Greig E R, Mathialahan T, Boot-Handford R P, Sandle G I
Department of Medicine, University of Manchester, Hope Hospital, Salford, Manchester, UK.
Gut. 2003 Nov;52(11):1607-15. doi: 10.1136/gut.52.11.1607.
Human distal nephron and distal colon both exhibit mineralocorticoid sensitive electrogenic Na(+) absorption and make significant contributions to Na(+) homeostasis. Na(+) resorption in the distal nephron diminishes with age but it is unclear whether a similar change occurs in the distal colon.
To evaluate the effect of age on expression of apical Na(+) channels and basolateral Na(+), K(+)-ATPase, and on the responsiveness of electrogenic Na(+) absorption to mineralocorticoid stimulation in human distal colon and rectum.
Mucosal biopsies were obtained from healthy sigmoid colon and proximal rectum in "young" (aged 20-40 years) and "old" (aged 70 years or over) patients during routine colonoscopy/flexible sigmoidoscopy. Na(+) channel subunits and Na(+), K(+)-ATPase isoforms were studied at the mRNA level by in situ hybridisation and northern blotting, and at the protein level by immunocytochemistry and western blotting. The mineralocorticoid responsiveness of electrogenic Na(+) absorption was evaluated in the two groups by measuring amiloride sensitive electrical potential difference (PD) in the proximal rectum before and 24 hours after oral administration of 1 mg of fludrocortisone.
Na(+) channel subunit and Na(+), K(+)-ATPase isoform expression at the level of mRNA and protein was similar in "young" and "old" patients. Both basal and the fludrocortisone stimulated amiloride sensitive rectal PDs were similar in the two groups.
In contrast with the distal nephron, mineralocorticoid sensitive electrogenic Na(+) absorption in the human distal colon does not diminish with age, and may be particularly important in maintaining Na(+) homeostasis in the elderly.
人类远端肾单位和远端结肠均表现出盐皮质激素敏感性电中性钠（Na⁺）吸收，对钠平衡有重要贡献。远端肾单位中的钠重吸收随年龄增长而减少，但尚不清楚远端结肠是否会发生类似变化。
评估年龄对人类远端结肠和直肠顶端钠通道及基底外侧钠钾ATP酶表达的影响，以及对电中性钠吸收对盐皮质激素刺激反应性的影响。
在常规结肠镜检查/乙状结肠镜检查期间，从“年轻”（20 - 40岁）和“老年”（70岁及以上）患者的健康乙状结肠和直肠近端获取黏膜活检组织。通过原位杂交和Northern印迹法在mRNA水平研究钠通道亚基和钠钾ATP酶同工型，通过免疫细胞化学和Western印迹法在蛋白质水平进行研究。通过测量口服1 mg氟氢可的松前及24小时后直肠近端的氨氯地平敏感电位差（PD），评估两组中电中性钠吸收对盐皮质激素的反应性。
“年轻”和“老年”患者在mRNA和蛋白质水平的钠通道亚基及钠钾ATP酶同工型表达相似。两组的基础及氟氢可的松刺激后的氨氯地平敏感直肠PD相似。
与远端肾单位不同，人类远端结肠中盐皮质激素敏感性电中性钠吸收不会随年龄增长而减少，在维持老年人钠平衡方面可能尤为重要。
