Cellular mechanisms of hormone and drug interaction in ion transport in the nephron

(1)P-糖蛋白在近曲小管中的作用为了阐明P-gp在近曲小管中的功能意义，我们用来自对照组和P-gp基因敲除小鼠(mdr1a/ab(-))的近曲小管(PST)进行灌流。通过微量荧光法测定肾上皮细胞摄取罗丹明来评估转运蛋白的活性。在对照组动物中，罗巴明摄取的t1/2为34秒，P-gp阻断剂维拉帕米使其增加到434秒。相比之下，在KO小鼠中，未经任何治疗的t1/2为407秒，维拉帕米治疗后t1/2没有变化。KO小鼠反复给予地高辛可引起肾组织药物浓度升高。随后使用蛋白激酶C(PKC)刺激剂(PMA)、PKC抑制剂(星形孢子素，H-7)和PI3-激酶抑制剂(WORTOMANN，LY294002)的研究表明，P-gp的功能是通过同时需要PKC和PI3-激酶的过程介导的。(2)围产期从禽类到哺乳动物类型的尿液浓缩机制为了研究围产期上肢从粗段到细段的解剖变化与细胞凋亡的功能意义，我们采用了来自不同围产期的等长延髓肾单位节段。胎儿期观察到的髓质厚上肢的主动转运迅速转变为成年型细长上肢的氯离子选择性被动转运。内髓集合管的尿素转运体在胎儿期缺乏，而加压素敏感转运体在出生后不久就出现了。结论：禽类向哺乳类肾脏的过渡是获得较高尿液浓度的关键。

(1) Function of P-glycoprotein in the proximal tubuleTo clarify the functional significance of the P-gp in the proximal tubule, we perfused proximal straight tubule (PST) isolated from the control and the P-gp knockout mice (mdr1a/ab(-)(-)). The activity of the transporter was assessed by microfluorometry of rodamine uptake to the kidney epithelia. In the control animals, T1/2 of the rotamine uptake was 34 sec, and verapamil, a blocker of P-gp, increased the value to 434 sec. By contrast, in the KO mice, T1/2 was 407 sec without any treatments, and it was unchanged after verapamil. Repeated administration of digoxin to the KO mice caused to increase the concentration of the drug in the kidney tissue. Subsequent studies using a proteinkinase C (PKC) stimulant (PMA), PKC inhibitors (staurosporine, H-7), and PI3-kinase inhibitors (wortomannin, LY294002) revealed that the function of P-gp is mediated by processes requiring both PKC and PI3-kinase.(2) Transition from avian to mammalian-type urine concentrating mechanisms during perinatal periodTo study functional significance of anatomical changes in the ascending limb from thick segment to thin segment by apoptosis during perinel period, we perfused isotaled medullary nephron segments obtained from varying perinatal periods. Active transport in the medullary thick ascending lim observed in the fetal period rapidly changed to Cl selective passive transport observed in the adult type thin ascending limb. While urea transporter in the inner medullary collecting duct is lacking during fetal period, the vasopressin sensitive transporter becomes apparent soon after the birth. It is concluded that transition from avian to mammalia type kidney is essential for attaining high urine concentration.