Blazer-Yost B L, Cox M, Furlanetto R
Department of Medicine, Veterans Administration Medical Center, Philadelphia, Pennsylvania.
Am J Physiol. 1989 Oct;257(4 Pt 1):C612-20. doi: 10.1152/ajpcell.1989.257.4.C612.
We compared the concentration dependence of insulin- and insulin-like growth factor I (IGF I)-stimulated Na+ transport with ligand-receptor affinities in the urinary bladder of the toad Bufo marinus. Threshold, half-maximal, and maximal natriferic concentrations of both peptides were approximately 0.1, 1, and 10 nM, respectively. Amiloride, but not ethyl isopropyl amiloride, (10(-5) M), abolished Na+ transport. Maximal responses to either peptide rendered the tissue insensitive to challenge with the other. Separate insulin and IGF I receptors were identified by equilibrium binding and polyacrylamide gel electrophoresis of cross-linked ligand-receptor complexes. For both peptides, half-maximal binding occurred at 3-10 nM; crossover binding to the other receptor occurred with 10- and 100-fold lower affinity. Thus, in this model "high-resistance" renal epithelium, 1) ligand binding to specific insulin and IGF I receptors stimulates transcellular Na+ flux, 2) the natriferic effects of insulin and IGF I apparently depend on activation of apical Na+ channels rather than Na+-H+ antiporters, and 3) the natriferic pathways activated by insulin and IGF I appear to converge subsequent to ligand-receptor binding but before the final transport ("effector") step(s).
我们比较了胰岛素和胰岛素样生长因子I（IGF I）刺激的蟾蜍海蟾蜍膀胱中Na⁺转运的浓度依赖性与配体-受体亲和力。两种肽的阈值、半数最大和最大促钠排泄浓度分别约为0.1、1和10 nM。氨氯地平（10⁻⁵ M）而非乙基异丙基氨氯地平可消除Na⁺转运。对任一肽的最大反应使组织对另一种肽的刺激不敏感。通过交联配体-受体复合物的平衡结合和聚丙烯酰胺凝胶电泳鉴定了单独的胰岛素和IGF I受体。对于两种肽，半数最大结合发生在3 - 10 nM；与另一种受体的交叉结合亲和力低10倍和100倍。因此，在这个模型的“高阻力”肾上皮中，1）配体与特定的胰岛素和IGF I受体结合刺激跨细胞Na⁺通量，2）胰岛素和IGF I的促钠排泄作用显然取决于顶端Na⁺通道的激活而非Na⁺-H⁺反向转运体，3）胰岛素和IGF I激活的促钠排泄途径似乎在配体-受体结合之后但在最终转运（“效应器”）步骤之前汇聚。
