Jacob T J
Department of Pharmacology, St George's Hospital Medical School, London, U.K.
Exp Eye Res. 1988 Sep;47(3):489-506. doi: 10.1016/0014-4835(88)90059-0.
Microelectrode studies of fresh human and rabbit lens epithelia revealed stable membrane potentials [VR (human) = -36 mV; VR (rabbit) = -45 mV] and low input resistances [Ri (human) = 10 M omega; Ri (rabbit) = 20 M omega]. Coupling studies, using two voltage microelectrodes, demonstrated that the low input resistance of the fresh epithelial tissue was due to electrotonic coupling, which was found to be extremely labile and sensitive to perfusion of the apical (fibrefacing) surface of the epithelium. The intercellular coupling could be stabilized by raising the calcium concentration of the perfusate. Studies performed on confluent monolayers of cultured human lens epithelial (HLE) cells demonstrated a membrane potential (VR = -33 mV) and input resistance (Ri = 29 M omega) similar to their fresh counterparts. The intercellular coupling of these cells was found to be much more robust. Ultrastructural studies revealed that the apical junction of cultured HLE cells was less complex than that found in fresh tissue, the latter exhibiting multiple interdigitations and folds. The cultured monolayer was dissociated into single cells by a variety of methods and the membrane properties of individual cells were studied. Single cells were found to have a lower membrane potential (-20 to -25 mV) and an input resistance in the range 110-170 M omega, depending on the method of dissociation. Channel blocking and ion replacement studies revealed significant conductance pathways for potassium, sodium and chloride and a cell-attached patch clamp investigation revealed three distinct channel types. Of the two channels with inward currents at the resting potential, one, with a conductance of 25 pS, is identified as a non-selective cation channel, and the other, with a conductance of 14 pS and reversal potential of - 14 mV, is a possible candidate for a chloride channel but has yet to be characterized. A third channel with an outward current at the resting potential is identified as a potassium channel with a conductance of 49 pS. A link between epithelial uncoupling and certain types of cataract is proposed.
对新鲜的人及兔晶状体上皮进行的微电极研究显示，其膜电位稳定[人：VR = -36 mV；兔：VR = -45 mV]，输入电阻较低[人：Ri = 10 MΩ；兔：Ri = 20 MΩ]。使用两个电压微电极进行的耦合研究表明，新鲜上皮组织的低输入电阻是由电紧张耦合所致，且发现这种耦合极其不稳定，对上皮顶端（面向纤维）表面的灌注极为敏感。通过提高灌注液中的钙浓度可使细胞间耦合稳定。对培养的人晶状体上皮（HLE）细胞汇合单层进行的研究显示，其膜电位（VR = -33 mV）和输入电阻（Ri = 29 MΩ）与其新鲜对应物相似。发现这些细胞的细胞间耦合更为稳固。超微结构研究显示，培养的HLE细胞顶端连接比新鲜组织中的简单，新鲜组织呈现多个指状交叉和褶皱。通过多种方法将培养的单层解离为单个细胞，并研究单个细胞的膜特性。发现单个细胞具有较低的膜电位（-20至-25 mV），输入电阻在110 - 170 MΩ范围内，具体取决于解离方法。通道阻断和离子置换研究揭示了钾、钠和氯的重要电导途径，细胞贴附式膜片钳研究揭示了三种不同的通道类型。在静息电位下具有内向电流的两个通道中，一个电导为25 pS，被鉴定为非选择性阳离子通道，另一个电导为14 pS，反转电位为-14 mV，可能是氯离子通道的候选者，但尚未得到表征。在静息电位下具有外向电流的第三个通道被鉴定为电导为49 pS的钾通道。提出了上皮解偶联与某些类型白内障之间的联系。
