NH4+ TRANSPORT IN RENAL INNER MEDULLARY COLLECTING DUCT

收集管在总排泄中起主要作用。 氨(NH3和NH4+)，可调节的主要成分 尿净酸排泄量。细菌分泌的氨(NH4plus) 收集管归因于平行的活跃的质子分泌 NH3的被动扩散。然而，我们的实验室已经 演示了航站楼内部NH4+的直接运输 髓集合管(TlMCD)。我们已经证明了NH4plus 和Kplus竞争Naplus减号上的一个共同结合位点- ATPase与Naplus泵抑制作用下降 阻断Na+和Na+-阻断跨上皮净酸分泌 泵介导的NH4+转运。跨境吸收NH4+ Tl MCD的基底侧膜由Naplus减Kplus- ATPase，为管腔酸化提供了Hplus来源，并 其他管腔缓冲液的滴定。不同于矿体近端 收集管段，位于tlMCD间质和管腔NH3内 并测量了NH4+的浓度。因此， 转运体介导的NH4plus通量可以放在 已知的NH3和NH4加梯度来确定生理 Na+泵介导的NH4+转运作用。然而，它 目前尚不清楚体内Na+泵活性的变化是否调节 跨上皮网酸分泌。如果整个地球上的净酸分泌量 在活体条件作用后，顶膜增加，这是 预计跨过基底侧膜的净Hplus摄取或 OH/HCO3出口将平行增加。这个项目将 确定Na+泵浦次数和Na+泵浦介导的离子 转运受体内给予醛固酮的调节。我们 然后将测试Na+泵活动是否与 总的和哇巴因敏感的NH4+摄取和跨上皮 净分泌酸。因此，我们将确定NH4+是否发生变化 体内摄取调节净酸分泌。这项提议的目的 是为了确定老鼠tlMCD中的以下内容：1)如果 盐皮质激素增加Na+，K+-ATPase介导的离子 输送和钠加泵号。2)如果是盐皮质激素 增加跨基侧膜对NH4+的摄取。3)如果 盐皮质激素增加总酸量和哇巴因敏感型净酸 分泌和4)盐皮质激素是否刺激其他基底外侧H +或OH/HCO3运输途径，提供了 顶端分泌的质子。这些目标将通过以下方式实现 悬浮中tlMCD细胞的同位素和免疫印迹。 将使用tlMCD小管在 体外培养。

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.