Knepper M A, Good D W, Burg M B
Am J Physiol. 1985 Dec;249(6 Pt 2):F870-7. doi: 10.1152/ajprenal.1985.249.6.F870.
We measured bicarbonate and ammonia transport by isolated perfused cortical collecting ducts from deoxycorticosterone-treated rats. With no ammonia in the perfusate and bath solutions, the collecting ducts secreted bicarbonate. The bicarbonate secretion was prevented when the rats were given 40 mM NH4Cl to drink. When 4 mM total ammonia was added to the perfusate and bath, the collecting ducts secreted ammonia and the direction of bicarbonate transport reversed toward absorption. Under those conditions the collected total ammonia concentration exceeded the value predicted by the diffusion-trapping model, assuming pH equilibrium. However, when carbonic anhydrase was added to the perfusate (to assure pH equilibrium), the collected total ammonia concentration decreased to the level predicted by the diffusion-trapping model. We conclude that rat cortical collecting ducts can secrete bicarbonate at substantial rates; the rate of bicarbonate secretion is modified by changes in the acid-base intake of the rats; ammonia secretion occurs by simple nonionic diffusion in this segment; the ammonia secretion is enhanced by the presence of acidic pH disequilibrium in the lumen; and ammonia in the perfusion and bath solutions inhibits bicarbonate secretion by rat cortical collecting ducts, a response that may be important for the regulation of renal bicarbonate excretion.
我们通过对脱氧皮质酮处理的大鼠分离灌注的皮质集合管来测量碳酸氢盐和氨的转运。在灌注液和浴液中无氨的情况下，集合管分泌碳酸氢盐。当给大鼠饮用40 mM氯化铵时，碳酸氢盐分泌被阻止。当向灌注液和浴液中添加4 mM总氨时，集合管分泌氨，并且碳酸氢盐转运方向逆转至吸收。在这些条件下，收集到的总氨浓度超过了扩散捕获模型在假设pH平衡时预测的值。然而，当向灌注液中添加碳酸酐酶（以确保pH平衡）时，收集到的总氨浓度降至扩散捕获模型预测的水平。我们得出结论，大鼠皮质集合管能够以相当大的速率分泌碳酸氢盐；碳酸氢盐分泌速率会因大鼠酸碱摄入量的变化而改变；在该节段氨通过简单的非离子扩散分泌；管腔内酸性pH失衡会增强氨的分泌；灌注液和浴液中的氨会抑制大鼠皮质集合管的碳酸氢盐分泌，这种反应可能对肾碳酸氢盐排泄的调节很重要。
