A new member of the tandem-pore K ؉ (K 2P ) channel family has been isolated from mouse testis complementary DNA. The new K 2P channel was named TRESK-2, as its amino acid sequence shares 65% identity with that of TRESK-1. Mouse TRESK-2 is a 394-amino acid protein and possesses four putative transmembrane segments and two pore-forming domains. TRESK-2 has a long cytoplasmic domain joining the second and third transmembrane segments and a short carboxyl terminus. In the rat, TRESK-2 mRNA transcripts were expressed abundantly in the thymus and spleen and at low levels in many other tissues, including heart, small intestine, skeletal muscle, uterus, testis, and placenta, as judged by Northern blot analysis. TRESK-2 mRNA was also expressed in mouse and human tissues. In COS-7 cells transfected with TRESK-2 DNA, a time-independent and noninactivating K ؉ -selective current was recorded. TRESK-2 was insensitive to 1 mM tetraethylammonium, 100 nM apamin, 1 mM 4-aminopyridine, and 10 M glybenclamide. TRESK-2 was inhibited by 10 M quinidine, 20 M arachidonate and acid (pH 6.3) at 49, 43, and 23%, respectively. Single channel openings of TRESK-2 showed marked open channel noise. In symmetrical 150 mM KCl, the current-voltage relationship of TRESK-2 was slightly inwardly rectifying, with the single channel conductance 13 picosiemens (pS) at ؉60 mV and 16 pS at ؊60 mV. In inside-out patches, TRESK-2 was unaffected by the intracellular application of 10 M guanosine 5 -O-(thiotriphosphate). These results show that TRESK-2 is a functional member of the K 2P channel family and contributes to the background K ؉ conductance in many types of cells.Mammalian potassium channels are divided into three structural classes based on the number of predicted transmembrane (TM) 1 segments (two, four, or six) and pore-forming (P) domains (one or two). Searching the DNA data base for sequences homologous to previously cloned K ϩ channels led to identification of the class now referred to as tandem-pore or two-pore domain K ϩ (K 2P ) channels (1-4). Each subunit of a K 2P channel possesses four TM segments and two P domains, and therefore two subunits are thought to assemble to form a functional dimeric K ϩ channel (4, 5). K 2P channels can be divided into six subfamilies based on amino acid homology: TWIK-1 and TWIK-2 (6 -9); THIK-1 and THIK-2 (10); TASK-1, TASK-3, and TASK-5 (11-13); TALK-1, TASK-2, and TALK-2 (14 -16); TREK-1, TREK-2, and TRAAK (17-20); and TRESK-1 (21). Many of these K 2P channel are able to form functional K ϩ channels when expressed in oocytes or mammalian cells. Those K 2P channels that form functional K ϩ channels exhibit interesting electrophysiological and pharmacological properties. For example, TASK-1 and TASK-3 are active at rest, highly sensitive to extracellular pH and oxygen concentration (22), and activated by volatile anesthetics (23, 24). TREK-1 and TREK-2 are activated by free fatty acids, protons, increased membrane tension, heat, and volatile anesthetics (25, 26). These channels are functionally expressed...
