Ionic currents expressed in a cell line derived from the organ of Corti of the Immortomouse

 We have investigated the maturation of adult hair cell electrophysiology in a population of precursor cells in a conditionally immortal cell line. The cell line, UB/OC-2, from the embryonic organ of Corti of the H-2Kb-tsA58 transgenic mouse, permits cells to grow proliferatively at 33°C and to differentiate at 39°C. Whole-cell patch-clamp recordings showed that proliferating cells had a different electrophysiology to differentiating cells. Differentiating cells had a conditionally expressed slowly activating inward current activated by hyperpolarization. The current was not blocked by extracellular application of 0.5 mM Ba²⁺, but was blocked reversibly by 2 mM Cs⁺. The current was found to be carried by both K⁺ and Na⁺ ions (P _K/P _Na=2.2) and activated by 10 μM forskolin. These properties identify the slowly activating current as I _h. A proportion of proliferating and differentiating cells exhibited a voltage-gated Na⁺ current, I _Na. I _Na was abolished in Na-free external medium and was inhibited reversibly by tetrodotoxin (TTX) with K _i=64 nM. Together these results suggest that proliferating and differentiating hair cell precursors in the immortal cochlear cell line UB/OC-2 express currents which are also found in developing hair cells. Received: 6 January 1999 / Received after revision: 1 February 1999 / Accepted: 2 February 1999