Raychowdhury Malay K, McLaughlin Margaret, Ramos Arnolt J, Montalbetti Nicolás, Bouley Richard, Ausiello Dennis A, Cantiello Horacio F
Renal Unit, Massachusetts General Hospital East, Charlestown, Massachusetts 02129, USA.
J Biol Chem. 2005 Oct 14;280(41):34718-22. doi: 10.1074/jbc.M507793200. Epub 2005 Aug 3.
The primary cilium is a ubiquitous, non-motile microtubular organelle lacking the central pair of microtubules found in motile cilia. Primary cilia are surrounded by a membrane, which has a unique complement of membrane proteins, and may thus be functionally different from the plasma membrane. The function of the primary cilium remains largely unknown. However, primary cilia have important sensory transducer properties, including the response of renal epithelial cells to fluid flow or mechanical stimulation. Recently, renal cystic diseases have been associated with dysfunctional ciliary proteins. Although the sensory properties of renal epithelial primary cilia may be associated with functional channel activity in the organelle, information in this regard is still lacking. This may be related to the inherent difficulties in assessing electrical activity in this rather small and narrow organelle. In the present study, we provide the first direct electrophysiological evidence for the presence of single channel currents from isolated primary cilia of LLC-PK1 renal epithelial cells. Several channel phenotypes were observed, and addition of vasopressin increased cation channel activity, which suggests the regulation, by the cAMP pathway of ciliary conductance. Ion channel reconstitution of ciliary versus plasma membranes indicated a much higher channel density in cilia. At least three channel proteins, polycystin-2, TRPC1, and interestingly, the alpha-epithelial sodium channel, were immunodetected in this organelle. Ion channel activity in the primary cilium of renal cells may be an important component of its role as a sensory transducer.
初级纤毛是一种普遍存在的、不运动的微管细胞器，缺乏运动性纤毛中存在的中央微管对。初级纤毛被一层膜包围，该膜具有独特的膜蛋白组成，因此在功能上可能与质膜不同。初级纤毛的功能在很大程度上仍然未知。然而，初级纤毛具有重要的感觉转导特性，包括肾上皮细胞对流体流动或机械刺激的反应。最近，肾囊性疾病与纤毛蛋白功能障碍有关。尽管肾上皮初级纤毛的感觉特性可能与该细胞器中的功能性通道活性有关，但在这方面仍然缺乏相关信息。这可能与评估这个相当小且狭窄的细胞器中的电活动所固有的困难有关。在本研究中，我们提供了首个直接的电生理证据，证明从LLC-PK1肾上皮细胞分离的初级纤毛存在单通道电流。观察到了几种通道表型，并且添加血管加压素会增加阳离子通道活性，这表明通过环磷酸腺苷途径对纤毛电导进行调节。纤毛膜与质膜的离子通道重建表明纤毛中的通道密度要高得多。在这个细胞器中免疫检测到至少三种通道蛋白，多囊蛋白-2、瞬时受体电位通道蛋白1，有趣的是，还有α-上皮钠通道。肾细胞初级纤毛中的离子通道活性可能是其作为感觉转导器作用的重要组成部分。
