Marcus D C, Takeuchi S, Wangemann P
Biophysics Laboratory, Boys Town National Research Hospital, Omaha, Nebraska 68131.
Am J Physiol. 1992 Jun;262(6 Pt 1):C1423-9. doi: 10.1152/ajpcell.1992.262.6.C1423.
Patch-clamp recordings were made on cell-attached and excised apical membrane from dark cells of the semicircular canal of the gerbil. These cells are thought to secrete K+ and absorb Na+ from the luminal fluid (endolymph). Single-channel events were identified as being equally conductive (27.6 +/- 0.4 pS; n = 48) for K+, Na+, Rb+, Li+, and Cs+ and 1.4 times more permeable to NH4+ but not permeable to Cl-, Ca2+, Ba2+, nor to N-methyl-D-glucamine. The channels displayed linear current-voltage relations that passed nearly through the origin (intercept: -2.6 +/- 0.5 mV; n = 48) when conductive monovalent cations were present on both sides of the membrane in equal concentrations. Channel activity required the presence of Ca2+ at the cytosolic face; there was no activity at less than or equal to 10(-7) M Ca2+ and full activity at greater than or equal to 10(-5) M Ca2+. Cell-attached recordings had a mean reversal voltage of -36.4 +/- 7.9 mV (n = 7), which was interpreted to reflect the intracellular potential of dark cells under the present conditions. We have identified a nonselective cation channel in the apical membrane of vestibular dark cells that might participate in K+ secretion or Na+ absorption under stimulated conditions, but the density appears to be insufficient to fully account for the transepithelial K+ flux.
对沙鼠半规管暗细胞的细胞贴附式和分离的顶端膜进行了膜片钳记录。这些细胞被认为从管腔液（内淋巴）中分泌K⁺并吸收Na⁺。单通道事件被确定为对K⁺、Na⁺、Rb⁺、Li⁺和Cs⁺具有相同的电导（27.6±0.4 pS；n = 48），对NH₄⁺的通透性是前者的1.4倍，但对Cl⁻、Ca²⁺、Ba²⁺和N - 甲基 - D - 葡糖胺不通透。当膜两侧存在等浓度的导电单价阳离子时，这些通道呈现出几乎通过原点的线性电流 - 电压关系（截距：-2.6±0.5 mV；n = 48）。通道活性需要胞质面存在Ca²⁺；在Ca²⁺浓度小于或等于10⁻⁷ M时无活性，在大于或等于10⁻⁵ M时具有完全活性。细胞贴附式记录的平均反转电位为-36.4±7.9 mV（n = 7），这被解释为反映在当前条件下暗细胞的细胞内电位。我们在前庭暗细胞的顶端膜中鉴定出一种非选择性阳离子通道，其可能在刺激条件下参与K⁺分泌或Na⁺吸收，但密度似乎不足以完全解释跨上皮K⁺通量。
