Investigation of Molecular Diversity of ATP-Sensitive K^+ Channels.

ATP敏感的K^+ (K_<ATP>)通道代表了细胞内ATP抑制的K^+通道家族，已在多种组织中发现，包括心脏，胰腺β细胞，骨骼肌，平滑肌和中枢神经系统。这些K_<ATP>通道与多种细胞功能密切相关，如在心脏代谢抑制过程中发生的动作电位持续时间缩短和K +离子的细胞损失、胰腺β细胞分泌胰岛素、平滑肌松弛、骨骼肌兴奋性调节和神经递质释放。此外，NDP、pH、Mg^<2+>、多胺、PIP_2、G蛋白、K^+通道开放剂和磺脲类等多种因子也能调节K_<ATP>通道的活性。K_<ATP>通道由两种膜蛋白Kir6组成。x和SURx。我们用膜片钳技术表征了K_<ATP>通道在哺乳动物细胞系中表达的不同亚基组合重组。结果如下所示；1) Kir6.2和SUR2A对K_<ATP>通道的活性与心脏K_<ATP>通道的活性基本相同。2) Kir6.1和Kir6.2的自发开孔和统一电导分别由两个假定的跨膜区域之间的N端和c端以及细胞外连接域的一部分决定。3)在C端发散的SUR2A和SUR2B的剪接异构体对K^+通道打开剂和磺酰脲的敏感性不同。4)虽然SUR亚基含有K^+通道打开剂和细胞内核苷酸的关键结合位点，但Kir亚基似乎影响了整个SUR/Kir功能通道复合物对这些化合物的反应方式。

ATP-sensitive K^+ (K_<ATP>) channels, which represent a family of K^+ channels inhibited by intracellular ATP, have been found in a variety of tissues including heart, pancreatic beta-cells, skeletal muscle, smooth muscle, and the central nervous system.These K_<ATP> channels are closely related to diverse cellular functions, such as shortening of action potential duration and cellular loss of K^+ ions that occur during metabolic inhibition in heart, insulin secretion from pancreatic beta-cells, smooth muscle relaxation, regulation of skeletal muscle excitability, and neurotransmitter release.Furthermore, other diverse factors such as NDP, pH, Mg^<2+>, polyamine, PIP_2, G proteins, K^+ channel openers and sulfonylurea also modulate the activity of K_<ATP> channels.K_<ATP> channel is composed of two kinds of membrane proteins Kir6.x and SURx.We characterized K_<ATP> channels reconstituted with various combination of subunits expressed in mammalian cell line with patch clamp techniques.The result runs as follows ; 1) The activity of K_<ATP> channel with Kir6.2 and SUR2A is almost same as that of cardiac K_<ATP> channel.2) Spontaneous openings and unitary conductances of Kir6.1 and Kir6.2 are determined with a part of each N- and C-terminus and extracellular linker domain between the two putative membrane-spanning regions, respectively.3) Splicing isoforms of SUR2A and SUR2B which are divergent at C terminus have different sensitivities to both K^+ channel openers and sulfonylurea.4) Although SUR subunits contain the critical binding sites for K^+ channel openers and intracellular nucleotides, the Kir subunits seem to influence the way in which the entire SUR/Kir functional channel complex reacts to these compounds.