Functional expression of TREK-2 K + channel in cultured rat brain astrocytes

Abstract

Background K + channels whose subunit contains four transmembrane segments and two pore-forming domains (4TM/2P) have been cloned recently. We studied whether 4TM/2P K + channels are functionally expressed in astrocytes that are known to have a large background (resting) K + conductance and a large resting membrane potential. Reverse transcriptase-PCR analysis showed that, among five 4TM/2P K + channels examined, TASK-1, TASK-3 and TREK-2 mRNAs were expressed in cultured astrocytes from rat cortex. In cell-attached patches, we mainly observed three K + channels with single-channel conductances of 30, 117 and 176 pS (−40 mV) in symmetrical 140 mM KCl. The 30 pS channel was the inward rectifying K + channel that has been previously described in astrocytes. The 117 pS K + channel also showed inward rectification and was insensitive to 1 mM tetraethylammonium and 1 mM 4-aminopyridine. The 176 pS channel was the Ca 2+-activated K + channel. The 117 pS K + channel was determined to be TREK-2, as judged by its electrophysiological properties and activation by membrane stretch, free fatty acids and intracellular acidosis. In ∼50% of astrocytes in culture, whole-cell K + current increased markedly following application of arachidonic acid. The number of TREK-2 channels in these cells was estimated to be ∼500–1000/cell. Our results show that TREK-2 is functionally expressed in cortical astrocytes in culture, and suggest that TREK-2 may be involved in K + homeostasis of astrocytes during pathological states.