Watanabe S, Matsushita K, Stokes J B, McCray P B
Department of Internal Medicine, University of Iowa College of Medicine and Veterans Affairs Medical Center, Iowa City, Iowa 52242, USA.
Am J Physiol. 1998 Dec;275(6):G1227-35. doi: 10.1152/ajpgi.1998.275.6.G1227.
Na+ absorption via amiloride-sensitive Na+ channels is of critical importance in the transition between fetal and neonatal life in several tissues, including the colon, lung, and kidney. To characterize and contrast the mRNA expression of each of the three epithelial Na+ channel complex (ENaC) subunits, we conducted RNase protection assays (RPA) and in situ hybridization in colon and lung in fetal (17, 19, 20, and 21 days) and postnatal (1, 3, 9, 15, and 30 days) rats (r). In the colon the alpha-, beta-, and gamma-rENaC subunits showed quantitatively different but qualitatively similar expression. All three subunits gradually increased in abundance from fetal day 19 through day 30 of life. The amount of each subunit on day 30 was approximately three times the amount at day 1. In situ hybridization showed that each subunit was localized to the surface epithelial cells with minimal expression in the crypts. The lung showed a completely different pattern. In contrast to the colon, the total amount of alpha-rENaC mRNA (by RPA) in the lung increased dramatically from fetal day 19 to 21, whereas beta- and gamma-rENaC showed modest prenatal increases. The amounts of all three mRNAs fell after birth through day 9 (to about 75% of the day 1 value). On days 15 and 30 the amount of mRNA rose to approach the values on day 1. alpha-rENaC mRNA abundance always exceeded beta- and gamma-rENaC, and the quantitative expression was different for alpha- than for beta- and gamma-rENaC. In situ hybridization studies showed that all three subunits were expressed in epithelial cells of the bronchi, bronchioles, and alveoli and not in blood vessels. These studies show striking developmental heterogeneity in rENaC mRNA expression between lung and colon, probably reflecting different developmental regulatory mechanisms in these organs.
通过阿米洛利敏感的钠离子通道进行的钠离子吸收，在包括结肠、肺和肾脏在内的多种组织从胎儿期到新生儿期的转变过程中至关重要。为了表征和对比三种上皮钠离子通道复合物（ENaC）亚基各自的mRNA表达情况，我们在胎儿期（17、19、20和21天）及出生后（1、3、9、15和30天）的大鼠结肠和肺中进行了核糖核酸酶保护分析（RPA）和原位杂交。在结肠中，α-、β-和γ-rENaC亚基显示出数量上不同但质量上相似的表达。从胎儿期第19天到出生后第30天，所有三个亚基的丰度都逐渐增加。出生后第30天每个亚基的量约为第1天的三倍。原位杂交显示每个亚基定位于表面上皮细胞，隐窝中的表达极少。肺呈现出完全不同的模式。与结肠相反，肺中α-rENaC mRNA的总量（通过RPA测定）从胎儿期第19天到21天急剧增加，而β-和γ-rENaC在产前有适度增加。出生后到第9天，所有三种mRNA的量都下降（降至第1天值的约75%）。在第15天和30天，mRNA的量上升至接近第1天的值。α-rENaC mRNA的丰度总是超过β-和γ-rENaC，并且α-rENaC与β-和γ-rENaC的定量表达不同。原位杂交研究表明，所有三个亚基均在支气管、细支气管和肺泡的上皮细胞中表达，而不在血管中表达。这些研究表明，大鼠肺和结肠中rENaC mRNA表达存在显著的发育异质性，这可能反映了这些器官中不同的发育调节机制。
