Flessner M F, Wall S M, Knepper M A
Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892.
Am J Physiol. 1991 Feb;260(2 Pt 2):F264-72. doi: 10.1152/ajprenal.1991.260.2.F264.
We have measured NH3 and NH4+ permeability coefficients in collecting ducts from the cortex, outer medulla, and inner medulla of the rat kidney. Isolated collecting duct segments of the rat were perfused with bicarbonate-buffered solutions containing carbonic anhydrase to eliminate any pH disequilibrium in the tubule lumen. NH3 or NH4+ concentration gradients were set up between the bath and the lumen. By measuring the total CO2 and total ammonia concentrations in the bath, the perfusate, and collected fluid, the NH3 and NH4+ concentrations were determined. Then, using the flow rate in the tubule and the tubule dimensions, we calculated the apparent permeability in each collecting duct segment for NH3 and NH4+. The NH3 permeabilities were as follows: 0.002 cm/s in the inner medullary collecting duct, 0.012 cm/s in the outer medullary collecting duct, and 0.024 cm/s in the cortical collecting duct. The NH4+ permeabilities for all segments were on the order of 10(-5) cm/s or less. The relative permeability values for the two ammonium species are consistent with the view that the secretion observed in vivo in collecting ducts is due to passive diffusion of NH3 from the interstitium to the lumen of the duct, parallel with H+ secretion.
我们测量了大鼠肾脏皮质、外髓和内髓集合管中NH₃和NH₄⁺的渗透系数。用含碳酸酐酶的碳酸氢盐缓冲溶液灌注大鼠分离的集合管段，以消除肾小管管腔内的任何pH失衡。在浴槽和管腔之间建立NH₃或NH₄⁺浓度梯度。通过测量浴槽、灌注液和收集液中的总CO₂和总氨浓度，确定NH₃和NH₄⁺的浓度。然后，利用肾小管中的流速和肾小管尺寸，计算每个集合管段中NH₃和NH₄⁺的表观渗透率。NH₃的渗透率如下：内髓集合管为0.002 cm/s，外髓集合管为0.012 cm/s，皮质集合管为0.024 cm/s。所有段的NH₄⁺渗透率约为10⁻⁵ cm/s或更低。两种铵类物质的相对渗透率值与以下观点一致，即在体内集合管中观察到的分泌是由于NH₃从间质被动扩散到管腔，与H⁺分泌平行。
