Benyajati S, Bay S M
Department of Physiology, College of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City 73190.
Am J Physiol. 1994 Mar;266(3 Pt 2):F439-49. doi: 10.1152/ajprenal.1994.266.3.F439.
The characteristics of taurine transport across renal basolateral membranes were examined, using basolateral membrane vesicles (BLMV) isolated from garter snake (Thamnophis spp.) kidneys. BLMV fraction exhibited high enrichment for the basolateral marker enzyme, Na(+)-K(+)-adenosinetriphosphatase (23-fold), with approximately 10% contamination by brush-border membranes. Taurine uptake into BLMV was specifically stimulated by inwardly directed Na+ gradient in the presence of Cl-. Equilibrium NaCl condition and replacement of NaCl gradient by KCl, choline chloride, NaSCN, sodium gluconate, or mannitol inhibited taurine uptake. Unlike brush-border membrane vesicles (BBMV), taurine uptake into BLMV was not stimulated by a Cl- gradient. In further contrast to BBMV, BLMV taurine uptake was smaller in magnitude and not electrogenic. The stoichiometric relationship between Na+ and BLMV taurine uptake, determined by activation method, indicated a 1 Na+:1 taurine interaction, in contrast to the 3 Na+:1 taurine stoichiometry for BBMV taurine transport. Bromcresol green inhibited BBMV taurine transport but had no effect on BLMV taurine uptake. Efflux of taurine from BLMV was faster than that from BBMV. Unlike BBMV, the BLMV efflux was stimulated by external taurine. The observed characteristics of taurine transport on both membranes would integratively result in net transepithelial reabsorption of taurine across renal cells of the garter snake, a species that demonstrates both net reabsorption and secretion of taurine in vivo.
利用从束带蛇（美洲束带蛇属）肾脏分离得到的基底外侧膜囊泡（BLMV），研究了牛磺酸跨肾脏基底外侧膜转运的特性。BLMV组分对基底外侧标记酶Na(+)-K(+)-三磷酸腺苷酶表现出高度富集（23倍），刷状缘膜污染约为10%。在Cl-存在的情况下，内向的Na+梯度可特异性刺激牛磺酸摄取到BLMV中。平衡NaCl条件以及用KCl、氯化胆碱、硫氰酸钠、葡萄糖酸钠或甘露醇替代NaCl梯度会抑制牛磺酸摄取。与刷状缘膜囊泡（BBMV）不同，Cl-梯度不会刺激牛磺酸摄取到BLMV中。与BBMV进一步不同的是，BLMV对牛磺酸的摄取量较小且不产生电效应。通过激活法确定的Na+与BLMV牛磺酸摄取之间的化学计量关系表明，二者的相互作用为1个Na+:1个牛磺酸，而BBMV牛磺酸转运的化学计量关系为3个Na+:1个牛磺酸。溴甲酚绿抑制BBMV牛磺酸转运，但对BLMV牛磺酸摄取没有影响。牛磺酸从BLMV中的流出速度比从BBMV中的流出速度快。与BBMV不同，外部牛磺酸可刺激BLMV的流出。在两种膜上观察到的牛磺酸转运特性综合起来会导致束带蛇肾细胞对牛磺酸进行净跨上皮重吸收，束带蛇在体内既表现出牛磺酸的净重吸收又表现出牛磺酸的分泌。
