Roberds S L, Tamkun M M
Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232.
Proc Natl Acad Sci U S A. 1991 Mar 1;88(5):1798-802. doi: 10.1073/pnas.88.5.1798.
Five distinct K+ channel cDNA molecules (RK1 to RK5) were cloned from either rat heart or rat aorta cDNA libraries. Four of the channels, RK1 to RK4, are similar or identical to Shaker-like K+ channels previously identified in rat brain cDNA libraries. Major differences among RK1 to RK4 exist in the amino- and carboxyl-terminal regions and in amino acids representing potential extracellular sequence between the S1 and S2 hydrophobic domains. RK5 encodes a unique channel of 490 amino acids having six hydrophobic domains but only five basic residues in the putative voltage-sensing domain. Unlike RK1 to RK4, RK5 is a rat homologue of the Drosophila Shal family of K+ channels, which have not been previously described in mammals. Although RK5 mRNA is present in cardiac atrium and ventricle, it is most abundant in brain. RK1, RK2, and RK3 transcripts are predominantly found in brain but are present also at lower levels in other tissues, such as heart and aorta. RK2 is absent from skeletal muscle whereas RK1 and RK3 are present in this tissue. RK4 mRNA is ubiquitous in electrically excitable tissue, being present at comparable levels in atrium, ventricle, aorta, brain, and skeletal muscle. The cloning of RK5 confirms the presence in mammals of all four Drosophila K+ channel families: Shaker, Shab, Shaw, and Shal.
从大鼠心脏或大鼠主动脉cDNA文库中克隆出了5种不同的钾离子通道cDNA分子（RK1至RK5）。其中4种通道，即RK1至RK4，与先前在大鼠脑cDNA文库中鉴定出的类Shaker钾离子通道相似或相同。RK1至RK4之间的主要差异存在于氨基末端和羧基末端区域，以及S1和S2疏水结构域之间代表潜在细胞外序列的氨基酸中。RK5编码一个由490个氨基酸组成的独特通道，具有6个疏水结构域，但在假定的电压感应结构域中只有5个碱性残基。与RK1至RK4不同，RK5是果蝇Shal家族钾离子通道的大鼠同源物，此前在哺乳动物中尚未有过描述。尽管RK5 mRNA存在于心房和心室中，但在脑中最为丰富。RK1、RK2和RK3转录本主要存在于脑中，但在其他组织如心脏和主动脉中也有较低水平的表达。骨骼肌中不存在RK2，而RK1和RK3存在于该组织中。RK4 mRNA在可兴奋组织中普遍存在，在心房、心室、主动脉、脑和骨骼肌中的表达水平相当。RK5的克隆证实了哺乳动物中存在果蝇所有4个钾离子通道家族：Shaker、Shab、Shaw和Shal。
