Laboratory of Animal Physiology and Biochemistry, Nanjing Agricultural University, Nanjing 210095, PR China.
J Anim Sci. 2012 Jan;90(1):307-17. doi: 10.2527/jas.2011-3854. Epub 2011 Aug 19.
Rumen epithelial Na(+)/H(+) exchanger (NHE) catalyzes the exchange of extracellular Na(+) for intracellular H(+). Thus, it is of importance in the maintenance of Na and pH homeostasis of rumen epithelial cells. We have tested the hypothesis that an increase in energy and protein intake induces alterations of NHE isoform 1, 2, and 3 (NHE1, NHE1, and NHE3, respectively) mRNA abundance in the rumen epithelium of goats. Goats (n = 26) were randomly allocated to 2 experiments (n = 16 in Exp. 1, and n = 10 in Exp. 2) and fed either peanut straw ad libitum [PNS, n = 8 in Exp. 1, and n = 5 in Exp. 2; 600 kJ of ME/(kg(0.75)·d)] or PNS + concentrate [CF, n = 8 in Exp. 1, and n = 5 in Exp. 2; 1,000 kJ of ME/(kg(0.75)·d)] for 42 d. Concentrate (400 g/d) was given daily (0800 to 1700 h) in 4 equal portions at 3-h intervals. In Exp. 1, the goats were euthanized 2 h after the last portion of concentrate was fed, and in Exp. 2, the goats were euthanized after a fasting period of 16 h. In Exp. 1, goats in the CF treatment exhibited a greater ruminal short-chain fatty acid (SCFA) concentration (140.6 ± 1.30 mM) compared with those in the PNS treatment (114.3 ± 3.11 mM; P < 0.001), and pH decreased from 6.9 ± 0.09 to 5.9 ± 0.04 (P < 0.001). Correspondingly, the mRNA expression of NHE1 and NHE3 in the rumen epithelium was greater by 20% (P = 0.041) and 25% (P = 0.043) for goats in the CF treatment than for those in the PNS treatment. However, in Exp. 2, 16 h of fasting abolished differences in ruminal SCFA concentration, pH, and NHE mRNA expression between goats in the CF and PNS treatments. In both Exp. 1 and 2, a positive correlation was observed between ruminal SCFA concentration and expression of mRNA in NHE1 and NHE3, whereas expression was negatively correlated with ruminal pH. In in vitro studies with isolated rumen epithelial cells from goats fed dried grass, exposure to pH of 6.8 or to 20 mM SCFA increased (P < 0.01) NHE1 and NHE3 mRNA expression, as compared with exposure to pH of 7.4 or the absence of SCFA. A combination of reduced pH (6.8) and SCFA (20 mM) further enhanced (P < 0.05) NHE1 and NHE3 mRNA expression, indicating synergism between an increased concentration of SCFA and low pH (P < 0.05). Messenger RNA expression of NHE2 did not vary in vitro with pH (6.8) or SCFA (20 mM) or in vivo in Exp. 1 and 2. Thus, diet-dependent rumen epithelial NHE1 and NHE3 expression is probably related to ruminal SCFA concentration and pH, but that is not the case with NHE2.
瘤胃上皮钠（+）/氢（+）交换器（NHE）催化细胞外 Na+与细胞内 H+的交换。因此，它对于维持瘤胃上皮细胞的 Na+和 pH 平衡非常重要。我们已经测试了这样一个假设，即增加能量和蛋白质的摄入会导致山羊瘤胃上皮细胞中 NHE 同工型 1、2 和 3（NHE1、NHE1 和 NHE3，分别）mRNA 丰度的改变。将 26 只山羊（n = 26）随机分配到 2 个实验中（实验 1 中 n = 16，实验 2 中 n = 10），并分别自由采食花生秸秆（PNS，n = 8，实验 1；n = 5，实验 2；600 kJ ME/（kg（0.75）·d））或 PNS + 浓缩饲料（CF，n = 8，实验 1；n = 5，实验 2；1000 kJ ME/（kg（0.75）·d））42 d。浓缩饲料（400 g/d）每天（0800 至 1700 h）分 4 次等份给予，间隔 3 h。在实验 1 中，在最后一次给予浓缩饲料后 2 h 对山羊进行安乐死，在实验 2 中，在禁食 16 h 后对山羊进行安乐死。在实验 1 中，与 PNS 处理的山羊相比，CF 处理的山羊瘤胃短链脂肪酸（SCFA）浓度更高（140.6 ± 1.30 mM），114.3 ± 3.11 mM；P < 0.001），pH 值从 6.9 ± 0.09 下降到 5.9 ± 0.04（P < 0.001）。相应地，与 PNS 处理的山羊相比，CF 处理的山羊瘤胃上皮 NHE1 和 NHE3 的 mRNA 表达分别增加了 20%（P = 0.041）和 25%（P = 0.043）。然而，在实验 2 中，16 h 的禁食消除了 CF 和 PNS 处理的山羊瘤胃 SCFA 浓度、pH 值和 NHE mRNA 表达之间的差异。在实验 1 和 2 中，瘤胃 SCFA 浓度与 NHE1 和 NHE3 的 mRNA 表达呈正相关，而表达与瘤胃 pH 值呈负相关。在体外研究中，用山羊分离的瘤胃上皮细胞进行研究，暴露于 pH 6.8 或 20 mM SCFA 会增加 NHE1 和 NHE3 的 mRNA 表达（P < 0.01），而与暴露于 pH 7.4 或不存在 SCFA 相比。pH 值降低（6.8）和 SCFA（20 mM）的组合进一步增强（P < 0.05）NHE1 和 NHE3 的 mRNA 表达，表明 SCFA 浓度增加和低 pH 值之间存在协同作用（P < 0.05）。在实验 1 和 2 中，体外 pH 值（6.8）或 SCFA（20 mM）或体内 NHE2 的信使 RNA 表达没有变化。因此，瘤胃上皮细胞 NHE1 和 NHE3 的表达可能与瘤胃 SCFA 浓度和 pH 值有关，但与 NHE2 无关。
