Kim Y, Bang H, Kim D
Department of Physiology and Biophysics, Finch University of Health Sciences/The Chicago Medical School, North Chicago, Illinois 60064, USA.
J Biol Chem. 2000 Mar 31;275(13):9340-7. doi: 10.1074/jbc.275.13.9340.
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 microM), and lidocaine (62%, 1 mM). Thus, TASK-3 is a new member of the acid-sensing K(+) channel subfamily (TASK).
我们从大鼠小脑cDNA文库中分离出了一个编码串联孔道K⁺通道家族新成员的互补DNA。其氨基酸序列与TASK-1的氨基酸序列有54%的同一性，但与TASK-2及其他串联孔道K⁺通道（TWIK、TREK、TRAAK）的氨基酸序列同一性低于30%。因此，这个新克隆被命名为TASK-3。逆转录聚合酶链反应分析表明，TASK-3 mRNA在大鼠的许多组织中都有表达，包括脑、肾、肝、肺、结肠、胃、脾、睾丸和骨骼肌，而在心脏和小肠中的表达水平非常低。当在COS-7细胞中表达时，TASK-3表现出一种与时间无关、不发生失活的K⁺选择性电流。在对称的140 mM KCl中，单通道电导在-60 mV时为27 pS，在60 mV时为17 pS。TASK-3电流对细胞外pH（pH(o)）的变化高度敏感，这是TASK家族K⁺通道的一个标志。因此，pH(o)从7.2变为6.4和6.0时，TASK-3电流分别下降了74%和96%。将第98位的组氨酸突变为天冬氨酸消除了pH(o)敏感性。TASK-3被钡（57%，3 mM）、奎尼丁（37%，100 microM）和利多卡因（62%，1 mM）阻断。因此，TASK-3是酸敏感K⁺通道亚家族（TASK）的一个新成员。
