NH3 and NH4+ transport by rabbit renal proximal straight tubules.
NH3 and NH4+ transport by rabbit renal proximal straight tubules.
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NH3 和 NH4 通过兔肾近端直管转运。
DOI：
10.1152/ajprenal.1987.252.2.f232
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
Knepper,MA
中科院分区：
文献类型：
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作者：
Garvin,JL;Burg,MB;Knepper,MA
当灌注液和浴溶液含有1 mM NH 4Cl和25 mM碳酸氢盐（pH 7.4）时，从家兔中分离的灌注S2近端直小管自发分泌氨（-1.34 pmol X mm-1 X min-1）和吸收碳酸氢盐（49.3 pmol X mm-1 X min-1）。由于内腔中的pH较低，所收集的流体中的NH3浓度平均比浴中的NH3浓度低40%。为了测试NH3沿浴槽至管腔NH3浓度梯度的扩散是否可以解释所测量的氨分泌，我们测量了对NH3（1.6 X 10（-2）cm/s）和NH 4+（4.5 X 10（-5）cm/s）的渗透率。根据这些值，我们计算了被动NH3分泌（~ 3.6 pmol X mm-1 X min-1）和被动NH 4+吸收（0.9 pmol X mm-1 X min-1）的预测速率。预测的净氨分泌速率超过了测量的速率，表明被动NH3分泌可以完全解释测量的通量。在其他实验中，10（-4）M乙酰唑胺在浴和灌注液中抑制约80%的净碳酸氢盐吸收，但氨分泌速率不受影响。结论：S2近端直小管自发分泌氨，这是通过逆流倍增产生皮质髓质氨浓度梯度所需的。NH3沿着管腔酸化产生的浓度梯度向下扩散可以解释氨分泌。发生NH 4+的大量被动腔至浴回流。乙酰唑胺不抑制氨分泌。
Isolated perfused S2 proximal straight tubules from rabbits spontaneously secreted ammonia (-1.34 pmol X mm-1 X min-1) and absorbed bicarbonate (49.3 pmol X mm-1 X min-1) when perfusate and bath solutions contained 1 mM NH4Cl and 25 mM bicarbonate (pH 7.4). The NH3 concentration in the collected fluid was on average 40% lower than that of the bath as a consequence of a lower pH in the lumen. To test whether diffusion of NH3 down the bath-to-lumen NH3 concentration gradient could account for the measured ammonia secretion, we measured the permeabilities to NH3 (1.6 X 10(-2) cm/s) and NH4+ (4.5 X 10(-5) cm/s). From these values, we calculated predicted rates of passive NH3 secretion (-3.6 pmol X mm-1 X min-1) and passive NH4+ absorption (0.9 pmol X mm-1 X min-1). The predicted rate of net ammonia secretion exceeded the measured rate, indicating that passive NH3 secretion can fully account for the measured flux. In additional experiments, 10(-4) M acetazolamide in bath and perfusate inhibited net bicarbonate absorption by approximately 80%, but the rate of ammonia secretion was unaffected. Conclusions: S2 proximal straight tubules spontaneously secrete ammonia as required for generation of a corticomedullary ammonia concentration gradient by counter-current multiplication. Diffusion of NH3 down a concentration gradient created by luminal acidification can account for the ammonia secretion. A substantial passive lumen-to-bath backflux of NH4+ occurs. Acetazolamide does not inhibit ammonia secretion.