NH4+ TRANSPORT IN RENAL INNER MEDULLARY COLLECTING DUCT

集合管在总的排泄中起主要作用 氨（NH3和NH 4+），主要的可调节成分， 尿净酸排泄 铵（NH 4+）分泌 集合管归因于并行的活跃质子分泌 随着NH3的被动扩散。 然而，我们的实验室 证明了NH 4+在终端内部的直接运输 髓集合管（tlMCD）。我们已经证明，NH 4 + 和钾离子竞争负钠离子上的一个共同结合位点 ATP酶活性降低，Na+泵抑制作用减弱 通过阻断Na +-的跨上皮净酸分泌 泵介导的NH 4+转运。 NH 4+的吸收 tlMCD的基底外侧膜由Naplus minusKplus - ATP酶，为管腔酸化提供了Hplus来源， 其他管腔缓冲液的滴定。 不像最近的 收集管节段，在tlMCD间质和管腔NH3 和NH 4+浓度已被测量。 因此，在本发明中， 转运蛋白介导的NH 4+通量可以被置于 已知的NH3和NH 4加梯度，以确定生理 Na+泵介导的NH 4+转运的作用。 但 尚不清楚体内Na+泵活性的变化是否调节 经上皮净酸分泌 如果整个组织的净酸分泌 顶膜在体内调节后增加， 预期穿过基底外侧膜的Hplus净摄取或 OH/HCO 3排出将平行增加。 该项目将 确定Na+泵数和Na+泵介导的离子 通过在体内给予醛固酮来调节转运。 我们 然后，将测试Na+泵活性是否与 总的和哇巴因敏感的NH 4+摄取和经上皮 净酸分泌。因此，我们将确定NH 4+的变化 体内摄取调节净酸分泌。 本提案的目的 在大鼠tlMCD中确定以下内容：1）如果 盐皮质激素增加Na+，K +-ATP酶介导的离子 运输和Na+泵数。 2)如果盐皮质激素 增加了NH 4+穿过基底外侧膜的吸收。 3)如果 盐皮质激素增加总酸和哇巴因敏感性净酸 4）如果盐皮质激素刺激其他基底外侧H 加上或OH/HCO 3运输途径，提供了一个来源， 用于顶端分泌的质子。 这些目标将使用 同位素和免疫印迹。 将使用灌注的tlMCD小管扩展观察， 体外

The collecting duct plays a major role in the excretion of total ammonia (NH3 and NH4 plus), the major regulatable component of urinary net acid excretion. Ammonium (NH4plus) secretion by the collecting duct is attributed to active proton secretion in parallel with the passive diffusion of NH3. However, our laboratory has demonstrated direct NH4plus transport in the terminal inner medullary collecting duct (tlMCD). We have shown that NH4plus and Kplus compete for a common binding site on the Naplus minus- ATPase and that inhibition of the Naplus pump decrease transepithelial net acid secretion through blockade o Na plus minus pump mediated NH 4 plus transport. Uptake of NH4 plus across the basolateral membrane of the tlMCD by the Naplus minusKplus - ATPase, provides a source of Hplus for luminal acidification and the titration of other luminal buffers. Unlike the m ore proximal collecting duct segments, in the tlMCD interstitial and luminal NH3 and NH4plus concentrations have been measured. Thus, transporter mediated NH4plus flux can be placed in context with known NH3 and NH4 plus gradients to determine the physiological role for Na plus pump-mediated NH 4 plus transport. However, it is not known if changes in Na plus pump activity in vivo regulate transepithelial net acid secretion. If net acid secretion across the apical membrane is increased following in vivo conditioning, it is expected that across the basolateral membrane net Hplus uptake or OH/HCO3 exit would increase in parallel. This project will determine if Na plus pump number and Na plus pump-mediated ion transport are regulated by aldosterone administration in vivo. We will then test if Na plus pump activity increases, in parallel, with both total and ouabain-sensitive NH4 plus uptake and transepithelial net acid secretion. Hence, we will establish if changes in NH4 plus uptake in vivo regulate net acid secretion. Aims of this proposal are to determine the following in the rat tlMCD: 1) If mineralocorticoid increases Na plus, K plus -ATPase-mediated ion transport and Na plus pump number. 2) If mineralocorticoid increases NH 4 plus uptake across the basolateral membrane. 3) If mineralocorticoid increases total and ouabain-sensitive net acid secretion and 4) If mineralocorticoid stimulates other basolateral H plus or OH/HCO3 transport pathways, providing a source of protons for apical secretion. The aims will be addressed using isotopes and immunoblots of tlMCD cells in suspension. Observations will be extended using tlMCD tubules perfused in vitro.