Takahashi N, Ito O, Abe K
Second Department of Internal Medicine, Tohoku University School of Medicine, Aoba-ku, Sendai, Japan.
Hypertens Res. 1996 Jun;19 Suppl 1:S41-5. doi: 10.1291/hypres.19.supplementi_s41.
The direct effect of insulin on NaCl transport in proximal tubules and thick ascending limbs of Henle's loop were examined. First, the effects of insulin on intracellular pH (pHi) in the in vitro microperfused rabbit S2 proximal straight tubules (PST) were examined using a fluorescent technique. Addition of insulin to the bath increased pHi in a dose-dependent manner at concentrations ranging from 10(-11) to 10(-6) mol/l, and its ED50 was 10(-9) mol/l. The insulin-induced pHi increase was almost completely inhibited by 10(-3) mol/l amiloride in the lumen, indicating that insulin activates luminal Na/H exchange in PST. Next, the effect of insulin on the transepithelial voltage (Vt) and lumen-to-bath Cl flux (JCl) were examined in the in vitro microperfused rabbit medullary thick ascending limbs of Henle's loop (MTAL). Insulin in the bath increased Vt in a dose-dependent manner, and its ED50 was 5 X 10(-9) mol/l. Insulin significantly increased JCl. The insulin-mediated increase in Vt was abolished by ouabain and furosemide. Dibutyryl-cAMP (dbcAMP) increased Vt and JCl. H-8 abolished the effect of dbcAMP, while it did not inhibit the actions of insulin. Removal of extracellular Ca did not affect the effects of insulin on Vt and JCl. Chelation of intracellular Ca with BAPTA/AM inhibited the actions of insulin without affecting basal values. Calmodulin (CaM) inhibitors, trifluoperazine and W-7, inhibited the actions of insulin more than 90%. These results indicate that insulin directly increases NaCl reabsorption in the MTAL, which requires the activation of Ca-CaM system, independent of the adenylate cyclase-cAMP-PKA system. In conclusion, insulin directly stimulates NaCl reabsorption in the in vitro microperfused rabbit PST and MTAL.
研究了胰岛素对近端小管和髓袢升支粗段中氯化钠转运的直接作用。首先，使用荧光技术检测了胰岛素对体外微灌注兔S2近端直小管（PST）细胞内pH（pHi）的影响。在浴液中添加胰岛素，在浓度范围为10^(-11)至10^(-6)mol/L时，以剂量依赖方式升高pHi，其半数有效浓度（ED50）为10^(-9)mol/L。管腔内10^(-3)mol/L的氨氯吡咪几乎完全抑制了胰岛素诱导的pHi升高，表明胰岛素激活了PST中的管腔钠/氢交换。接下来，在体外微灌注兔髓袢升支粗段（MTAL）中检测了胰岛素对跨上皮电压（Vt）和管腔至浴液氯通量（JCl）的影响。浴液中的胰岛素以剂量依赖方式升高Vt，其ED50为5×10^(-9)mol/L。胰岛素显著增加JCl。哇巴因和呋塞米消除了胰岛素介导的Vt升高。二丁酰环磷腺苷（dbcAMP）升高Vt和JCl。H-8消除了dbcAMP的作用，而它不抑制胰岛素的作用。去除细胞外钙不影响胰岛素对Vt和JCl的作用。用BAPTA/AM螯合细胞内钙抑制了胰岛素的作用，而不影响基础值。钙调蛋白（CaM）抑制剂三氟拉嗪和W-7抑制胰岛素作用超过90%。这些结果表明，胰岛素直接增加MTAL中的氯化钠重吸收，这需要激活钙-钙调蛋白系统，独立于腺苷酸环化酶-cAMP-蛋白激酶A系统。总之，胰岛素直接刺激体外微灌注兔PST和MTAL中的氯化钠重吸收。
