Cohen J J
Kidney Int. 1986 Jan;29(1):32-40. doi: 10.1038/ki.1986.5.
In the mammalian kidney, the use of the ratio, delta net T-Na+/delta Q-O2, provides an overestimate of the energy requirements for unidirectional active Na+ transport. In the proximal tubule, the overestimate of the energy cost for T-Na+ is due to these phenomena: (1) The "leaky" characteristics of the proximal tubule does not permit an accurate estimate to be made of the active fraction of the unidirectional flux of Na+. Thus, the net Na+ or net HCO3- reabsorption rate alone cannot be used to determine the stoichiometry for unidirectional extrusion of Na+ (with HCO3-) by the Na,K-ATPase, since backflux of HCO3- into the lumen occurs. (2) There is a moiety of active Na+ with Cl- along the pars recta. Whether this reabsorptive rate is altered and O2 uptake also changed when GFR or NaHCO3 reabsorption is varied is not yet known. (3) The occurrence of energy-requiring synthetic functions (substrate-interconversions) in the proximal tubule, coupled, in part, to the rate of Na+ entry into the proximal tubule cells, results in changes in renal O2 uptake proportional to some (undetermined) fraction of the change in Na+ reabsorption. The utilization of a portion of these reabsorbed substrates in endergonic syntheses must account for a portion of the Na+-stimulated suprabasal O2 uptake rate. Hence, the presence of synthetic functions in the proximal tubule also contributes to the overestimation of the energy value of net Na+ reabsorption when the ratio, delta net TNa-+/delta Q-O2, is used.(ABSTRACT TRUNCATED AT 250 WORDS)
在哺乳动物肾脏中，使用比率δ净T-Na⁺/δQ-O₂会高估单向主动Na⁺转运的能量需求。在近端小管中，对T-Na⁺能量消耗的高估是由于以下现象：（1）近端小管的“渗漏”特性使得无法准确估计Na⁺单向通量的主动部分。因此，仅净Na⁺或净HCO₃⁻重吸收率不能用于确定Na⁺,K⁺-ATP酶单向排出Na⁺（与HCO₃⁻一起）的化学计量，因为HCO₃⁻会回流到管腔中。（2）在近端小管直部有一部分主动Na⁺与Cl⁻一起重吸收。当肾小球滤过率（GFR）或NaHCO₃重吸收发生变化时，这种重吸收率是否改变以及O₂摄取是否也改变尚不清楚。（3）近端小管中存在需要能量的合成功能（底物相互转化），部分与Na⁺进入近端小管细胞的速率相关，导致肾脏O₂摄取的变化与Na⁺重吸收变化的某个（未确定）部分成比例。这些重吸收底物的一部分用于吸能合成，这必然占了Na⁺刺激的基底侧上方O₂摄取率的一部分。因此，当使用比率δ净TNa⁺/δQ-O₂时，近端小管中合成功能的存在也导致对净Na⁺重吸收能量值的高估。（摘要截短于250字）
