From the Department of Physiology, Harbin Medical University, China (D.-D.Z., Y.X., H.Z., X.-W.G., X.-X.M., L.G., J.-L.W., X.-P.D., R.G.).
Department of Pharmacology, New York Medical College, Valhalla (Z.-X.G., P.W., D.-H.L., W.-H.W.).
Hypertension. 2018 Aug;72(2):361-369. doi: 10.1161/HYPERTENSIONAHA.118.11070. Epub 2018 Jun 18.
Stimulation of BK2R (bradykinin [BK] B2 receptor) has been shown to increase renal Na excretion. The aim of the present study is to explore the role of BK2R in regulating Kir4.1 and NCC (NaCl cotransporter) in the distal convoluted tubule (DCT). Immunohistochemical studies demonstrated that BK2R was highly expressed in both apical and lateral membrane of Kir4.1-positive tubules, such as DCT. Patch-clamp experiments demonstrated that BK inhibited the basolateral 40-pS K channel (a Kir4.1/5.1 heterotetramer) in the DCT, and this effect was blocked by BK2R antagonist but not by BK1R (BK B1 receptor) antagonist. Whole-cell recordings also demonstrated that BK decreased the basolateral K conductance of the DCT and depolarized the membrane. Renal clearance experiments showed that BK increased urinary Na and K excretion. However, the BK-induced natriuretic effect was completely abolished in KS-Kir4.1 KO (kidney-specific conditional Kir4.1 knockout) mice, suggesting that Kir4.1 activity is required for BK-induced natriuresis. The continuous infusion of BK with osmotic pump for 3 days decreased the basolateral K conductance and the negativity of the DCT membrane. Western blot showed that infusion of BK decreased the expression of total NCC and phosphorylated NCC. Renal clearance experiments demonstrated that thiazide-induced natriuresis was blunted in the mice receiving BK infusion, suggesting that BK inhibited NCC function. Consequently, mice receiving BK infusion for 3 days were hypokalemic. We conclude that stimulation of BK2R inhibits NCC activity, increases urinary K excretion, and causes mice hypokalemia and that Kir4.1 is required for BK2R-mediated stimulation of urinary Na and K excretion.
BK2R（缓激肽 [BK] B2 受体）的刺激已被证明可增加肾脏的 Na 排泄。本研究旨在探讨 BK2R 在调节远端肾小管（DCT）中的 Kir4.1 和 NCC（NaCl 共转运体）中的作用。免疫组织化学研究表明，BK2R 在 Kir4.1 阳性管，如 DCT 的顶端和侧膜中高度表达。膜片钳实验表明，BK 抑制 DCT 中的基底外侧 40-pS K 通道（Kir4.1/5.1 异四聚体），该作用被 BK2R 拮抗剂阻断，但不受 BK1R（BK B1 受体）拮抗剂阻断。全细胞记录也表明，BK 降低了 DCT 的基底外侧 K 电导并使膜去极化。肾清除实验表明，BK 增加尿钠和钾排泄。然而，在 KS-Kir4.1 KO（肾脏特异性条件性 Kir4.1 敲除）小鼠中，BK 诱导的利尿作用完全被阻断，表明 Kir4.1 活性是 BK 诱导利尿所必需的。通过渗透泵连续输注 BK 3 天降低了 DCT 的基底外侧 K 电导和膜的负性。Western blot 显示，BK 输注降低了总 NCC 和磷酸化 NCC 的表达。肾清除实验表明，在接受 BK 输注的小鼠中，噻嗪类诱导的利尿作用减弱，表明 BK 抑制了 NCC 的功能。因此，接受 BK 输注 3 天的小鼠出现低钾血症。我们的结论是，BK2R 的刺激抑制了 NCC 的活性，增加了尿钾排泄，并导致小鼠低钾血症，而 Kir4.1 是 BK2R 介导的尿钠和钾排泄刺激所必需的。
