Doble M A, Tola V B, Cima R R, Zinner M J, Klein M A, Soybel D I
Department of Surgery, Brigham and Women's Hospital, Boston, MA, USA.
J Gastrointest Surg. 2000 Sep-Oct;4(5):531-5. doi: 10.1016/s1091-255x(00)80097-9.
Water-coupled Na&sup+ absorption in the colon is mediated principally by Na+/H+ exchange (isoforms NHE2 and NHE3). To determine whether luminal ion composition or osmolarity influences NHE expression in colon mucosa, two groups (n = 6 in each) of adult male Sprague-Dawley rats underwent sham laparotomy or loop ileostomy. In these studies, diversion did not markedly alter mRNA levels for NHE2, NHE3, or Na+/K+, at 8 or 21 days, indicating that loss of luminal volume does not alter NHE gene expression. To evaluate the effects of specific luminal components, we infused equal volumes of half-normal (154 mOsm) or iso-osmolar (308 mOsm) solutions of saline and mannitol into the diverted colon. All solutions elicited significant (45% to 60%; P <0.05) decreases in mRNA levels for NHE3, with iso-osmolar mannitol eliciting the greatest changes. Decreases in NHE2 and Na+/K+ mRNA levels were observed following these infusions but were not as marked as the changes for NHE3. These findings suggest that (1) loss of luminal Na+ is not, in itself, a signal that regulates NHE expression and (2) infusion of any solute, including Na+ itself, provides a signal to downregulate expression of NHE3 in colon mucosa.
结肠中与水偶联的钠离子吸收主要由钠/氢交换体（同工型NHE2和NHE3）介导。为了确定肠腔离子组成或渗透压是否影响结肠黏膜中NHE的表达，两组成年雄性Sprague-Dawley大鼠（每组n = 6）分别接受假剖腹手术或回肠造口术。在这些研究中，在第8天或第21天，肠腔改道并未显著改变NHE2、NHE3或钠/钾离子的mRNA水平，这表明肠腔容量的减少不会改变NHE基因的表达。为了评估特定肠腔成分的影响，我们向改道的结肠中注入等体积的半正常（154 mOsm）或等渗（308 mOsm）的生理盐水和甘露醇溶液。所有溶液均引起NHE3的mRNA水平显著下降（45%至60%；P <0.05），等渗甘露醇引起的变化最大。在这些注入后观察到NHE2和钠/钾离子mRNA水平下降，但不如NHE3的变化明显。这些发现表明：（1）肠腔钠离子的丢失本身并不是调节NHE表达的信号；（2）注入任何溶质，包括钠离子本身，都会提供一个信号来下调结肠黏膜中NHE3的表达。
