Differentiation-dependent changes in the membrane properties of fiber cells isolated from the rat lens.

Impedance measurements in whole lenses showed that lens fiber cells possess different permeability properties to the epithelial cells from which they differentiate. To confirm these observations at the cellular level, we analyzed the membrane properties of fiber cells isolated in the presence of the nonselective cation channel inhibitor Gd3+. Isolated fiber cells were viable in physiological [Ca2+] and exhibited a range of lengths that reflected their stage of differentiation. Analysis of a large population of fiber cells revealed a subgroup of cells whose conductivity matched values measured in the whole lens (1). In this group of cells, membrane resistance, conductivity, and reversal potential all varied with cell length, suggesting that the process of differentiation is associated with a change in the membrane properties of fiber cells. Using pharmacology and ion substitution experiments, we showed that newly differentiated fiber cells (<150 microm) contained variable combinations of Ba2+-and tetraethylammonium-sensitive K+ currents. Longer fiber cells (150-650 microm) were dominated by a lyotropic anion conductance, which also appears to plays a role in the intact lens. Longer cells also exhibited a low-level, nonselective conductance that was eliminated by the replacement of extracellular Na+ with N-methyl-d-glucamine, indicating that the lens contains both Gd3+-sensitive and -insensitive nonselective cation conductances. Fiber cell differentiation is therefore associated with a shift in membrane permeability from a dominant K+ conductance(s) toward larger contributions from anion and nonselective cation conductances as fiber cells elongate.