Magaldi A J, Oyamaguchi M N, Kudo L H, Rocha A S
Departamento de Clínica Médica, Faculdade de Medicina, Universidade de Säo Paulo, Brasil.
Pflugers Arch. 1992 Apr;420(5-6):544-50. doi: 10.1007/BF00374631.
Phosphate transport by the inner medullary collecting duct of normal rats was studied using an in vitro microperfusion technique. Net (Jnet), lumen-to-bath (Jlb) and bath-to-lumen (Jbl) phosphate fluxes were measured using 32PO4 as tracer, in the absence of net water absorption. A net absorption of phosphate (22.3 +/- 3.3 pmol cm-2 s-1) was observed by direct determination, and was similar to the difference between the Jlb and Jbl (57.7 +/- 8.2 and 32.2 +/- 1.5 pmol cm-2 s-1 respectively). The addition of amiloride (10 microM) to the perfusate did not change the Jlb of phosphate but blocked the efflux of sodium. Also, the withdrawal of sodium from the bath and perfusion solution did not change the Jlb of phosphate. In parallel, the addition of ouabain (10 mM) to the bath fluid decreased the Jlb of sodium more (37%) than the Jlb of phosphate (12%) and did not change the Jbl of phosphate. The addition of arsenate (10 microM) to the perfusate both in the presence and in the absence of sodium caused a decrease in Jlb, but Jbl remained unchanged, and parathyroid hormone (10 U) added to the bath did not change the Jlb. The increase in pH of the bath and perfusion fluid was associated with an increase in the Jlb of phosphate, and the decrease in pH was similarly followed by a decrease in phosphate efflux. The Jbl did not change with the pH alterations. These data demonstrate that a net phosphate absorption takes place in rat inner medullary collecting duct perfused in vitro and that this transport appears to be independent of sodium absorption and the action of parathyroid hormone. Moreover, a decrease in luminal and bath pH induces a decrease in phosphate efflux.
采用体外微灌注技术研究了正常大鼠内髓集合管的磷酸盐转运。在无净吸水的情况下，以32PO4为示踪剂测量净（Jnet）、管腔到浴液（Jlb）和浴液到管腔（Jbl）的磷酸盐通量。通过直接测定观察到磷酸盐的净吸收（22.3±3.3 pmol cm-2 s-1），这与Jlb和Jbl之间的差值相似（分别为57.7±8.2和32.2±1.5 pmol cm-2 s-1）。向灌注液中添加氨氯地平（10 μM）不会改变磷酸盐的Jlb，但会阻断钠的外流。此外，从浴液和灌注液中去除钠不会改变磷酸盐的Jlb。同时，向浴液中添加哇巴因（10 mM）对钠Jlb的降低幅度（37%）大于对磷酸盐Jlb的降低幅度（12%），且不会改变磷酸盐的Jbl。无论有无钠存在，向灌注液中添加砷酸盐（10 μM）都会导致Jlb降低，但Jbl保持不变，向浴液中添加甲状旁腺激素（10 U）不会改变Jlb。浴液和灌注液pH值的升高与磷酸盐Jlb的增加相关，pH值的降低同样伴随着磷酸盐外流的减少。Jbl不会随pH值变化而改变。这些数据表明，在体外灌注的大鼠内髓集合管中发生了磷酸盐的净吸收，且这种转运似乎独立于钠吸收和甲状旁腺激素的作用。此外，管腔和浴液pH值的降低会导致磷酸盐外流减少。
