TASK-3, a New Member of the Tandem Pore K+ Channel Family

Abstract

We have isolated from the rat cerebellum cDNA library a complementary DNA encoding a new member of the tandem pore K ؉ channel family. Its amino acid sequence shares 54% identity with that of TASK-1, but less than 30% with those of TASK-2 and other tandem pore K ؉ channels (TWIK, TREK, TRAAK). Therefore, the new clone was named TASK-3. Reverse transcriptase-polymerase chain reaction analysis showed that TASK-3 mRNA is expressed in many rat tissues including brain, kidney, liver, lung, colon, stomach, spleen, testis, and skeletal muscle, and at very low levels in the heart and small intestine. When expressed in COS-7 cells, TASK-3 exhibited a time-independent, noninactivating K ؉ -selective current. Single-channel conductance was 27 pS at ؊60 mV and 17 pS at 60 mV in symmetrical 140 mM KCl. TASK-3 current was highly sensitive to changes in extracellular pH (pH o ), a hallmark of the TASK family of K ؉ channels. Thus, a change in pH o from 7.2 to 6.4 and 6.0 decreased TASK-3 current by 74 and 96%, respectively. Mutation of histidine at position 98 to aspartate abolished pH o sensitivity. TASK-3 was blocked by barium (57%, 3 mM), quinidine (37%, 100 M), and lidocaine (62%, 1 mM). Thus, TASK-3 is a new member of the acidsensing K ؉ channel subfamily (TASK).Potassium (K ϩ ) channels are involved in a variety of cellular functions including regulation of neuronal firing rate, heart rate, muscle contraction, and hormone secretion. Mammalian K ϩ channels can now be grouped into three main structural classes with each subunit possessing two, four, or six transmembrane segments (1-3). A structurally different K ϩ channel having eight transmembrane segments has been cloned from yeast (4 -6), but a similar channel subunit has not been identified in the mammalian system. Despite the structural diversity, all K ϩ channel subunits share a conserved P domain that is essential for providing K ϩ selectivity (7-9). In Caenorhabditis elegans, ϳ50 putative K ϩ channels subunits possessing two pore-forming domains and four transmembrane segments (2P/ 4TM) 1 have been identified by searching the genome sequences (10, 11). Recent cloning efforts have led to the identification of several members of the 2P/4TM K ϩ channels. Open rectifier K ϩ channel (ORK1) from Drosophila melanogaster and tandem of P domains in a weak inward rectifying K ϩ channel (TWIK-1) from human kidney were the first two members of this family to be cloned (12, 13). Recent studies now indicate that TWIK-1 does not form a functional ion channel, whereas the open rectifier K ϩ channel 1 does (14, 15). Subsequently, other members of this family were cloned using expressed sequence tags identified by searching the GenBank TM data base for TWIK-1-like sequences or using degenerate primers designed to amplify a DNA fragment with sequences homologous to TWIK-1. Electrophysiological studies of 4TM K ϩ channels suggest that most behave as background K ϩ currents (ORK1, TASK, TREK, TRAAK), although some have additional properties such as sensitivity to mechanical stretch, fr...

Functional Expression of TRESK-2, a New Member of the Tandem-pore K+ Channel Family

“…Quinidine, a nonspecific blocker of many K ϩ channels (including those of K 2P channels), strongly inhibits TRESK-1 and TRESK-2. The inhibitory effect of arachidonic acid on TRESK-2 is similar to those observed with TASK-1 and TASK-3, although the physiological significance of such inhibition is not yet known (12,28). It is clear from these findings that the pore properties of many K 2P channels, including TRESK-2, are different from those of voltagegated (Kv) and inwardly rectifying (Kir) K ϩ channels that are highly sensitive to Ba 2ϩ and tetraethylammonium, which block the channels by entering the permeation pathway.…”

sup-9, sup-10, andunc-93May Encode Components of a Two-Pore K+Channel that Coordinates Muscle Contraction inCaenorhabditis elegans

“…Mammalian TASK-1 and TASK-3 form a subfamily of two-pore K ϩ channels that are activated by high pH, volatile anesthetics, and neurotransmitters (Duprat et al, 1997;Leonoudakis et al, 1998;Patel et al, 1999;Kim et al, 2000;Millar et al, 2000;Rajan et al, 2000;Talley et al, 2000). Our findings indicate that UNC-93 and SUP-10 associate with a SUP-9 two-pore K ϩ channel and suggest that UNC-93 and SUP-10 may be regulatory subunits of this channel.…”

The Impact of Heterozygous KCNK3 Mutations Associated With Pulmonary Arterial Hypertension on Channel Function and Pharmacological Recovery

“…KCNK9 is thought to be co‐expressed with KCNK3 in various tissues outside of the lung, including in the central nervous system, heart, and adrenal glands, and functional heterodimerization of KCNK3 with KCNK9 in multiple tissues has already been studied 6, 11, 12, 13, 175.…”

“…Adding to the complexity of KCNK3 regulation, the closely related acid‐sensitive KCNK9 channel dimerizes with KCNK3, forming KCNK9‐KCNK3 heterodimeric channels in tissues where both channels are expressed 11, 12, 13, 14, 15. KCNK9 is more maximally activated at pH 7.4 than KCNK3 16, 17. The channels are co‐expressed in a variety of tissues, promoting tissue‐specific diversity of channel function.…”