Dept. of Integrative Biology and Pharmacology, Univ. of Texas Health Science Center, 6431 Fannin St., Houston, TX 77030.
Am J Physiol Renal Physiol. 2013 Nov 1;305(9):F1277-87. doi: 10.1152/ajprenal.00363.2013. Epub 2013 Aug 28.
It is recognized that dopamine promotes natriuresis by inhibiting multiple transporting systems in the proximal tubule. In contrast, less is known about the molecular targets of dopamine actions on water-electrolyte transport in the cortical collecting duct (CCD). Epithelial cells in the CCD are exposed to dopamine, which is synthesized locally or secreted from sympathetic nerve endings. Basolateral K(+) channels in the distal renal tubule are critical for K(+) recycling and controlling basolateral membrane potential to establish the driving force for Na(+) reabsorption. Here, we demonstrate that Kir4.1 and Kir5.1 are highly expressed in the mouse kidney cortex and are localized to the basolateral membrane of the CCD. Using patch-clamp electrophysiology in freshly isolated CCDs, we detected highly abundant 40-pS and scarce 20-pS single channel conductances, most likely representing Kir4.1/5.1 and Kir4.1 channels, respectively. Dopamine reversibly decreased the open probability of both channels, with a relatively greater action on the Kir4.1/5.1 heterodimer. This effect was mediated by D2-like but not D1-like dopamine receptors. PKC blockade abolished the inhibition of basolateral K(+) channels by dopamine. Importantly, dopamine significantly decreased the amplitude of Kir4.1/5.1 and Kir4.1 unitary currents. Consistently, dopamine induced an acute depolarization of basolateral membrane potential, as directly monitored using current-clamp mode in isolated CCDs. Therefore, we demonstrate that dopamine inhibits basolateral Kir4.1/5.1 and Kir4.1 channels in CCD cells via stimulation of D2-like receptors and subsequently PKC. This leads to depolarization of the basolateral membrane and a decreased driving force for Na(+) reabsorption in the distal renal tubule.
人们认识到，多巴胺通过抑制近端小管中的多种转运系统来促进钠排泄。相比之下，人们对多巴胺作用于皮质集合管（CCD）水电解质转运的分子靶点知之甚少。CCD 中的上皮细胞暴露于多巴胺，多巴胺可以在局部合成或从交感神经末梢分泌。远端肾小管的基底外侧 K(+) 通道对于 K(+) 再循环和控制基底外侧膜电位以建立 Na(+) 重吸收的驱动力至关重要。在这里，我们证明 Kir4.1 和 Kir5.1 在小鼠肾脏皮质中高度表达，并定位于 CCD 的基底外侧膜。我们使用新鲜分离的 CCD 中的膜片钳电生理学检测到高度丰富的 40-pS 和稀少的 20-pS 单通道电导，它们很可能分别代表 Kir4.1/5.1 和 Kir4.1 通道。多巴胺可逆地降低了两种通道的开放概率，对 Kir4.1/5.1 异二聚体的作用相对更大。这种作用是通过 D2 样但不是 D1 样多巴胺受体介导的。PKC 阻断剂消除了多巴胺对基底外侧 K(+) 通道的抑制作用。重要的是，多巴胺显著降低了 Kir4.1/5.1 和 Kir4.1 单元电流的幅度。一致地，多巴胺诱导基底外侧膜电位的急性去极化，如在分离的 CCD 中直接使用电流钳模式监测到的。因此，我们证明多巴胺通过刺激 D2 样受体和随后的 PKC 抑制 CCD 细胞中的基底外侧 Kir4.1/5.1 和 Kir4.1 通道。这导致基底外侧膜去极化和远端肾小管中 Na(+) 重吸收的驱动力降低。
