McSwine R L, Musch M W, Bookstein C, Xie Y, Rao M, Chang E B
Section of Gastroenterology, Department of Medicine, University of Chicago, Chicago, Illinois 60637, USA.
Am J Physiol. 1998 Sep;275(3):C693-701. doi: 10.1152/ajpcell.1998.275.3.C693.
We examined the regulation of the Na+/H+ exchangers (NHEs) NHE2 and NHE3 by expressing them in human intestinal C2/bbe cells, which spontaneously differentiate and have little basal apical NHE activity. Unidirectional apical membrane 22Na+ influxes were measured in NHE2-transfected (C2N2) and NHE3-transfected (C2N3) cells under basal and stimulated conditions, and their activities were distinguished as the HOE-642-sensitive and -insensitive components of 5-(N,N-dimethyl)amiloride-inhibitable flux. Both C2N2 and C2N3 cells exhibited increased apical membrane NHE activity under non-acid-loaded conditions compared with nontransfected control cells. NHE2 was inhibited by 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate and thapsigargin, was stimulated by serum, and was unaffected by cGMP- and protein kinase C-dependent pathways. In contrast, NHE3 was inhibited by all regulatory pathways examined. Under acid-loaded conditions (which increase apical Na+ influx), NHE2 and NHE3 exhibited similar patterns of regulation, suggesting that the second messenger effects observed were not secondary to effects on cell pH. Thus, in contrast to their expression in nonepithelial cells, NHE2 and NHE3 expressed in an epithelial cell line behave similarly to endogenously expressed intestinal apical membrane NHEs. We conclude that physiological regulation and function of epithelium-specific NHEs are dependent on tissue-specific factors and/or conditional requirements.
我们通过在人肠道C2/bbe细胞中表达Na⁺/H⁺交换体（NHEs）NHE2和NHE3来研究其调控机制，该细胞可自发分化且基础顶膜NHE活性较低。在基础和刺激条件下，测量NHE2转染细胞（C2N2）和NHE3转染细胞（C2N3）的单向顶膜²²Na⁺内流，并将其活性区分为5 -（N，N -二甲基）氨氯吡脒抑制通量的HOE - 642敏感和不敏感成分。与未转染的对照细胞相比，C2N2和C2N3细胞在非酸负荷条件下均表现出顶膜NHE活性增加。NHE2受8 -（4 -氯苯硫基）腺苷3'，5'-环磷酸酯和毒胡萝卜素抑制，受血清刺激，不受cGMP和蛋白激酶C依赖性途径影响。相比之下，NHE3受所有检测的调节途径抑制。在酸负荷条件下（增加顶膜Na⁺内流），NHE2和NHE3表现出相似的调节模式，表明观察到的第二信使效应并非继发于对细胞pH的影响。因此，与它们在非上皮细胞中的表达不同，在上皮细胞系中表达的NHE2和NHE3的行为与内源性表达的肠道顶膜NHEs相似。我们得出结论，上皮特异性NHEs的生理调节和功能取决于组织特异性因素和/或条件需求。
