Department of Pharmacology and Systems Physiology, University of Cincinnati, Cincinnati, Ohio.
Am J Physiol Renal Physiol. 2021 Jun 1;320(6):F1165-F1173. doi: 10.1152/ajprenal.00062.2021. Epub 2021 May 10.
In 15% of cases, autosomal dominant polycystic kidney disease arises from defects in polycystin-2 (PC2). PC2 is a member of the polycystin transient receptor potential subfamily of cation-conducting channels and is expressed in the endoplasmic reticulum and primary cilium of renal epithelial cells. PC2 opposes a procystogenic influence of the cilium, and it has been proposed that this beneficial effect is mediated in part by a flow of Ca through PC2 channels into the primary cilium. However, previous efforts to determine the permeability of PC2 channels to Ca have yielded widely varying results. Here, we report the mean macroscopic Ca influx through native PC2 channels in the primary cilia of mIMCD-3 cells, which are derived from the murine inner medullary collecting duct. Under conditions designed to isolate inward Ca currents, a small inward Ca current was detected in cilia with active PC2 channels but not in cilia lacking those channels. The current was activated by the addition of 10 µM internal Ca, which is known to activate ciliary PC2 channels. It was blocked by 10 µM isosakuranetin, which blocks the same channels. On average, the current amplitude was -1.8 pA at -190 mV; its conductance from -50 to -200 mV averaged 20 pS. Thus, native PC2 channels of renal primary cilia are able to conduct a small but detectable Ca influx under the conditions tested. The possible consequences of this influx are discussed. In autosomal dominant polycystic kidney disease, it is proposed that Ca entering the primary cilium through polycystin-2 (PC2) channels may limit the formation of cysts. Recent studies predict that any macroscopic Ca influx through these channels should be small. We report that the native PC2 channels in primary cilia of cultured renal epithelial cells can allow a small macroscopic calcium influx. This may allow a significant accumulation of Ca in the cilium in vivo.
在 15%的情况下，常染色体显性多囊肾病是由多囊蛋白-2（PC2）的缺陷引起的。PC2 是多囊蛋白瞬时受体电位亚家族阳离子通道的成员，在肾上皮细胞的内质网和初级纤毛中表达。PC2 反对纤毛的囊泡形成影响，有人提出，这种有益的影响部分是通过 Ca 通过 PC2 通道流入初级纤毛的流动来介导的。然而，以前确定 PC2 通道对 Ca 的通透性的努力产生了广泛不同的结果。在这里，我们报告了源自小鼠内髓集合管的 mIMCD-3 细胞初级纤毛中天然 PC2 通道的平均宏观 Ca 流入量。在设计用于分离内向 Ca 电流的条件下，在具有活性 PC2 通道的纤毛中检测到小的内向 Ca 电流，但在没有这些通道的纤毛中未检测到。该电流通过添加 10μM 内部 Ca 激活，已知该 Ca 激活纤毛 PC2 通道。它被 10μM 异sakuranetin 阻断，该阻断剂阻断相同的通道。平均而言，在-190 mV 时，电流幅度为-1.8 pA；其在-50 至-200 mV 时的电导平均值为 20 pS。因此，在测试的条件下，肾初级纤毛中的天然 PC2 通道能够传导可检测的小 Ca 流入。讨论了这种流入的可能后果。在常染色体显性多囊肾病中，据推测，通过多囊蛋白-2（PC2）通道进入初级纤毛的 Ca 可能会限制囊肿的形成。最近的研究预测，这些通道的任何宏观 Ca 流入都应该很小。我们报告称，培养的肾上皮细胞初级纤毛中的天然 PC2 通道可以允许少量宏观 Ca 流入。这可能会导致体内纤毛中 Ca 的大量积累。
