Ionic currents expressed in a cell line derived from the organ of Corti ofthe 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 t ransgenic mouse. permits cells to grow proliferatively at 33 degrees C and to differentiate at 39 degrees C. Whole-cell patch-clamp recordings showed that proliferating cells had a different electrophysiology to differentiati ng cells. Differentiating cells had a conditionally expressed slowly activa ting inward current activated by hyperpolarization. The current was not blo cked by extracellular application of 0.5 mM Ba2+, but was bloch-ed reversib ly 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 mu M forskolin. These properties iden tify the slowly activating current as I-h. A proportion of proliferating an d differentiating cells exhibited a voltage-gated Na+ current, I-Na. I-Na w as abolished in Na-free external medium and was inhibited reversibly by tet rodotoxin (TTX) with K-i=64 nM. Together these results suggest that prolife rating and differentiating hair cell precursors in the immortal cochlear ce ll line UB/OC-2 express currents which are also found in developing hair ce lls.