Potential identification of the O2-sensitive K+ current in a human neuroepithelial body-derived cell line

1 School of Biomedical Sciences and 2 Institute for Cardiovascular Research, University of Leeds, Leeds LS2 9JT, United Kingdom Whole cell recording of H-146 cells revealed that the outward K + current was completely inhibited by quinidine (IC 50 ~17 µM). In contrast, maximal concentrations of 4-aminopyridine (4-AP; 10 mM) reversibly blocked only ~60% (IC 50 ~1.52 mM). Ten millimolar 4-AP had no effect on the inhibition by hypoxia, which reduced current density from ~27 to ~13 pA/pF, whereas 1 mM quinidine abolished the hypoxic effect. In current clamp, 10 mM 4-AP depolarized the cell by ~18 mV and hypoxia caused further reversible depolarization of ~4 mV. One millimolar quinidine collapsed the membrane potential and abrogated any further hypoxic depolarization. RT-PCR revealed expression of the acid-sensitive, twin P domain K + channel TASK but not of TWIK, TREK, or the known hypoxia-sensitive Kv2.1, which was confirmed by sequencing and further PCR with primers to the coding region of TASK. However, a reduction in extracellular pH had no effect on K + current. Thus, although the current more closely resembles TWIK than TASK pharmacologically, structurally the reverse appears to be true. This suggests that a novel acid-insensitive channel related to TASK may be responsible for the hypoxia-sensitive K + current of these cells. potassium channels; chemoreceptor; hypoxia; TASK