Extracellular acidification exerts opposite actions on TREK1 and TREK2 potassium channels via a single conserved histidine residue

Abstract

Mechanosensitive K ؉ channels TREK1 and TREK2 form a subclass of two P-domain K ؉ channels. They are potently activated by polyunsaturated fatty acids and are involved in neuroprotection, anesthesia, and pain perception. Here, we show that acidification of the extracellular medium strongly inhibits TREK1 with an apparent pK near to 7.4 corresponding to the physiological pH. The all-ornone effect of pH variation is steep and is observed within one pH unit. TREK2 is not inhibited but activated by acidification within the same range of pH, despite its close homology with TREK1. A single conserved residue, H126 in TREK1 and H151 in TREK2, is involved in proton sensing. This histidine is located in the M1P1 extracellular loop preceding the first P domain. The differential effect of acidification, that is, activation for TREK2 and inhibition for TREK1, involves other residues located in the P2M4 loop, linking the second P domain and the fourth membrane-spanning segment. Structural modeling of TREK1 and TREK2 and site-directed mutagenesis strongly suggest that attraction or repulsion between the protonated side chain of histidine and closely located negatively or positively charged residues in P2M4 control outer gating of these channels. The differential sensitivity of TREK1 and TREK2 to external pH variations discriminates between these two K ؉ channels that otherwise share the same regulations by physical and chemical stimuli, and by hormones and neurotransmitters.ion channel ͉ mutagenesis ͉ structural modeling T REK1 and TREK2 are two pore-domain K ϩ (K 2P ) channels sharing 78% of sequence homology (1-3). They are expressed in large amount in the nervous system (1, 3). In mouse brain, they display both overlapping and distinct distributions (4). TREK1 is highly expressed in the striatum and the cortex and TREK2 in the cerebellar granule cell layer. The two channels are detected in the hippocampus. Unlike other K 2P channels like the TASK channels, TREK1 and TREK2 are not very active at room temperature, but can be stimulated by a wide range of stimuli, including mechanical stretch (5), cell swelling (5), intracellular acidification (6, 7), heat (8, 9), lysophospholipids (10), and polyunsaturated fatty acids (PUFAs) such as arachidonic acid (AA) (5), and by pharmacological agents such as volatile anesthetics (1, 11) and riluzole (12), a drug used to protect motoneurons in amyotrophic lateral sclerosis. Both TREK1 and TREK2 are inhibited by neurotransmitters and hormones that activate protein kinase A and C pathways resulting in phosphorylation of conserved residues in their cytoplasmic C-ter (5, 13, 14). TREK1 and TREK2 also share interacting partners in the brain (15,16). A kinase anchoring protein (AKAP) 150 is one of them. By binding to a major regulatory site of the TREK channels, AKAP150 transforms low activity outwardly rectifying channels into robust leak channels that become largely insensitive to AA, stretch, and internal acidification. Inhibition by Gs-coupled receptors is conserved but inhibition by Gq-co...

Heterodimerization within the TREK channel subfamily produces a diverse family of highly regulated potassium channels

“…5 B and C). In contrast to TREK2, TRAAK is inhibited by external acidification, but more weakly than TREK1 (11). As expected, TREK1-TRAAK was inhibited by external acidification but the observed inhibition was intermediate in amplitude between what is seen in TREK1 (highly sensitive) and TRAAK (poorly sensitive) (Fig.…”

“…Intracellular acidification stimulates both TREK1 and TREK2 (8,9), whereas TRAAK is stimulated by intracellular alkalinization (10). In contrast, extracellular acidification is able to inhibit TREK1 and TRAAK, but activates TREK2 (11). Members of the TREK channel subfamily are also regulated extensively by intracellular scaffolding and signaling proteins (10).…”

Optical probing of a dynamic membrane interaction that regulates the TREK1 channel

“…Although the IRK1 channel differs from TREK1 in its selectivity for PI (4,5)P2, it appears to have a common mechanism of channel regulation in that channel activity is enhanced when the IRK1 C terminus associates with the membrane and is reduced when PI(4,5)P2 levels drop and the C terminus dissociates from the membrane. Thus, it appears that dissociation from the membrane of the C terminus of a channel may be a general mechanism of inhibition.…”

“…This current drives the membrane potential toward the K + equilibrium potential and thus affects input resistance. TREK1 displays low basal activity when expressed alone (1) but can be strongly stimulated by temperature (2), mechanical stretch (3), external alkalization (4), intracellular acidification (5), polyunsaturated fatty acids (PUFAs) (6), lysophospholipids (7), phosphatidylinositol-4,5-bisphosphate [PI (4,5)P2] (8,9), and pharmacological agents such as volatile anesthetics (10) and riluzole (11). TREK1 is inhibited by neurotransmitters and hormones that activate Gq and Gs pathways (3,(12)(13)(14) and pharmacological agents such as the antidepressant drug fluoxetine (15).…”

ClC-3 is a candidate of the channel proteins mediating acid-activated chloride currents in nasopharyngeal carcinoma cells

“…Changes of extracellular pH may modulate the activities of ion channels. It has been reported that extracellular acidification inhibited inwardly rectifying potassium channels (11,15,30), mechanosensitive potassium channel (or tandem pore domain potassium channel) TREK1 (25), intracellular calcium-activated potassium channel K Ca 2.2 and K Ca 2.3 (24), the voltage-gated potassium channel Kv1.5 (14), human ether-à-go-go potassium channel (6) and voltage-dependent Ca 2ϩ channel (1), but activated mechanosensitive potassium channel TREK2 (25) and modulated the activities of ATP-sensitive potassium channel (12). The effects of pH changes on ion channels may be related to the protonation of histidine residues in the outer pore regions of channels, which have been reported to be proton interaction sites that regulate channel availability and inactivation (14,24,25).…”