Vázquez C M, Coleto R, Zanetti R, Ruiz-Gutierrez V
Departamento de Fisiologia y Biologia Animal, Facultad de Farmacia, Univ., Sevilla, Spain.
Cell Mol Life Sci. 1997 May;53(5):442-6. doi: 10.1007/s000180050053.
In the present study, we have examined the intestinal Na+ transport, through the Na+)-H+ exchanger in ileal brush-border membrane vesicles (BBMV) isolated from spontaneously hypertensive rats (SHR), and normotensive Wistar Kyoto (WKY) rats as a control group. Na+ uptake into ileal BBMV was stimulated the presence of a proton gradient (pH 5.5 inside/pH 7.5 outside) in SHR and WKY rats, resulting in a transient accumulation (overshoot) in both groups of rats. No overshoot was observed in the absence of a pH gradient. The magnitude of the accumulation was significantly higher in SHR than in WKY rats. Uptake of Na+ at equilibrium was identical in the presence and the absence of a proton gradient and was not changed in SHR. The use of amiloride inhibited pH gradient-driven Na+ uptake in a dose-dependent manner with a Ki of 90 microM and 100 microM for SHR and WKY rats, respectively. The relationship between proton gradient-driven Na+ uptake and external Na+ concentration was saturable and conformed to Michaelis-Menten kinetics in both SHR and WKY rats. Lineweaver-Burk analysis of the pH gradient-driven Na+ uptake indicated values of Vmax that were significantly increased in SHR compared to WKY rats (11.4 +/- 0.55 nmol/mg/8 s vs. 4.96 +/- 0.78 nmol/mg/8 s for SHR and WKY rats, respectively). In contrast, similar K(m) for Na+ were found between SHR and WKY rats (4.0 +/- 0.2 mM vs. 4.9 +/- 0.6 mM for SHR and WKY rats, respectively). These studies show derangement in ileal BBMV Na+ transport of SHR, which is characterized by increased Na(+)-H+ exchanger activity.
在本研究中，我们检测了从自发性高血压大鼠（SHR）分离的回肠刷状缘膜囊泡（BBMV）中通过Na⁺-H⁺交换体的肠道Na⁺转运，并以血压正常的Wistar Kyoto（WKY）大鼠作为对照组。在SHR和WKY大鼠中，质子梯度（内部pH 5.5/外部pH 7.5）的存在刺激了Na⁺进入回肠BBMV，导致两组大鼠均出现短暂积累（过冲）。在没有pH梯度的情况下未观察到过冲现象。SHR中积累的幅度显著高于WKY大鼠。在有和没有质子梯度的情况下，平衡时Na⁺的摄取是相同的，且在SHR中没有变化。氨氯吡咪的使用以剂量依赖性方式抑制了pH梯度驱动的Na⁺摄取，SHR和WKY大鼠的抑制常数（Ki）分别为90 μM和100 μM。在SHR和WKY大鼠中，质子梯度驱动的Na⁺摄取与外部Na⁺浓度之间的关系是饱和的，符合米氏动力学。对pH梯度驱动的Na⁺摄取进行Lineweaver-Burk分析表明，与WKY大鼠相比，SHR的最大反应速度（Vmax）值显著增加（SHR和WKY大鼠分别为11.4±0.55 nmol/mg/8 s和4.96±0.78 nmol/mg/8 s）。相反，SHR和WKY大鼠之间的Na⁺米氏常数（K(m)）相似（SHR和WKY大鼠分别为4.0±0.2 mM和4.9±0.6 mM）。这些研究表明SHR的回肠BBMV Na⁺转运紊乱，其特征是Na⁺-H⁺交换体活性增加。
