TRESK two‐pore‐domain K⁺ channels constitute a significant component of background potassium currents in murine dorsal root ganglion neurones

Abstract

TRESK (TWIK-related spinal cord K + channel) is the most recently identified member of the two-pore-domain potassium channel (K 2P ) family, the molecular source of background potassium currents. Human TRESK channels are not affected by external acidification. However, the mouse orthologue displays moderate pH dependence isolated to a single histidine residue adjacent to the GYG selectivity filter. In the human protein, sequence substitution of tyrosine by histidine at this critical position generated a mutant that displays almost identical proton sensitivity compared with mouse TRESK. In contrast to human TRESK, which is specifically located in spinal cord, we detected mouse TRESK (mTRESK) mRNA in several epithelial and neuronal tissues including lung, liver, kidney, brain and spinal cord. As revealed by endpoint and quantitative RT-PCR, mTRESK channels are mainly expressed in dorsal root ganglia (DRG) and on the transcript level represent the most important background potassium channel in this tissue. DRG neurones of all sizes were labelled by in situ hybridizations with TRESK-specific probes. In DRG neurones of TRESK[G339R] functional knock-out (KO) mice the standing outward current IK so was significantly reduced compared with TRESK wild-type (WT) littermates. Different responses to K 2P channel regulators such as bupivacaine, extracellular protons and quinidine corroborated the finding that approximately 20% of IK so is carried by TRESK channels. Unexpectedly, we found no difference in resting membrane potential between DRG neurones of TRESK[WT] and TRESK[G339R] functional KO mice. However, in current-clamp recordings we observed significant changes in action potential duration and amplitude of after-hyperpolarization. Most strikingly, cellular excitability of DRG neurones from functional KO mice was significantly augmented as revealed by reduced rheobase current to elicit action potentials. Background (leak) potassium currents substantially contribute to the resting membrane potential of several excitable and non-excitable cells. This K + conductance plays an important role in setting the cellular excitability and regulates the firing rate of neurones. Two-poredomain potassium (K 2P ) channels, when expressed in heterologous systems, show constitutive activity throughout the physiological range of membrane potential and thus are classified as background K + channels. Functional K 2P channels consist of two subunits, each of which has two pore domains and four transmembrane segments. In mammals 15 different K 2P channel subunits (KCNK) have been identified and, due to structural and functional characteristics, they are divided into several subfamilies, e.g. acid-sensitive TASK channels and lipid-sensitive mechano-gated TREK/TRAAK channels (reviewed by Goldstein et al. 2001;Bayliss et al. 2003; Honoré, 2007). The activity of K 2P channels is regulated by various physical and chemical stimuli such as temperature , membrane stress (Maingret et al. 1999), protons (Duprat et al. 1997Rajan et al. 2000), free fat...

Pungent agents from Szechuan peppers excite sensory neurons by inhibiting two-pore potassium channels

“…Indeed, among sanshool-sensitive KCNK subtypes, KCNK18 contributes significantly to the background K + current in cultured DRG neurons 20 . Moreover, in situ hybridization histochemistry suggests that KCNK18 transcripts are expressed by a significant fraction of primary sensory neurons 21 . However, this analysis is likely to overestimate the prevalence of KCNK18 expression because of the high sequence conservation among KCNK subtypes, with consequent hybridization of in situ probes to numerous KCNK transcripts.…”

“…Thus, we conclude that KCNK channels are the likely targets of sanshool action. Indeed, members of this two-pore K + channel subfamily (KCNK2, KCNK3, KCNK9, KCNK10 and KCNK18) have been proposed to set the resting membrane potential of primary afferent sensory neurons, with KCNK18 (TRESK) having the predominant role [19][20][21] .…”

TREK2 Expressed Selectively in IB4-Binding C-Fiber Nociceptors Hyperpolarizes Their Membrane Potentials and Limits Spontaneous Pain

“…The first is TREK2, which may well contribute Ͼ10 mV (above). Other candidates are other K2Ps (TRESK is in all sizes of DRG neurons) (Dobler et al, 2007;Yoo et al, 2009), Cl Ϫ channels (Mayer, 1985), and voltage-dependent K ϩ currents (such as Kv7.2/7.5 or K ATP ). The last group were reported to contribute very little (Ͻ1.3%) normally to the resting K ϩ -standing current at 37°C (Kang and Kim, 2006), although their contribution would increase with greater depolarization.…”

“…Cl Ϫ channels and voltage-sensitive K ϩ channels (e.g., M-current and/or K ATP ) may contribute to their Ems (Kawano et al, 2009;Rose et al, 2011). However, Kang and Kim (2006) showed that at 37°C TREK2 contributed ϳ69% of the K ϩ standing current (responsible for the majority of Em) in a third of small-sized cultured neonatal rat DRG neurons; TRESK, expressed in all sizes of DRG neurons (Dobler et al, 2007), contributed 16% and TREK1 12%. The relatively high TREK2 mRNA in rat DRGs (Marsh et al, 2012) supports TREK2 contributing substantially to Em in adult DRG neurons.…”

Migraine in the era of precision medicine

“…Overexpression of TRESK in DRG neurons attenuates nerve injury-induced mechanical allodynia (68). The TRESK channel presents perhaps the best opportunity for development of antimigraine therapeutics, given its predicted role in controlling neuronal excitability (69).…”