Expression of Na channel after total colectomy in remnant ileal epithelium.

背景和目标：众所周知，在直肠结肠切除术患者中，残余小肠中的上皮转运功能可以响应于粪便电解质和液体损失的增加而被调节。本研究采用大鼠结肠切除模型，探讨了肠反应的钠钾转运机制。方法：采用Spregue-Dawley大鼠行直肠切除回肠肛管吻合术。在离体肠段上测量短路电流和~（22）Na通量。通过Northern印迹分析确定肠上皮Na通道的mRNA表达。结果如下：阿米洛利（100 μ mol/L，mocosal side）和阿米洛利类似物苯扎米尔（10 μ mol/L，mocosal side）可降低直肠结肠切除大鼠末端回肠的短路电流和22 Na吸收，但对对照组大鼠无影响。直肠结肠切除术后2 ~ 4周，阿米诺敏感性短路电流的活动扩展到更近端的部分（仍在回肠内）。在此期间，血浆醛固酮水平显著升高，升高的粪便钠浓度显著降低。对照组下段小肠上皮钠通道α、β和γ亚单位mRNA表达较低，而直肠结肠切除组显著升高。结肠切除大鼠回肠的短路电流被四乙基铵（2 mmol/L，粘膜侧）抑制，但同时也被激活，且与阿米洛利敏感性短路电流密切相关。结论：产电钠吸收和可能也四乙基铵敏感的产电钾分泌诱导下段小肠直肠结肠切除术后。这些诱导是由所有三种类型的亚基，α-，β-和γ-rENaC mRNA在转录水平上的增加引起的。这些过程可能有助于从增加的粪便Na损失中恢复。

Background & Aims : It has been known that in patients with proctocolectomy, epithelial transport functions in the remnant small intestine can be regulated in response to the increased fecal electrolyte and fluid loss. By using rat colectomy model, we investigated the Na and K transport mechanisms underlying the intestinal response. Methods : Proctolectomy with ileo-anal anastomosis was performed on Spregue-Dawley rats. Short-circuit current and 22Na fluxes were measured in isolated intestinal segment. Expression of mRNA for epithelial Na channels in the intestine was determined by Northern-blot analysis. Results : Amiloride (100micromol/L,mocosal side) and an amiloride analog benzamil (10micromol/L,mocosal side) reduced short-circuit current and 22Na absorption in the terminal ileum in proctocolectomized rats, but not in control rats. The activities of amirolide-sensitive short-circuit current expanded to a more proximal part (still within the ileum) between 2 and 4 wk after proctocolectomy. Plasma level of aldosterone was markedly elevated and the elevated fecal Na concentration was remarkably reduced during this period. Expression of mRNA for alpha-, beta-and gamma-subunit of epithelial Na channels in the lower small intestine was low in control, but was remarkably elevated in proctocolectomized rats. The short-circuit current, which is inhibited by tetraehyl anmonium (2 mmol/L,mucosal side), was also activated in the ileum of the colectomized rats specially in close association with the amiloride-sensitive short-circuit current. Conclusions : The electrogenic Na absorption and probably also tetraethyl ammonium-sensitive electrogenic K secretions are induced in the lower small intestine after proctocolectomy. These induction is caused by the increase of all three types of subunits, alpha-, beta- andgamma-rENaC mRNA at the transcription level. These processes may contribute to the recovery from the increased fecal Na loss.