Interactive reportLocalization of the tandem pore domain K+ channel KCNK5 (TASK-2) in the rat central nervous system☆
Introduction
Ion channels that selectively pass potassium (K+) ions represent the largest family of ion channels. K+ channels play a role in the control of electrical responses in the central nervous system (CNS). They set and modulate the membrane potential, shape action potentials and regulate their frequencies, thus controlling neuronal firing and neurotransmitter release. K+ channels are organized into three main superfamilies according to their membrane topology. The largest superfamily comprises subunits with six transmembrane segments and one pore domain (for review, see Ref. [26]). The second superfamily comprises subunits with only two transmembrane segments and one pore domain (for reviews, see Refs. [20], [27]). The K+ channel subunits of these extensively characterized two superfamilies assemble as tetramers to form functional K+ channels [34], [60] and are further organized into families and subfamilies including the voltage-gated K+ channels, Ca2+-dependent K+ channels, ATP-sensitive K+ channels, G protein-coupled K+ channels, and inward-rectifying K+ channels. The third superfamily of K+ channel subunits was only recently discovered [21]. Mammalian members of this new class of K+ channels are comprised of subunits with four transmembrane segments and the unique feature of two pore domains in tandem [29]. This structural organization gave the new superfamily its name, i.e. tandem pore domain K+ channels (2P K+ channels). 2P K+ channels are also named KCNKx channels according to the Human Genome Organization Nomenclature Committee (HUGO; for more information see http://www.gene.ucl.ac.uk/nomenclature/). At present, 14 human 2P K+ channels have been identified [6], [10], [11], [15], [29], [32], [33], [42], [45], [46], [47], [50], [56], but functional expression has only been reported for eleven human 2P K+ channels (for reviews, see Refs. [16], [41]). 2P K+ channels are the most numerous K+ channels in both Caenorhabditis elegans [1], [58] and Drosophila melanogaster [49] genomes and data from the human genome sequencing program lead to the theoretical extrapolation that there may be more than 20 2P K+ channel genes expressed in humans [31]. Because 2P K+ channels are not gated by voltage, are non-inactivating, are resistant to classical K+ channel blockers, and pass currents over a wide range of voltages predicted by the Goldman–Hodgkin–Katz equation, they closely resemble physiological baseline K+ channels and are therefore believed to be the independent molecular entities of the long sought after K+ leak conductances [3], [19].
TASK-1, the TWIK-related acid-sensitive K+ channel, is the most extensively studied 2P K+ channel. Native baseline K+ currents resembling TASK-1 have been described in atrial cells [22], a human neuroepithelial body-derived cell line [40], carotid body type-I cells [4], adrenal glomerulosa cells [9], and cerebellar granule cells [39]. Recently, it has been shown that neurotransmitter modulation of TASK-1 is an important mechanism in the short and even long-term regulation of neuronal excitability. Interactions between TASK-1 and the thyrotropin-releasing hormone receptor 1 in hypoglossal motoneurons [55] and between TASK-1 and the γ-aminobutyric acid type A receptor (GABAA) in cerebellar granule cells have been described [2]. In addition, activation of TASK-1 currents in central motoneurons and locus coeruleus neurons by volatile anesthetics suggests that TASK-1 may represent a molecular substrate for their clinical effects [52].
Despite sharing less than 30% amino acid identity in their sequences, TASK-2 has many physiological and pharmacological properties in common with TASK-1, such as the distinct sensitivity to changes in extracellular and intracellular acidity and activation by volatile anesthetics [11], [17], [28], [47]. However, there is much less information available about the functional role and expression pattern of TASK-2 compared with TASK-1. An mRNA distribution analysis reports the strongest expression of TASK-2 in human liver, kidney, and pancreas [38]. Previous studies in kidney localize TASK-2 to the cortical distal tubules and collecting ducts [47] and the proximal convoluted tubules [44]. However, the signals from native K+ channels recorded from cortical collecting tubules do not resemble the biophysical and pharmacological properties of those from TASK-2 [14], [57]. Although TASK-2 mRNA was not detected by Northern blot analysis and reverse transcription polymerase chain reactions (RT-PCR) in the human CNS with the exception of spinal cord [17], [38], RT-PCR analysis from mouse and rat tissues showed TASK-2 mRNA in cortex, cerebellum, and brain stem [17], [47].
In general, the function of K+ channels is determined by differences in their electrophysiological properties and modulation as well as by their expression pattern in different cell types. While an mRNA distribution analysis of all 2P K+ channels has recently been published [38], only limited data on the tissue distribution of 2P K+ channel proteins are available [7], [18], [24], [36], [48]. Interpretation of tissue distribution results of 2P K+ channels is further complicated by known cross-species and developmental differences [2], [24]. In this study we describe the immunohistochemical localization of TASK-2, previously cloned from human kidney [47], in the rat central nervous system at the cellular level with the aim of better understanding its expression, distribution, and function.
Section snippets
Western blots
Anti-TASK-2, affinity purified polyclonal antibodies raised in rabbit against the polypeptide corresponding to the amino acid residues 483–499 of the C-terminal (from tyrosine 483 to threonine 499) of human TASK-2 (hTASK483–499), were used (Alomone Laboratories, Jerusalem, Israel). The epitope is specific for TASK-2 and is not present in any other protein (BLASTp). For Western blots, protein extracts from rat cultured cerebellar granule and glial cells and rat kidney were prepared with a Triton
Results
Anti-TASK-2 antibodies recognized by Western blot analysis a strong band with the molecular weight of ∼58 kDa of protein extracted from rat kidney and from cultured rat cerebellar granule and glial cells (Fig. 1). The level of TASK-2 expression is higher in kidney than in the cultured nervous tissue. The size of the band is in close agreement with the previously reported molecular weight of TASK-2 [17], [47]. Since previous studies demonstrated abundant TASK-2 mRNA expression in human kidney
Discussion
TASK-2 mRNA expression is reported to be abundant in human kidney, liver, and pancreas [47], but low or even absent in mouse or human brain [17], [38], [47]. In agreement with these previous results and the immunoblot shown in Fig. 1, TASK-2 immunocytochemical protein expression levels were also weaker in rat brain compared with rat kidney (Fig. 2). As previously shown with in situ hybridization [47] and primary cultures [44], in the kidney TASK-2 is mainly expressed in renal tubules.
In
Acknowledgements
This research was supported from NIH grants GM-58149 (CSY) and GM-57529 (BDW). The authors thank Dr Igor Mitrovic, Department of Anatomy and Physiology UCSF, for his advice and support with immunohistochemistry, Dr Pamela Pierce Palmer, Department of Anesthesia and Perioperative Care UCSF, for financial and technical support, and Joan Etlinger, Department of Anesthesia, University of Basel, for editorial assistance.
References (60)
- et al.
Cloning, localisation and functional expression of a novel human, cerebellum specific, two pore domain potassium channel
Mol. Brain Res.
(2000) - et al.
TWIK-2, a new weak inward rectifying member of the tandem pore domain potassium channel family
J. Biol. Chem.
(1999) - et al.
Anesthetic actions within the spinal cord: contributions to the state of general anesthesia
Trends Neurosci.
(1995) - et al.
Characterization of TASK-4, a novel member of the pH-sensitive, two-pore domain potassium channel family
FEBS Lett.
(2001) - et al.
Genomic and functional characteristics of novel human pancreatic 2P domain K(+) channels
Biochem. Biophys. Res. Commun.
(2001) - et al.
Distribution and expression of TREK-1, a two-pore-domain potassium channel, in the adult rat CNS
Neuroscience
(2001) - et al.
TASK-3, a new member of the tandem pore K+ channel family
J. Biol. Chem.
(2000) - et al.
Localization of the tandem pore domain K+ channel TASK-1 in the rat central nervous system
Mol. Brain Res.
(2000) - et al.
The structure, function and distribution of the mouse TWIK-1 K+ channel
FEBS Lett.
(1997) - et al.
Cloning and expression of human TRAAK, a polyunsaturated fatty acids-activated and mechano-sensitive K(+) channel
FEBS Lett.
(2000)
Human TREK-2, a 2P domain mechano-sensitive K+ channel with multiple regulations by polyunsaturated fatty acids, lysophospholipids, and Gs, Gi, and Gq protein-coupled receptors
J. Biol. Chem.
TRAAK is a mammalian neuronal mechano-gated K+ channel
J. Biol. Chem.
Distribution analysis of human two pore domain potassium channels in tissues of the central nervous system and periphery
Mol. Brain Res.
Properties and modulation of mammalian 2P domain K+ channels
Trends Neurosci.
THIK-1 and THIK-2, a novel subfamily of tandem pore domain K+ channels
J. Biol. Chem.
TASK-3, a novel tandem pore-domain acid-sensitive K+ channel: an extracellular histidine as pH sensor
J. Biol. Chem.
Cloning and expression of a novel pH-sensitive two pore domain K+ channel from human kidney
J. Biol. Chem.
Cloning of a new mouse two-P domain channel subunit and a human homologue with a unique pore structure
J. Biol. Chem.
Mechanisms of halothane action on synaptic transmission in motoneurons of the newborn rat spinal cord in vitro
Brain Res.
TASK-1, a two pore domain K+ channel, is modulated by multiple neurotransmitters in motoneurons
Neuron
Pentobarbital and halothane hyperpolarize cat alpha-motoneurons
Brain Res.
Determination of the subunit stoichiometry of an inwardly rectifying potassium channel
Neuron
Neurobiology of the Caenorhabditis elegans genome
Science
Adaptive regulation of neuronal excitability by a voltage-independent potassium conductance
Nature
Neurobiology: the acid test for resting potassium channels
Curr. Biol.
An oxygen-, acid- and anaesthetic-sensitive TASK-like background potassium channel in rat arterial chemoreceptor cells
J. Physiol.
Expression of TWIK-1, a novel weakly inward rectifying potassium channel in rat kidney
Am. J. Physiol.
TASK (TWIK-related acid-sensitive K+ channel) is expressed in glomerulosa cells of rat adrenal cortex and inhibited by angiotensin II
Mol. Endocrinol.
TASK, a human background K+ channel to sense external pH variations near physiological pH
EMBO J.
Hypothesis: inhaled anesthetics produce immobility and amnesia by different mechanisms at different sites
Anesth. Analg.
Cited by (54)
Chloride Dysregulation, Seizures, and Cerebral Edema: A Relationship with Therapeutic Potential
2017, Trends in NeurosciencesCitation Excerpt :RVI promotes Na+, K+, Cl−, and water accumulation via NKCC1 (as well as Na+/H+ and Cl−/HCO3− transporters), and thereafter leads to the production of idiogenic osmoles (e.g., inositol, betaine, etc.) if the osmotic perturbation persists [103]. In cell swelling, RVD triggers the acute loss of cytoplasmic K+, Cl−, and water by the K+/Cl− cotransporters, the TASK-2 K+ channel [104,105], and the volume-regulated anion channel composed of LRRC8 heteromers [106–111]. In addition to the loss of inorganic ions, RVD also triggers the loss of non-essential organic osmolytes, and this might also be mediated by LRRC8 channels [112].
Identification of potassium and chloride channels in eccrine sweat glands
2016, Journal of Dermatological ScienceRole of leak potassium channels in pain signaling
2015, Brain Research BulletinCitation Excerpt :The weak expression of TASK2 channels has been found in the brain (Reyes et al., 1998; Gestreau et al., 2010). TASK2 immunoreactivity was found in the superficial layers of spinal cord and small-diameter neurons of DRG (Gabriel et al., 2002). These findings suggest that TASK2 channels are involved in central mechanisms for controlling neuronal excitability and in peripheral signal transduction.
Novel TASK channels inhibitors derived from dihydropyrrolo[2,1-a] isoquinoline
2014, Neuropharmacology
- ☆
Published on the World Wide Web on 7 December 2001.