Takeuchi S, Ando M, Kozakura K, Saito H, Irimajiri A
Department of Physiology, Kochi Medical School, Nankoku, Japan.
Hear Res. 1995 Mar;83(1-2):89-100. doi: 10.1016/0378-5955(94)00191-r.
The basolateral membrane of isolated strial marginal cells has been probed for conductive pathways by the patch-clamp technique. Two types of voltage-insensitive channels were identified in both cell-attached and excised patches. Of these, frequently (69% of excised patches) observed was a Ca(2+)-activated nonselective cation channel having a unit conductance of 24.9 +/- 0.5 pS (N = 16). Other characteristics of this type in excised patches include: 1) linear I-V relations with 150 mM K+ (pipette)/150 mM Na+ (bath), 2) a permeability sequence of NH4+ > Na+ = K+ = Rb+ > Li+, 3) a flickering block by quinine or quinidine (both 1 mM), and 4) a dose dependent block of its activity by ADP or ATP (IC50,ATP/IC50,ADP = 20-35), both from the cytosolic side. Channels with similar characteristics were found in the apical membrane of the same cell; however, the basolateral channels were 2-4 times more densely distributed than the apical counterparts. Also frequently (57%) detected was a Cl- channel of 80.0 +/- 0.5 pS (N = 6), whose activity was Ca2+ independent. Additionally, this Cl- channel had: 1) linear I-V relations with symmetric Cl-, 2) a permeability sequence of Cl- > Br- > I- > or = NO3- > or = gluconate-, and 3) a complete and reversible block by 1 mM diphenylamine-2-carboxylate. In contrast to the apical Cl- channels, the basolateral ones had a much higher density (57% vs. < 1%) as well as a higher unit conductance (80 pS vs. 50 pS) than the apical counterpart. The relative abundance of these two types as the major conductive pathways for Na+, K+, and Cl- in the basolateral region must be taken into account when addressing the role of strial marginal cells in generating the positive endocochlear potential. The Cl- channel may facilitate Cl- distribution across the basolateral membrane.
运用膜片钳技术对分离的血管纹边缘细胞的基底外侧膜的传导通路进行了检测。在细胞贴附式膜片和游离膜片中均鉴定出两种电压不敏感通道。其中，经常观察到（69%的游离膜片）一种钙激活非选择性阳离子通道，其单位电导为24.9±0.5 pS（N = 16）。该类型通道在游离膜片中的其他特性包括：1）在150 mM K⁺（微电极内液）/150 mM Na⁺（浴液）条件下呈线性电流-电压关系；2）通透性顺序为NH₄⁺＞Na⁺ = K⁺ = Rb⁺＞Li⁺；3）可被奎宁或奎尼丁（均为1 mM）产生闪烁性阻断；4）从胞质侧，其活性可被ADP或ATP呈剂量依赖性阻断（IC₅₀，ATP/IC₅₀，ADP = 20 - 35）。在同一细胞的顶端膜中也发现了具有类似特性的通道；然而，基底外侧通道的分布密度是顶端对应通道的2 - 4倍。还经常检测到（57%）一种电导为80.0±0.5 pS的氯离子通道（N = 6），其活性不依赖于Ca²⁺。此外，该氯离子通道具有：1）在对称氯离子条件下呈线性电流-电压关系；2）通透性顺序为Cl⁻＞Br⁻＞I⁻≥NO₃⁻≥葡萄糖酸盐⁻；3）可被1 mM二苯胺-2-羧酸盐完全且可逆地阻断。与顶端氯离子通道相比，基底外侧的氯离子通道不仅密度更高（57%对＜1%），而且单位电导也更高（80 pS对50 pS）。在探讨血管纹边缘细胞在产生内淋巴正电位中的作用时，必须考虑这两种类型通道作为基底外侧区域Na⁺、K⁺和Cl⁻主要传导通路的相对丰度。氯离子通道可能有助于氯离子在基底外侧膜上的分布。
