch-clamp experiments detected amiloride-sensitive Na currents and TPNQ-sensitive K currents in DCT2/CNT, suggesting the activity of ENaC and ROMK. However, both Na and ROMK currents in DCT2/CNT of TgWnk4 mice were significantly smaller than those in WT and TgWnk4 mice. In contrast, the basolateral K currents in the DCT were similar among three groups, despite higher NCC expression in TgWnk4 mice than those of WT and TgWnk4mice. An increase in dietary K intake significantly increased both ENaC and ROMK currents in the DCT2/CNT of all three groups. However, high-K (HK) intake-induced stimulation of Na and K currents was smaller in TgWnk4 mice than those in WT and TgWnk4 mice. We conclude that ENaC and ROMK channel activity in DCT2/CNT are inhibited in TgWnk4 mice and that Wnk4-induced inhibition of ENaC and ROMK may contribute to the suppression of K secretion in the DCT2/CNT in addition to increased NCC activity.
携带有 PHAII（假性醛固酮增多症 II 型）突变 Wnk4（无赖氨酸激酶 4）基因片段的小鼠（TgWnk4）发生高钾血症，目前认为这是由于 Na-Cl 共转运蛋白（NCC）活性升高所致。这导致 Na 向包括远曲小管末段（DCT）和连接小管（CNT）在内的远端肾单位输送减少。由于上皮钠通道（ENaC）和肾外髓质 K 通道（ROMK 或 Kir4.1）在 DCT 中表达，并在介导 K 分泌中发挥重要作用，因此本研究旨在测试表达 PHAII 突变 Wnk4 的小鼠 DCT/CNT 中的 ROMK 和 ENaC 活性是否也受到损害。Western blot 分析显示，与野生型（WT）和 TgWnk4 小鼠相比，TgWnk4 小鼠的βENaC 和γENaC 亚基表达降低，但 αENaC 亚基表达无差异。在 DCT2/CNT 中，我们通过膜片钳实验检测到阿米洛利敏感的 Na 电流和 TPNQ 敏感的 K 电流，这表明 ENaC 和 ROMK 的活性。然而，与 WT 和 TgWnk4 小鼠相比，TgWnk4 小鼠 DCT2/CNT 中的 Na 和 ROMK 电流明显较小。相反，三组 DCT 的基底外侧 K 电流相似，尽管 TgWnk4 小鼠的 NCC 表达高于 WT 和 TgWnk4 小鼠。增加膳食 K 摄入显著增加了三组 DCT2/CNT 中的 ENaC 和 ROMK 电流。然而，与 WT 和 TgWnk4 小鼠相比，高钾（HK）摄入诱导的 Na 和 K 电流刺激较小。综上所述，我们得出结论，TgWnk4 小鼠的 DCT2/CNT 中的 ENaC 和 ROMK 通道活性受到抑制，Wnk4 诱导的 ENaC 和 ROMK 抑制可能除了增加 NCC 活性外，还会抑制 DCT2/CNT 中的 K 分泌。
