Electrophysiology of cultured human lens epithelial cells

The lens epithelial K+ conductance plays a key role in maintaining the lens ionic steady state. The specific channels responsible for this conductance are unknown. We used cultured lens epithelia and patch-clamp technology to address this problem. Human lens epithelial explants were cultured and after 1-4 passages were dissociated and used in this study. The cells from which we measured had a mean diameter of 31 +/- 1 microns (SEM, n = 26). The resting voltage was -19 +/- 4 mV (SEM, n = 10) and the input resistance was 2.5 +/- 0.5 G omega (SEM, n = 17) at -60 mV. Two currents were prominent in whole-cell recordings. An outwardly rectifying current was seen in nearly every cell. The magnitude of this current was a function of K+ concentration and was blocked by 3 mM tetraethylammonium. The instantaneous current-voltage relationship was linear in symmetric K+, implying that the outward rectification was due to gating. The current showed complex activation and inactivation kinetics. The second current seen was a transient inward current. This current had kinetics very similar to the traditional Na+ current of excitable cells and was blocked by 0.1 microM tetrodotoxin. In single-channel recordings, a 150-pS K+ channel and a 35-pS nonselective cation channel were seen but neither account for the macroscopic currents measured.