Light D B, Ausiello D A, Stanton B A
Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire 03756.
J Clin Invest. 1989 Jul;84(1):352-6. doi: 10.1172/JCI114162.
We examined whether GTP binding proteins (G proteins) regulate sodium conducting channels in the apical membrane of renal inner medullary collecting duct (IMCD) cells and thereby modulate sodium absorption. Patch clamp studies were conducted on inside-out patches of the apical membrane of IMCD cells grown in primary culture. Guanosine 5'-triphosphate (GTP) and the nonhydrolyzable GTP analogue, GTP gamma S, which activate G proteins, increased the open probability of the cation channel. In contrast, the nonhydrolyzable GDP analogue, GDP beta S, which decreases G protein activity, inhibited the channel. Pertussis toxin also reduced the open probability of the channel. Addition of the alpha *i-3 subunit of Gi to the solution bathing the cytoplasmic surface of the membrane increased the open probability in a dose-dependent manner (2-200 pM). The threshold concentration for activation by alpha *i-3 was 2 pM. Activation of the cation channel by alpha *i-3 was not mediated via a protein kinase. The IMCD is the first polarized epithelium in which an ion channel has been shown to be directly regulated by a G protein. Thus, G proteins are important elements in regulating sodium absorption by the IMCD.
我们研究了GTP结合蛋白（G蛋白）是否调节肾内髓集合管（IMCD）细胞顶端膜中的钠传导通道，从而调节钠的吸收。对原代培养的IMCD细胞顶端膜的外翻膜片进行膜片钳研究。激活G蛋白的鸟苷5'-三磷酸（GTP）和不可水解的GTP类似物GTPγS增加了阳离子通道的开放概率。相反，降低G蛋白活性的不可水解的GDP类似物GDPβS则抑制了该通道。百日咳毒素也降低了通道的开放概率。将Gi的αi-3亚基添加到浴于膜细胞质表面的溶液中，以剂量依赖方式（2-200 pM）增加了开放概率。αi-3激活的阈值浓度为2 pM。α*i-3对阳离子通道的激活不是通过蛋白激酶介导的。IMCD是首个被证明离子通道受G蛋白直接调节的极化上皮细胞。因此，G蛋白是调节IMCD钠吸收的重要因素。
