人肠基底外侧膜囊泡中的钠转运

Sodium transport in human intestinal basolateral membrane vesicles.

作者信息

Zamir Z, Barry J A, Ramaswamy K

机构信息

Department of Medicine, Zablocki Veterans Administration Medical Center, Milwaukee, Wisconsin.

出版信息

Gastroenterology. 1992 Dec;103(6):1817-22. doi: 10.1016/0016-5085(92)91440-f.

DOI:10.1016/0016-5085(92)91440-f

PMID:1333427

Abstract

The current investigation was aimed at characterizing transport pathways for Na+ in basolateral membrane vesicles (BLMV) isolated from organ donor jejunum and ileum. An outward proton gradient [pH inside, 5.5; pH outside, 7.5] led to a 4-5-fold stimulation of transport rates compared with the absence of proton-gradient conditions in both human jejunal and ileal BLMV. Voltage-clamping the vesicles (K+ inside = K+ outside + valinomycin) reduced the uptake of 22Na by 20%, indicating a minor conductive component of Na+ transport. Uptake of 22Na (1 mmol/L) in voltage-clamped BLMV was inhibited 70% by 2 mmol/L amiloride. Li+ and NH4+ inhibited transport of 22Na into voltage-clamped BLMV. Transport of Na+ exhibited saturation kinetics, and the Michaelis constant (Km) and Vmax values for jejunum and ileum were similar [Km, 27 +/- 3 mmol/L (jejunum) and 18 +/- 2 mmol/L (ileum); Vmax, 19 +/- 2 nmol.mg protein-1.min-1 (jejunum) and 16 +/- 1 nmol.mg protein-1.min-1 (ileum)]. Vmax values were < 15% of those reported for brush border membrane, whereas Km values were comparable. The results show that Na+ transport in human jejunal and ileal BLMV occurs via an Na+/H+ exchanger and a minor conductive pathway.

摘要

当前的研究旨在表征从器官捐献者的空肠和回肠分离出的基底外侧膜囊泡（BLMV）中Na⁺的转运途径。与在人空肠和回肠BLMV中不存在质子梯度条件相比，向外的质子梯度[内部pH值为5.5；外部pH值为7.5]导致转运速率提高了4至5倍。对囊泡进行电压钳制（内部K⁺ = 外部K⁺ + 缬氨霉素）使²²Na的摄取减少了20%，表明Na⁺转运存在少量的传导成分。在电压钳制的BLMV中，²²Na（1 mmol/L）的摄取被2 mmol/L的氨氯吡咪抑制了70%。Li⁺和NH₄⁺抑制²²Na向电压钳制的BLMV中的转运。Na⁺的转运表现出饱和动力学，空肠和回肠的米氏常数（Km）和最大反应速率（Vmax）值相似[Km，27 ± 3 mmol/L（空肠）和18 ± 2 mmol/L（回肠）；Vmax，19 ± 2 nmol·mg蛋白⁻¹·min⁻¹（空肠）和16 ± 1 nmol·mg蛋白⁻¹·min⁻¹（回肠）]。Vmax值小于报道的刷状缘膜的Vmax值的15%，而Km值相当。结果表明，人空肠和回肠BLMV中的Na⁺转运通过Na⁺/H⁺交换器和一条少量的传导途径进行。