Fresh and cultured human lens epithelial cells: an electrophysiological study of cell coupling and membrane properties

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.