Functional characterisation of human TASK-3, an acid-sensitive two-pore domain potassium channel.

Human TASK-3 (hTASK-3) is a recently identified member of the two-pore domain potassium channel (2PDKC) family which in man is predominantly expressed in the cerebellum. Previous preliminary examination of this channel indicates that when expressed in Xenopus oocytes, it produces a K(+) selective background conductance and consequent shift in resting membrane potential, thus mimicking other 2PDKC. Here we describe some additional functional and pharmacological aspects of hTASK-3-mediated conductances expressed in both Xenopus oocytes and HEK293 cells. hTASK-3 expression produces steady-state currents that approximate Goldman--Hodgkin--Katz behaviour with respect to membrane potential. Despite this, voltage steps from -80 mV to potentials > approximately -20 mV induce currents that exhibit a clear time-dependent increase in current amplitude. Kinetically, this increase in current was well fit by a single exponential, the time constant of which was approximately 10 ms and appeared independent of test potential, between -20 and +80 mV. In HEK293 cells hTASK-3 currents were inhibited by extracellular acidosis with a mid-point for inhibition of pH 6.4. Furthermore, the activity of TASK-3 was potentiated by the volatile anaesthetic halothane but inhibited by the local anaesthetic bupivacaine.