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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 (IC50 ~17
µM). In contrast, maximal concentrations of
4-aminopyridine (4-AP; 
10 mM) reversibly blocked only ~60%
(IC50 ~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
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