Seshadri Ramanathan M, Klein Janet D, Smith Tekla, Sands Jeff M, Handlogten Mary E, Verlander Jill W, Weiner I David
Division of Nephrology, Hypertension, and Transplantation, Univ. of Florida College of Medicine, Gainesville, FL, USA.
Am J Physiol Renal Physiol. 2006 Jun;290(6):F1443-52. doi: 10.1152/ajprenal.00459.2005. Epub 2006 Jan 24.
The primary mechanism by which the kidneys mediate net acid excretion is through ammonia metabolism. In the current study, we examined whether chronic metabolic acidosis, which increases ammonia metabolism, alters the cell-specific and/or the subcellular expression of the ammonia transporter family member, Rhcg, in the outer medullary collecting duct in the inner stripe (OMCDi). Chronic metabolic acidosis was induced in normal SD rats by HCl ingestion for 7 days; controls were pair-fed. The subcellular distribution of Rhcg was determined using immunogold electron microscopy and morphometric analyses. In intercalated cells, acidosis increased total Rhcg, apical plasma membrane Rhcg, and the proportion of total cellular Rhcg in the apical plasma membrane. Intracellular Rhcg decreased significantly, and basolateral Rhcg was unchanged. Because apical plasma membrane length increased in parallel with apical Rhcg immunolabel, apical plasma membrane Rhcg density was unchanged. In principal cells, acidosis increased total Rhcg, apical plasma membrane Rhcg, and the proportion of total cellular Rhcg in the apical plasma membrane while decreasing the intracellular proportion. In contrast to the intercalated cell, chronic metabolic acidosis did not significantly alter apical boundary length; accordingly, apical plasma membrane Rhcg density increased. In addition, basolateral Rhcg immunolabel increased in response to chronic metabolic acidosis. These results indicate that in the rat OMCDi 1) chronic metabolic acidosis increases apical plasma membrane Rhcg in both the intercalated cell and principal cell where it may contribute to enhanced apical ammonia secretion; 2) increased apical plasma membrane Rhcg results from both increased total protein and changes in the subcellular distribution of Rhcg; 3) the mechanism of Rhcg subcellular redistribution differs in intercalated and principal cells; and 4) Rhcg may contribute to regulated basolateral ammonia transport in the principal cell.
肾脏调节净酸排泄的主要机制是通过氨代谢。在本研究中，我们检测了增加氨代谢的慢性代谢性酸中毒是否会改变内髓质内带外髓集合管（OMCDi）中氨转运体家族成员Rhcg的细胞特异性和/或亚细胞表达。通过给正常SD大鼠灌胃HCl 7天诱导慢性代谢性酸中毒；对照组采用配对喂食。使用免疫金电子显微镜和形态计量分析确定Rhcg的亚细胞分布。在闰细胞中，酸中毒增加了Rhcg总量、顶端质膜Rhcg以及顶端质膜中总细胞Rhcg的比例。细胞内Rhcg显著减少，基底外侧Rhcg不变。由于顶端质膜长度与顶端Rhcg免疫标记平行增加，顶端质膜Rhcg密度不变。在主细胞中，酸中毒增加了Rhcg总量、顶端质膜Rhcg以及顶端质膜中总细胞Rhcg的比例，同时降低了细胞内比例。与闰细胞不同，慢性代谢性酸中毒并未显著改变顶端边界长度；因此，顶端质膜Rhcg密度增加。此外，基底外侧Rhcg免疫标记因慢性代谢性酸中毒而增加。这些结果表明，在大鼠OMCDi中：1）慢性代谢性酸中毒增加了闰细胞和主细胞顶端质膜Rhcg，这可能有助于增强顶端氨分泌；2）顶端质膜Rhcg增加是由于总蛋白增加和Rhcg亚细胞分布变化；3）Rhcg亚细胞重新分布的机制在闰细胞和主细胞中不同；4）Rhcg可能有助于主细胞中基底外侧氨转运的调节。
