Hamm L L, Simon E E
Department of Medicine, Washington University, St Louis, MO.
Am J Kidney Dis. 1989 Oct;14(4):253-7. doi: 10.1016/s0272-6386(89)80197-0.
Studies were performed to characterize the determinants of proximal tubule ammonia entry (and retention) in vivo. Rat proximal tubules were studied in vivo using in situ microperfusion. In both normal animals and animals with metabolic acidosis, increasing luminal flow rate significantly enhanced luminal ammonia entry. In contrast, luminal pH was not as important in determining ammonia entry. Analysis of the levels of luminal NH3 in these studies was not consistent with simple diffusion equilibrium of NH3. In animals with chronic metabolic acidosis, additional studies demonstrated that inhibition of the Na+-H+ exchanger had no direct effect on luminal ammonia entry. However, studies of ammonia efflux from tubules perfused with 10 mmol/L ammonia demonstrated significant transport of both NH3 and NH4+. Studies of luminal glutamine deamidation via gamma-glutamyltransferase in control conditions did not indicate a significant role for luminal ammoniagenesis in the superficial proximal tubule in vivo. These and other recent studies of proximal tubule ammonia transport significantly modify the traditional diffusion equilibrium (of NH3) model of ammonia transport. Luminal flow rate is an important determinant of luminal ammonia entry. Transport of NH4+, both into and out of the tubule lumen, represents a major component of total ammonia transport.
开展了多项研究以表征体内近端小管氨进入（及潴留）的决定因素。采用原位微灌注法对大鼠近端小管进行体内研究。在正常动物和患有代谢性酸中毒的动物中，增加管腔流速均显著增强管腔氨的进入。相比之下，管腔pH在决定氨进入方面并非那么重要。这些研究中对管腔NH₃水平的分析与NH₃的简单扩散平衡不一致。在患有慢性代谢性酸中毒的动物中，进一步的研究表明抑制Na⁺-H⁺交换体对管腔氨的进入没有直接影响。然而，对用10 mmol/L氨灌注的小管的氨流出研究表明，NH₃和NH₄⁺均有显著转运。在对照条件下通过γ-谷氨酰转移酶对管腔谷氨酰胺脱酰胺作用的研究并未表明管腔产氨在体内浅表近端小管中起重要作用。这些以及最近关于近端小管氨转运的其他研究显著改变了传统的（NH₃）氨转运扩散平衡模型。管腔流速是管腔氨进入的一个重要决定因素。NH₄⁺进出小管腔的转运是总氨转运的一个主要组成部分。
