Hamm L L, Simon E E
Department of Medicine, Washington University School of Medicine, St. Louis, MO.
Miner Electrolyte Metab. 1990;16(5):283-90.
The transport of ammonia in the proximal tubule is a complex interaction of a number of processes. Ammonia transport in the proximal tubule is clearly bidirectional; ammonia is secreted into the early proximal tubule lumen, but later in the proximal tubule, efflux out of the lumen may result in net ammonia reabsorption. Two mechanisms of ammonia transport have clearly been established: NH3 diffusion and NH4+ transport on the Na(+)-H+ exchanger. The relative contribution of these pathways to ammonia transport is still unsettled. Other pathways for ammonia transport, particularly NH4+ efflux out of the lumen, may be important as well. A variety of factors may modulate ammonia transport: plasma, cell and luminal pH, luminal flow rate, luminal potassium, and angiotensin II. Each of these factors also alters ammonia production rates and in most circumstances, ammonia transport appears to follow ammonia production rates.
氨在近端小管中的转运是多种过程的复杂相互作用。氨在近端小管中的转运显然是双向的；氨分泌到近端小管起始段的管腔中，但在近端小管后期，从管腔中外流可能导致氨的净重吸收。氨转运的两种机制已明确确立：NH3扩散以及通过钠氢交换体进行的NH4+转运。这些途径对氨转运的相对贡献仍未确定。氨转运的其他途径，特别是氨从管腔中外流，可能也很重要。多种因素可调节氨转运：血浆、细胞和管腔pH值、管腔流速、管腔钾离子以及血管紧张素II。这些因素中的每一个也会改变氨的生成速率，并且在大多数情况下，氨转运似乎与氨生成速率一致。
