Large Conductance K+ Currents Expressed in Human Corneal Epithelial Cells

Abstract

Abstract: : Purpose: In the corneal epithelium the large conductance K⁺ channel plays critical roles in regulating cell volume and the resting membrane potential. This K⁺ channel was first discovered as a fenamate-activated and diltiazem-inhibited K⁺ current in the rabbit corneal epithelium. Recently we reported that this K⁺ current in the bovine corneal epithelium was also activated by some fatty acids including arachidonic acid, indicating that the K⁺ current originates from a background K⁺ channel inhibited by Gd³⁺. In this study on the human corneal epithelial cells, pharmacological properties of K⁺ currents were investigated to identify the channel type. Methods: Human corneal epithelial cells (HCEC, Kurabo, Japan) were cultured and isolated at the end of passage 4 or 5. The cells were perfused by HEPES-buffered Ringer solutions. Whole-cell currents were recorded using the perforated patch configuration of the patch clamp technique. Results: The zero potential of HCEC averaged -12 mV (n=78). HCEC expressed a noisy, non-inactivating outward current. No voltage-gated K⁺ current was detected. External application of flufenamic acid (0.1 mM, n=18) augmented an outwardly rectifying, noisy current with a reversal potential near the equilibrium potential of K⁺ (-80 mV), indicating high selectivity for K⁺. Similar K⁺ current augmentation were induced by arachidonic acid (0.02 mM, n=10) and palmitoleic acid (0.1 mM, n=8). The enhanced K⁺ current was blocked almost completely by subsequent application of 0.1 mM diltiazem. Gd³⁺ (0.5 mM) enhanced transiently (< 2 min) the fenamate-induced current augmentation. Conclusions: The human corneal epithelium exhibited the large conductance K⁺ current. The transient current augmentation by Gd³⁺ indicates its dual modulation of the K⁺ channel.  

Keywords: cornea: epithelium • ion channels • electrophysiology: non-clinical