Ishikawa S, Okada K, Saito T
Department of Medicine, Jichi Medical School, Tochigi, Japan.
Endocrinology. 1992 Jan;130(1):17-22. doi: 10.1210/endo.130.1.1309326.
The present study was undertaken to determine whether the change in cellular Na+ concentration ( [Na+]i) or cellular pH (pHi) is essential for the modulation by Na+/H+ antiporter of the cellular action of arginine vasopressin (AVP) in renal inner medullary collecting duct cells in culture. Extracellular Na+ depletion promptly decreased [Na+]i from 15.8 to 5.4 mM (P less than 0.01), which was closely related to the decrease in pHi (7.19 to 6.97; P less than 0.01). In the presence of 0.5 mM 3-isobutyl-1-methylxanthine, AVP increased cellular cAMP production in a dose-dependent manner. This was significantly blunted in the Na(+)-depleted cells (1 nM AVP; 481.9 vs. 341.0 fmol/micrograms protein; P less than 0.01). When cells were incubated with the Na(+)-depleted medium containing 25 mM NaHCO3, [Na+]i decreased promptly, but the pHi remained unchanged. Under this condition, the AVP-induced increase in cellular cAMP production was not altered (1 nM AVP; 390.9 vs. 334.8 fmol/micrograms protein). Also, after the Na(+)-depleted cells were incubated in 20 mM NH4Cl, which promptly normalized pHi despite the decreased [Na+]i, the response of cAMP production to AVP was restored. Amiloride (1 x 10(-5)-1 x 10(-3) M), which blocks the Na+/H+ exchange, decreased pHi and AVP- and forskolin-induced cAMP production in a dose-dependent manner. These results indicate that the decrease in [Na+]i promptly inhibits AVP-induced cAMP production mediated through the reduction in pHi in renal inner medullary collecting duct cells.
本研究旨在确定细胞内钠离子浓度（[Na⁺]i）或细胞内pH值（pHi）的变化对于培养的肾内髓集合管细胞中Na⁺/H⁺反向转运体调节精氨酸加压素（AVP）细胞作用是否至关重要。细胞外钠离子耗竭迅速使[Na⁺]i从15.8 mM降至5.4 mM（P<0.01），这与pHi的降低密切相关（从7.19降至6.97；P<0.01）。在存在0.5 mM 3-异丁基-1-甲基黄嘌呤的情况下，AVP以剂量依赖方式增加细胞内cAMP生成。在钠离子耗竭的细胞中这种作用明显减弱（1 nM AVP；481.9对341.0 fmol/μg蛋白质；P<0.01）。当细胞与含25 mM NaHCO₃的钠离子耗竭培养基孵育时，[Na⁺]i迅速降低，但pHi保持不变。在此条件下，AVP诱导的细胞内cAMP生成未改变（1 nM AVP；390.9对334.8 fmol/μg蛋白质）。此外，在钠离子耗竭的细胞在20 mM NH₄Cl中孵育后，尽管[Na⁺]i降低但pHi迅速恢复正常，cAMP生成对AVP的反应也恢复。氨氯地平（1×10⁻⁵ - 1×10⁻³ M）可阻断Na⁺/H⁺交换，以剂量依赖方式降低pHi以及AVP和福斯可林诱导的cAMP生成。这些结果表明，[Na⁺]i的降低通过肾内髓集合管细胞中pHi的降低迅速抑制AVP诱导的cAMP生成。
