Differential phospholipase C‐dependent modulation of TASK and TREK two‐pore domain K⁺ channels in rat thalamocortical relay neurons

Abstract

Key pointsr During the behavioural states of sleep and wakefulness thalamocortical relay neurons fire action potentials in high frequency bursts or tonic sequences, respectively.r The modulation of specific K + channel types, termed TASK and TREK, allows these neurons to switch between the two modes of activity.r In this study we show that the signalling lipids phosphatidylinositol 4,5-bisphosphate (PIP 2 ) and diacylglycerol (DAG), which are components of their membrane environment, switch on and shut off TREK and TASK channels, respectively. r These channel modulations contribute to a better understanding of the molecular basis of the effects of neurotransmitters such as ACh which are released by the brainstem arousal system. r The present report introduces PIP 2 and DAG as new elements of signal transduction in the thalamus. AbstractThe activity of two-pore domain potassium channels (K 2P ) regulates the excitability and firing modes of thalamocortical (TC) neurons. In particular, the inhibition of two-pore domain weakly inwardly rectifying K + channel (TWIK)-related acid-sensitive K + (TASK) channels and TWIK-related K + (TREK) channels, as a consequence of the stimulation of muscarinic ACh receptors (MAChRs) which are coupled to phosphoinositide-specific phospholipase C (PLCβ), induces a shift from burst to tonic firing. By using a whole cell patch-clamp approach, the contribution of the membrane-bound second messenger molecules phosphatidylinositol 4,5-bisphosphate (PIP 2 ) and diacylglycerol (DAG) acting downstream of PLCβ was probed. The standing outward current (I SO ) was used to monitor the current through TASK and TREK channels in TC neurons. By exploiting different manoeuvres to change the intracellular PIP 2 level in TC neurons, we here show that the scavenging of PIP 2 (by neomycin) results in an increased muscarinic effect on I SO whereas increased availability of PIP 2 (inclusion to the patch pipette; histone-based carrier) decreased muscarinic signalling. The degree of muscarinic inhibition specifically depends on phosphatidylinositol phosphate (PIP) and PIP 2 but no other S. G. Meuth and T. Budde contributed equally to this work. phospholipids (phosphatidic acid, phosphatidylserine). The use of specific blockers revealed that PIP 2 is targeting TREK but not TASK channels. Furthermore, we demonstrate that the inhibition of TASK channels is induced by the application of the DAG analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG). Under current clamp conditions the activation of MAChRs and PLCβ as well as the application of OAG resulted in membrane depolarization, while PIP 2 application via histone carrier induced a hyperpolarization. These results demonstrate a differential role of PIP 2 and DAG in K 2P channel modulation in native neurons which allows a fine-tuned inhibition of TREK (via PIP 2 depletion) and TASK (via DAG) channels following MAChR stimulation.

Inhibition of TREK-2 K+ channels by PI(4,5)P2: an intrinsic mode of regulation by intracellular ATP via phosphatidylinositol kinase

“…Based on the prevention of ATPinduced I TREK-2,i-o suppression by PI-kinase inhibitors (wortmannin or LY29402) and the inhibition by PI(4,5)P 2 [16,27,36], we proposed that TREK-2 inhibition by intracellular ATP is mediated by membrane-delimited production of PI(4,5)P 2 . However, our model of tonic intrinsic inhibition of TREK-2 by PI(4,5)P 2 has not yet been confirmed by other researchers.…”

“…In subsequent reviews, Chemin et al demonstrated that PI(4,5)P 2 inhibited TREK-1 in about half of i-o patches on COS-7 cells and hippocampal neurons [3,5]. Nevertheless, most relevant studies and reviews by other researchers regard PI(4, 5)P 2 as a stimulatory factor of TREKs [2,11,30,31,33].…”

“…Although we studied TREK-2 endogenously expressed in B lymphocytes and stably overexpressed in HEK293 cells, studies of TREK-1 by other researchers have generally used transiently transfected COS-7 cells [4], hippocampal neurons [5], sympathetic ganglion neurons [30], or thalamocortical neurons [2]. Another possible source of discrepancies is that different channel subtypes were investigated, i.e., TREK-1 vs. TREK-2.…”

TASK, TREK & Co.: a mutable potassium channel family for diverse tasks in the brain

“…However, DAG could be identified as TASK-channel inhibitor in further experiments with heterologously expressed channels in which genetic sensors for PIP 2 and DAG have been used. These results could be recently confirmed in native neurons [21]. In this context, the signalling lipids, DAG and PIP 2 are obviously components of the membrane environment in which TASK-and TREK-channels are embedded.…”

“…It could be demonstrated through the combination of electrophysiological and molecular biological techniques that TASK-1-, TASK-3-, and TREK-1-channels underlie this adjustable potassium-leak conductance in relay neurons [17][18][19][20][21]. Moreover, inhalation anaesthetics like halothane and isoflurane induce a hyperpolarization of relay neurons by activating K 2P -channels which is accompanied by increased burst activity [22].…”