A Novel Mechanism for Human K2P2.1 Channel Gating

Abstract

The mammalian K 2P 2.1 potassium channel (TREK-1, KCNK2) is highly expressed in excitable tissues, where it plays a key role in the cellular mechanisms of neuroprotection, anesthesia, pain perception, and depression. Here, we report that external acidification, within the physiological range, strongly inhibits the human K 2P 2.1 channel by inducing "C-type" closure. We have identified two histidine residues (i.e. His-87 and His-141), located in the first external loop of the channel, that govern the response of the channel to external pH. We demonstrate that these residues are within physical proximity to glutamate 84, homologous to Shaker Glu-418, KcsA Glu-51, and KCNK0 Glu-28 residues, all previously argued to stabilize the outer pore gate in the open conformation by forming hydrogen bonds with poreadjacent residues. We thus propose a novel mechanism for pH sensing in which protonation of His-141 and His-87 generates a local positive charge that serves to draw Glu-84 away from its natural interactions, facilitating the collapse of the selectivity filter region. In accordance with this proposed mechanism, low pH modified K 2P 2.1 selectivity toward potassium. Moreover, the proton-mediated effect was inhibited by external potassium ions and was enhanced by a mutation (S164Y) known to accelerate C-type gating. Furthermore, proton-induced current inhibition was more pronounced at negative potentials. Thus, voltage-dependent C-type gating acceleration by protons represents a novel mechanism for K 2P 2.1 outward rectification.

External Ba2+ Block of the Two-pore Domain Potassium Channel TREK-1 Defines Conformational Transition in Its Selectivity Filter

“…It has been confirmed that the regulation of phosphatidylinositol 4,5-biphosphate to TREK-1 involves alteration of gating patterns (19). Extracellular acid could depress the TREK-1 current by facilitating C-type inactivation, in which conformational modification of the pore region could be involved (20). However, up to now, no clues have been found about how these signals interact with the SF in TREK-1.…”

“…External H ϩ Traps Ba 2ϩ Inside the Selectivity Filter of TREK-1-TREK-1 is very sensitive to external protons, and acidification strongly inhibits the channel via a mechanism resembling C-type inactivation in voltage-dependent potassium channels (20,37). The key property of this mechanism is conformational transition of the SF to the nonconductive state.…”

“…6, B and C, n ϭ 6, p Ͻ 0.001). H126A, a pH-insensitive mutant containing a histidine-to-alanine transition (20,37), was used to eliminate the pH sensitivity of TREK-1. External application of 1 mM Ba 2ϩ still blocked the currents quickly, but the currents of H126A recovered completely from Ba 2ϩ blockade in pH 6.0 external solutions (Fig.…”

A role of stretch-activated potassium currents in the regulation of uterine smooth muscle contraction

“…Moreover, TRAAK-family K2P channels are modulated by cellular lipids and pharmacological agents, including polyunsaturated fatty acids such as arachidonic acid and volatile general anesthetics [42] . Acidity and heat have also been suggested to activate the channel [43,44] , while antipsychotics such as fluphenazine have been shown to block TREK-1 but not the related TRAAK channels [45] .…”

Separate Gating Mechanisms Mediate the Regulation of K2P Potassium Channel TASK-2 by Intra- and Extracellular pH

“…Recently, TREK-1 and TREK-2 have been found to respond also to external proton concentration within the physiological range (10,11), but, remarkably, although TREK-1 is strongly inhibited by extracellular acidification, TREK-2 is activated by acidification (11).…”