CHARACTERIZATION OF THE UREA TRANSPORTER IN OUTER MEDULLARY DESCENDING VASA-RECTA
CHARACTERIZATION OF THE UREA TRANSPORTER IN OUTER MEDULLARY DESCENDING VASA-RECTA
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DOI：
10.1152/ajpregu.1994.267.1.r260
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发表时间：
1994-07-01
影响因子：
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通讯作者：
PALLONE, TL
中科院分区：
文献类型：
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作者：
PALLONE, TL
部分由于尿素的促进运输，直肠外髓降支(OMDVR)的尿素通透性(P-u)经常超过钠通透性一个数量级。本研究对OMDVR尿素转运体进行了表征。将200 mM的尿素类似物硫脲涂抹于微灌流OMDVR的腔面，可使P-u的抑制率达33%。当加入甘露醇或硫脲来平衡硫脲的渗透压时，也得到了类似的结果。随着浓度从0增加到100 mM，硫脲对P-u的抑制作用从343+/-54(SE)逐渐增加到191+/-43×10(-5)cm/S。半数抑制所需的硫脲浓度为19 mM。将50 mM浓度的尿素类似物加入浴液和灌流液中，比较它们降低P-u的能力。硫脲和甲基脲对P-u的抑制率分别为32%和34%，而尿素和乙酰胺的抑制率分别为3%和11%。当跨壁尿素梯度从0增加到200 mm时，转运体的饱和度可以忽略不计。Phloretin和对氯代苯磺酸汞以浓度依赖的方式抑制P-u。结论是，运输者赋予OMDVR较高的P-u。当用尿素流入或流出来衡量时，P-U也同样高。转运体的性质与内髓集合管所表达的性质相似。
Partially because of facilitated transport of urea, urea permeability (P-u) of the outer medullary descending vasa recta (OMDVR) frequently exceeds sodium permeability by more than an order of magnitude. This study characterizes the OMDVR urea transporter. Application of the urea analogue thiourea (200 mM) to the abluminal surface of microperfused OMDVR inhibited P-u by 33%. When osmolarity due to thiourea was balanced by addition of mannitol or thiourea, similar results were obtained. Thiourea produced graded inhibition of P-u from 343 +/- 54 (SE) to 191 +/- 43 x 10(-5) cm/s as concentration was increased from 0 to 100 mM. The thiourea concentration needed for half-maximal inhibition was 19 mM. The abilities of urea analogues to reduce P-u were compared by addition of 50 mM concentrations to the bath and perfusate. Thiourea and methylurea produced 32 and 34% inhibition of P-u, respectively, whereas urea and acetamide produced only 3 and 11% inhibition, respectively. The transporter showed negligible saturation as the transmural urea gradient was increased from 0 to 200 mM. Phloretin and p-chloromercuribenzenesulfonate inhibited P-u in a concentration-dependent fashion. It is concluded that a transporter confers high P-u to OMDVR. P-u is equally high when measured by urea influx or efflux. Properties of the transporter are similar to those expressed by the inner medullary collecting duct.