Characterization of voltage-gated, whole-cell ionic currents from conjunctival epithelial cells

PURPOSE. These studies were performed to characterize the voltage- gated, whole-cell ionic currents in rabbit bulbar conjunctival epithelial and goblet cells. METHODS. New Zealand White rabbits were killed, and the bulbar conjunctiva was isolated. Conjunctival cells were dissociated for patch clamp analysis of whole-cell currents. The amphotericin, perforated-patch, whole- cell technique was used. RESULTS. Conjunctival epithelial cells had a mean capacitance of 6.72 pF (SE = 0.49; n = 25). The primary currents found were an inwardly rectifying K⁺ current, a saturating K⁺ current, and an outwardly rectifying nonselective cation current. A second nonselective cation current also appeared to be present. The inward current was observed in a KCl Ringer's bath and was almost nonexistent in a NaCl bath. The current was Ba²⁺- and Cs⁺-sensitive. The second K⁺ current became saturated at depolarized voltages and was Ba²⁺- and quinidine-sensitive. The first outward nonselective cation current was typically less than 100 pA in amplitude and activated at voltages positive to 0 mV. Tail current experiments showed that the current was cation selective. The current was blocked by Gd³⁺ but not by the Cl^- current blockers 4,4'- diisothiocyanostilbene-2,2'-disulfonic acid or 5-nitro-2-(3- phenylpropylamino)benzoic acid. The second nonselective cation current was larger and Gd³⁺-insensitive. The primary current observed in goblet cells was a large outward K⁺ current. CONCLUSIONS. The primary currents observed during whole-cell patch clamping of bulbar conjunctival epithelium are a Ba²⁺- and Cs⁺-sensitive, inwardly rectifying K⁺ current, a saturating K⁺ current, and two outwardly rectifying nonselective cation currents. Goblet cells contain a large outward K⁺ current.