Xu Hua, Chen Huacong, Dong Jiali, Lynch Ronald, Ghishan Fayez K
University of Arizona Health Sciences Center, Tucson, AZ, USA.
Cell Physiol Biochem. 2008;21(1-3):109-16. doi: 10.1159/000113752. Epub 2008 Jan 16.
NHE8 is a newly identified NHE isoform expressed in rat intestine. To date, the kinetic characteristics and the intestinal segmental distribution of this NHE isoform have not been studied. This current work was performed to determine the gene expression pattern of the NHE8 transporter along the gastrointestinal tract, as well as its affinity for Na(+), H(+), and sensitivity to known NHE inhibitors HOE694 and S3226. NHE8 was differentially expressed along the GI tract. Higher NHE8 expression was seen in stomach, duodenum, and ascending colon in human, while higher NHE8 expression was seen in jejunum, ileum and colon in adult mouse. Moreover, the expression level of NHE8 is much higher in the stomach and jejunum in young mice compared with adult mice. To evaluate the functional characterictics of NHE8, the pH indicator SNARF-4 was used to monitor the rate of intra-cellular pH (pH(i)) recovery after an NH(4)Cl induced acid load in NHE8 cDNA transfected PS120 cells. The NHE8 cDNA transfected cells exhibited a sodium-dependent proton exchanger activity having a Km for pH(i) of approximately pH 6.5, and a Km for sodium of approximately 23 mM. Low concentration of HOE694 (1 microM) had no effect on NHE8 activity, while high concentration (10 microM) significantly reduced NHE8 activity. In the presence of 80 microM S3226, the NHE8 activity was also inhibited significantly. In conclusion, our work suggests that NHE8 is expressed along the gastrointestinal tract and NHE8 is a functional Na(+)/H(+) exchanger with kinetic characteristics that differ from other apically expressed NHE isoforms.
NHE8是一种新发现的在大鼠肠道中表达的NHE亚型。迄今为止，尚未对该NHE亚型的动力学特征和肠段分布进行研究。开展当前这项工作是为了确定NHE8转运体沿胃肠道的基因表达模式，以及其对Na⁺、H⁺的亲和力和对已知NHE抑制剂HOE694和S3226的敏感性。NHE8在胃肠道中呈差异表达。在人类中，胃、十二指肠和升结肠中可见较高的NHE8表达，而在成年小鼠中，空肠、回肠和结肠中可见较高的NHE8表达。此外，与成年小鼠相比，幼鼠胃和空肠中NHE8的表达水平要高得多。为评估NHE8的功能特性，使用pH指示剂SNARF-4监测NHE8 cDNA转染的PS120细胞在氯化铵诱导的酸负荷后细胞内pH（pH(i)）恢复的速率。NHE8 cDNA转染的细胞表现出钠依赖性质子交换活性，其对pH(i)的Km约为pH 6.5，对钠的Km约为23 mM。低浓度的HOE694（1 μM）对NHE8活性无影响，而高浓度（10 μM）则显著降低NHE8活性。在存在80 μM S3226的情况下，NHE8活性也被显著抑制。总之，我们的研究表明NHE8在胃肠道中表达，并且NHE8是一种功能性的Na⁺/H⁺交换体，其动力学特征不同于其他顶端表达的NHE亚型。
