The significance of Gprotein-gated inwardly rectifying K^+ channel in the anterior pituitary endcrine cells

G蛋白门控内向整流K+(K_G)通道是由百日咳毒素敏感的G蛋白直接激活的内向整流性K~+通道的一员。在内分泌器官，即垂体前叶，报道了一些神经递质，包括多巴胺和生长抑素，通过激活K_G通道使膜超极化，从而抑制激素的分泌。我们发现K_G通道的主要亚基GIRK1(Kir3.1)主要定位于含有促甲状腺激素的细胞内致密核心囊泡的细胞膜上。这些甲状腺细胞在三联释放激素的刺激下，引起囊泡与质膜的融合，质膜GIRK1亚基表达增加，多巴胺和生长抑素刺激的K_G电流明显增强，提示了一种新的机制，即功能离子通道快速插入质膜，从而形成内分泌系统激素分泌的新型负反馈控制环。

G protein-gated inwardly rectifying K+ (K_G) channel, a member of inwardly rectifying K^+ channel, is directly activated by pertussis toxin-sensitive G proteins.In endocrine organs, i.e., the anterior pituitary lobe, it was reported that some neurotransmitters including dopamine and somatostatin hyperpolarize the membrane by activating K_G channels, which results in the inhibition of hormone secretion.We found GIRK1 (Kir3.1), the main subunit of K_G channels, to be localized predominantly on the membranes of intracellular dense core vesicles which contained thyrotropin.Stimulation of these thyrotroph cells with thyrotrpin-releasing-hormone provoked fusion of vesicles to the plasma membrane, increased expression of GIRK1 subunit in the plasma membrane, and markedly enhanced K_G currents stimulated by dopamine and somatostatin.These data indicate a novel mechanism for the rapid insertion of functional ion channels into the plasma membrane, which could form a new type of negative feedback control loop for hormone secretion in the endocrine system.