Pallone T L
Division of Nephrology, Milton S. Hershey Medical Center of Pennsylvania State University, Hershey 17033.
Am J Physiol. 1994 Jul;267(1 Pt 2):R260-7. doi: 10.1152/ajpregu.1994.267.1.R260.
Partially because of facilitated transport of urea, urea permeability (Pu) 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 Pu by 33%. When osmolarity due to thiourea was balanced by addition of mannitol or thiourea, similar results were obtained. Thiourea produced graded inhibition of Pu 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 Pu were compared by addition of 50 mM concentrations to the bath and perfusate. Thiourea and methylurea produced 32 and 34% inhibition of Pu, 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 Pu in a concentration-dependent fashion. It is concluded that a transporter confers high Pu to OMDVR. Pu 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.
部分由于尿素的易化转运，外髓质降支直小血管（OMDVR）的尿素通透性（Pu）常常超过钠通透性一个数量级以上。本研究对OMDVR尿素转运体进行了表征。将尿素类似物硫脲（200 mM）应用于微灌注OMDVR的管周表面，可使Pu降低33%。当通过添加甘露醇或硫脲来平衡由硫脲引起的渗透压时，也得到了类似的结果。随着硫脲浓度从0增加到100 mM，硫脲对Pu产生了分级抑制，从343±54（SE）降至191±43×10⁻⁵ cm/s。半数最大抑制所需的硫脲浓度为19 mM。通过向浴槽和灌注液中添加50 mM浓度的尿素类似物来比较它们降低Pu的能力。硫脲和甲基脲分别使Pu降低32%和34%，而尿素和乙酰胺分别仅使Pu降低3%和11%。随着跨膜尿素梯度从0增加到200 mM，转运体显示出可忽略不计的饱和现象。根皮素和对氯汞苯磺酸盐以浓度依赖的方式抑制Pu。得出的结论是，一种转运体赋予OMDVR高Pu。通过尿素流入或流出测量时，Pu同样很高。该转运体的特性与内髓集合管所表达的特性相似。
