低亲和力钠依赖二羧基转运蛋白随增龄表达变化的研究

目的 研究大鼠及人类肾脏低亲和力钠依赖(Na~+/)二羧基转运蛋白(NaDC1)随增龄的表达变化规律并探讨其在肾脏衰老变化中的意义。方法 采用Northern杂交、Western印迹及免疫组化等方法对大鼠出生后1d、7d、1个月、3个月、12个月、24个月及少年、中青年、老年正常人肾脏 NaDC1的表达变化。结果 大鼠NaDC1 mRNA表达呈现随肾组织发育成熟表达逐渐增强,1个月达高峰,后随增龄表达下降的趋势(P<0.05)。Western印迹显示NaDC1蛋白随鼠龄增高表达逐渐增强,3个月达高峰,后表达渐降的趋势。免疫组化结果显示大鼠及人类肾组织NaDC1分别表达于近端小管刷状缘,大鼠生后1d表达最弱,后表达渐强,到3个月达高峰(5.30±1.52比1.40±0.43,P<0.01),后呈现渐降的趋势(P<0.05)。人类肾组织NaDC1表达呈现随增龄渐降的趋势。结论 大鼠及人肾组织进入衰老时,NaDC1 mRNA及蛋白表达均呈现下降的趋势,可作为对肾脏衰老观察的指标之一。     

缺血再灌注损伤后肾小管上皮细胞的衰老演变及其意义

目的观察肾脏缺血再灌注损伤（IRI）后正常和衰老肾小管上皮细胞的演变，探讨细胞衰老在衰老相关性肾脏病理变化中的作用。方法以低龄（2月龄）和高龄（12月龄）野生鼠为研究对象。建立左肾IRI模型。于IRI后0d、1d、3d、7d、1月、3月、6月取肾组织，用HE染色观察肾小管组织学变化；免疫组织化学检测肾小管上皮细胞增殖细胞核抗原（PCNA）的表达；组织化学染色观察肾小管上皮细胞衰老相关β-半乳糖苷酶（SA-β-gal）的活性；TUNEL法检测凋亡肾小管上皮细胞。结果肾脏IRI后0d，肾小管以坏死为主，高龄鼠比低龄鼠更为明显（P〈0．05）。IRI1d后出现肾小管上皮细胞凋亡，7d凋亡达到高峰（P〈0．05），且在同一时间点，高龄鼠比低龄鼠严重（P〈0．05）。低龄鼠IRI肾1月时出现肾小管上皮细胞衰老，而对侧肾没有出现，3月、6月点衰老细胞显著增多（P〈0．05）；高龄鼠IRI后0d双肾均可见大量衰老的肾小管上皮细胞，但IRI肾的衰老细胞在IRIld后明显减少（P〈0．05），1月后又逐渐增多。6月后高龄鼠双肾衰老的肾小管上皮细胞几乎又达到同一水平。PCNA阳性染色细胞出现的几率两组相比差异无统计学意义（P〉0．05），但低龄组细胞增殖能力要强于高龄组。对高龄鼠IRI后1d点肾小管上皮细胞凋亡与衰老之间的相关分析显示，二者存在显著负相关（r=-0．82,P〈0．001）。结论IRI可促进正常肾小管上皮细胞衰老的进程。已经进入衰老状态的肾小管上皮细胞在遭受IRI刺激后，更易走向死亡[坏死和（或）凋亡]。肾小管上皮细胞的这种演变，在老化相关性肾脏病理变化发生和进展中可能发挥着重要作用。     

中国实验用小型猪肾小管的发育及各节段标志物的表达

目的:明确解剖和生理上与人非常接近的中国实验用小型猪肾脏发育过程中肾小管的形态学变化和肾小管各节段的特异性标志物。方法:采用高碘酸-希夫(PAS)染色和免疫荧光染色技术,系统观察中国实验用小型猪妊娠28～112d(E28d～E112d)和出生后1d、7d、14d、21d(P1d～21d),共17个不同时间点猪肾小管的发育及肾小管特异性标志物雪莲花凝集素(LTL)、水通道蛋白1(AQP1)、钙结合蛋白(calbindin)-D28k在肾小管不同节段的表达。结果:(1)中国实验用小型猪E28d可见后肾间充质和输尿管芽,即后肾已经开始发育;但这时还没有肾小管。E35d可见不同节段的肾小管,即肾小管已开始发育。从E35d～P14d(E112d仔猪出生),肾皮质均有生肾区存在,即不断有新的肾单位发生;P21d生肾区消失,即不再有新的肾单位产生。(2)①LTL在E28d表达在输尿管芽,E35d开始在近端小管表达,以刷状缘表达最为明显;表达由弱到强,由点状到线状。②AQP1在E28d未见表达,E35d开始表达;AQP1表达在近端小管和髓袢的降支细段,主要表达在细胞膜,尤其在管腔侧的表达更为明显。③Calbindin-D28k在E28d表达在输尿管芽,E35d开始表达在远端小管和集合管;Calbindin-D28k主要表达在细胞质,随着肾小管发育,表达逐渐增强。(3)发现集合管来源于输尿管芽,发源于输尿管芽的集合管从被膜下的生肾区一直延伸到肾髓质。结论:中国实验用小型猪妊娠35d可以见到不同节段肾小管。LTL、AQP1、Calbindin-D28k可以分别作为猪近端小管、髓袢、远端小管和集合管的标志物。     

intermedin预处理对大鼠肾脏缺血再灌注损伤修复和再生过程的作用

目的 探讨intermedin （IMD）预处理对大鼠肾脏缺血再灌注（IR）损伤修复和再生过程的作用。 方法 将Wistar大鼠按随机数字表法分为4组：假手术组（sham）、IR组、转空质粒组和转IMD组。在切除右肾后,转IMD组用超声微泡造影剂介导的基因转染方法将IMD真核质粒转染到大鼠肾组织,用RT-PCR和Western印迹法检测转染效率。转染成功后,制作肾脏IR损伤模型,分别于再灌注后1 d、2 d、3 d、4 d、7 d和14 d 6个时间点各取6只大鼠,留取血清及肾组织标本,常规检测血清BUN和Scr;HE和PAS染色观察肾组织的病理变化;免疫组化法观察肾小管上皮细胞的增殖程度。 结果 （1）转IMD组比转空质粒组的IMD蛋白和mRNA表达均增多（均P < 0.05）,且转IMD组7 d时表达最多,与转IMD组4 d时差异无统计学意义;（2）与sham组相比,IR组1 d和2 d时Scr和BUN均显著增高（P < 0.05）;与IR组相比,转IMD组显著下降（P < 0.05）;转空质粒组与IR组相比差异无统计学意义（P > 0.05）。（3）IR组、转空质粒组和转IMD组大鼠的肾小管均受损,但转IMD组的损伤较轻,均以2 d时病理损伤最重。（4）sham组肾小管和肾小球内几乎没有增殖细胞核抗原（PCNA）阳性细胞的表达;IR组和转空质粒组的PCNA阳性数在IR损伤1 d时开始增加,7 d时最多;转IMD组的PCNA阳性细胞数在IR损伤1 d时开始增加,3 d时最多。与IR组1~4 d相比,转IMD组的PCNA阳性细胞数显著增加（P < 0.05）;与IR组7 d相比,转IMD组7 d的PCNA阳性细胞数显著减少（P < 0.05）。 结论 IMD预处理可以促进肾小管上皮细胞增殖,加速肾脏IR损伤修复和再生。     

骨髓间质干细胞对大鼠急性肾小管损伤修复的促进作用

目的 观察骨髓间质干细胞(MSCs)对氯化汞(HgCl2)导致的急性肾小管损伤有无治疗作用，并探讨其可能的机制。 方法 建立HgCl2腹腔注射导致大鼠急性肾衰竭模型。SD大鼠分为MSCs组(HgCl2+MSCs)、生理盐水组(HgCl2+生理盐水)及正常对照组。7 d后，观察体重、生存率、肾功能、肾脏病理改变，进行增殖细胞核抗原(PCNA)、巨噬细胞标志物ED-1和增强绿色荧光融合蛋白(EGFP)免疫组织化学染色，用RT-PCR技术检测肾组织内细胞因子的表达情况，并观察EGFP转基因的MSCs在肾脏的分布情况。 结果 MSCs组在体重、生存率、肾功能、肾脏病理改变上，均明显好于生理盐水组；肾组织内PCNA+及ED-1+细胞数明显少于生理盐水组；促进肾小管损伤修复的生长因子表皮生长因子(EGF)、血小板源生长因子(PDGF)、肝细胞生长因子(HGF)在肾组织内表达明显高于生理盐水组，而促炎症因子TNF-α则明显低于生理盐水组。7 d时，间质干细胞在肾间质中偶尔可见到，而肾小管中未见。 结论 MSCs输注可促进HgCl2所致的急性肾小管损伤的修复，其作用机制可能是通过调节肾组织中细胞因子的分泌起作用，而非完全依靠转分化成肾小管上皮细胞。     

中性粒细胞明胶酶相关脂质运载蛋白对大鼠肾脏缺血再灌注损伤肾小管上皮细胞的保护作用

目的 探讨中性粒细胞明胶酶相关脂质运载蛋白(NGAL)对大鼠缺血再灌注损伤肾脏肾小管上皮细胞凋亡的保护作用及机制.方法 建立大鼠肾脏缺血再灌注模型,雄性SD大鼠随机分为对照组、缺血再灌注模型组、NGAL组 ;HE染色观察3组大鼠肾组织病理变化 ;TUNEL法检测肾小管上皮细胞凋亡 ;实时定量PCR、Western印迹法检测凋亡蛋白fas、bcl-2的表达变化.结果 与缺血再灌注模型组比较,NGAL组肾小管上皮细胞凋亡数量显著减少[(8.6±3.4)/HP比(20.8±3.7)/HP,P＜0.05] ;NGAL组肾组织fas mRNA(2.34±0.51比6.84±2.34,P＜0.05)、fas蛋白(0.65±0.05比0.95±0.08,P＜0.05)表达显著下调,bcl-2蛋白(0.33±0.05比0.24±0.03,P＜0.05)表达显著上调,但bcl-2 mRNA表达无明显改变.结论 NGAL对大鼠缺血再灌注损伤肾小管上皮细胞有保护作用,其作用可能与减少细胞凋亡、改变凋亡蛋白的表达有关.     

骨调素和单核细胞趋化蛋白在大鼠梗阻性肾病中的表达及可能作用

目的:探讨骨调素(OPN)和单核细胞趋化蛋白(MCP-1)在大鼠梗阻性模型中的表达及其在肾脏纤维化发病机制中的作用.方法:采用-单侧输尿管结扎制造梗阻性肾病模型,分别于造模后7 d、14 d取肾组织,应用HE染色观察肾脏病理改变,免疫组化方法检测肾组织畔OPN和MCP-1蛋白的表达,应用逆转录-聚合酶链式反应(RT-PCR)法观察肾组织中OPN mRNA和MCP-1 mRNA的变化.结果:OPN、MCP-1表达主要位于肾小管上皮细胞,随着梗阻时间的延长,肾组织中OPN、MCP-1蛋白和mRNA表达明显增加.结论:OPN、MCP-1蛋白和mRNA在梗阻性肾病大鼠肾组织表达明显增加介导炎症过程,参与肾间质纤维化.     

核因子-κB在狼疮肾炎肾组织中的表达及其意义

目的了解狼疮肾炎(LN)肾组织中核因子(NP)-κB的表达并探讨其与LN肾脏病理改变和肾功能损害的关系.方法以NF-κB亚基P65单抗为抗体,采用微波免疫组织化学染色(APAAP法)检测LN肾组织NF-κB表达,并进一步分析其与肾小球内C-myc蛋白表达、LN活动指数、肾脏病理和功能损害的关系.结果狼疮肾炎肾组织中NF-κB表达较正常肾组织显著增高,以WHOⅣ型为最显著.NF-κB在肾小球和肾小管均有表达,但小管表达更显著.LN肾组织NF-κB阳性细胞数与肾小球C-myc蛋白表达量、肾组织活动指数、肾脏病理改变和肾功能损害显著相关.结论NF-κB可能参与了LN的发病机制,肾组织中NF-κB的表达可作为反映狼疮肾组织活动病变和进行性肾损害的参考指标.     

内质网应激相关凋亡途径参与单侧输尿管梗阻大鼠肾间质纤维化

目的 探讨内质网应激（ERS）相关凋亡途径在单侧输尿管梗阻（UUO）大鼠肾间质纤维化发生、发展中的作用。 方法 健康雄性Wistar大鼠25只,按随机数字表法分为UUO模型组（n=18）和假手术组（n=7）,UUO模型组行左侧输尿管结扎术,假手术组仅分离输尿管不结扎,分别于术后3 d、7 d、14 d处死各组大鼠,行HE和Masson染色,观察肾脏病理变化;比色法测定肾组织羟脯氨酸（HYP）含量;免疫组化法检测α平滑肌肌动蛋白（α-SMA）;原位末端标记法（TUNEL）与DNA电泳观察肾小管间质细胞凋亡情况;RT-PCR法检测梗阻侧肾组织ERS相关分子葡萄糖调节蛋白78（GRP78）mRNA表达变化;Western印迹法分析凋亡相关蛋白半胱氨酸天门冬氨酸蛋白酶3（caspase-3）和GRP78的蛋白表达变化。 结果 与假手术组比较,UUO模型组肾脏病理改变加重,肾间质纤维化程度随梗阻时间延长逐渐加重,肾组织HYP含量显著升高（P < 0.05）,肾组织α-SMA也在肾小管间质细胞广泛表达,TUNEL染色及DNA琼脂糖凝胶电泳提示大量的肾小管间质细胞凋亡。UUO模型组GRP78 mRNA表达于术后3 d即发生显著上调,而蛋白表达在术后7 d开始出现显著变化,与假手术组差异均有统计学意义（均P < 0.01）;在此后观察期间内GRP78 mRNA和蛋白均持续高水平表达。模型组大鼠肾组织caspase-3的蛋白表达在UUO术后3 d即有显著上调（P < 0.05）,且随着梗阻时间延长进行性升高,于术后7 d、14 d增多更为显著,与假手术组差异均有统计学意义（P < 0.05）。相关分析显示GRP78蛋白表达与肾组织HYP含量和caspase-3蛋白表达均呈正相关（r = 0.657,P < 0.01;r = 0.714,P < 0.01）。 结论 UUO早期即可诱导ERS标志蛋白表达变化,触发ERS。长期ERS可诱导肾小管间质细胞凋亡;caspase-3介导的ERS相关凋亡途径可能参与了肾间质纤维化过程。     

梗阻性肾病大鼠肾小管间质进行性纤维化的监测

目的:探讨梗阻性肾病肾小管间质进行性纤维变性的发展过程。方法:建立大鼠单侧输尿管梗阻模型(UUO),采用免疫组化染色方法测其双侧肾形态学改变及胶原Ⅳ蛋白和α平滑肌肌动蛋白(α-SMA)的沉积;应用RT-PCR定性和半定量的方法测其金属蛋白酶组织抑制剂1(TIMP-1)mRNA、胶原ⅣmRNA的表达。结果:随着梗阻时间延长,梗阻侧肾脏肾小管间质变宽,肾小球无明显变化。梗阻肾内的胶原Ⅳ蛋白和α平滑肌肌动蛋白沉积增加,差异有统计学意义(P<0.05)。胶原ⅣmRNA、TIMP-1mRNA表达明显增加,差异有统计学意义(P<0.05);对侧肾脏各项指标变化差异无显著性。结论:该模型稳定可靠,能较好地体现梗阻性肾病中肾小管间质纤维化进行性发展过程。     

Kidney injury molecule-1 expression in transplant biopsies is a sensitive measure of cell injury

Kidney injury molecule-1 (KIM-1) is a specific histological biomarker for diagnosing early tubular injury on renal biopsies. In this study, KIM-1 expression was quantitated in renal transplant biopsies by immunohistochemistry and correlated with renal function. None of the 25 protocol biopsies showed detectable tubular injury on histologic examination, yet 28% had focal positive KIM-1 expression. Proximal tubule KIM-1 expression was present in all biopsies from patients with histological changes showing acute tubular damage and deterioration of kidney function. In this group, higher KIM-1 staining predicted a better outcome with improved blood urea nitrogen (BUN), serum creatinine, and estimated glomerular filtration rate (eGFR) over an ensuing 18 months. KIM-1 was expressed focally in affected tubules in 92% of kidney biopsies from patients with acute cellular rejection. By contrast, there was little positive staining for Ki-67, a cell proliferation marker, in any of the groups. KIM-1 expression significantly correlated with serum creatinine and BUN, and inversely with the eGFR on the biopsy day. Our study shows that KIM-1 staining sensitively and specifically identified proximal tubular injury and correlated with the degree of renal dysfunction. KIM-1 expression is more sensitive than histology for detecting early tubular injury, and its level of expression in transplant biopsies may indicate the potential for recovery of kidney function.     

Increased expression of p21 (WAF1/CIP1) cyclin-dependent kinase (CDK) inhibitor gene in chronic allograft nephropathy correlates with the number of acute rejection episodes

The p21 (WAF1/CIP1) cyclin-dependent kinase (CDK) inhibitor gene is considered to be the senescence marker in some recent publications. Expression of the gene was evaluated in 14 normal human kidney tissues of different ages and in nine chronically rejected renal allografts. All normal kidneys were negative for p21 expression. Glomerular, tubular and interstitial expression of the marker was detected in 88.9% ( P<0.0001) and vascular expression in 66.7% of chronically rejected grafts ( P<0.001). No correlation was found between the intensity of p21 expression and recipient age, donor age or number of human leukocyte antigen (HLA) mismatches. The marker was expressed more in grade 3 of chronic allograft nephropathy (CAN) than in grade 2 ( P=0.059 for glomerular score). Tubular expression of p21 was correlated with the number of acute rejections: P<0.05 for three vs one and two, and P=0.0046 for three vs no previous acute rejection episodes.     

Expression of p16INK4a and other cell cycle regulator and senescence associated genes in aging human kidney

BACKGROUND: Somatic cells in vitro have a finite life expectancy before entering a state of senescence. If this state has an in vivo counterpart, it could contribute to organ aging. We have previously shown that human kidney cortex displays telomere shortening with age. In the present study, we evaluated the relationship between renal age in humans and a number of phenomena associated with cellular senescence in vitro. METHODS: Human kidney specimens were obtained at 8 weeks to 88 years of age and were assessed for changes related to aging. RESULTS: We found that human kidneys expressed relatively constant levels of mRNAs for genes potentially related to senescence. Among the candidate genes surveyed, the cell cycle regulator p16INK4a emerged with the strongest association with renal aging for both mRNA and protein expression. Proliferation as measured by Ki-67 expression was inversely correlated with p16INK4a expression, compatible with a role for p16INK4a as an irreversible cell cycle inhibitor. Cyclooxygenase 1 and 2 (COX-1 and COX-2) mRNA expression was elevated in older kidneys, associated with increased protein expression. Comparison of gene expression with age-related histologic changes revealed that glomerulosclerosis correlated with p16INK4a and p53, whereas interstitial fibrosis and tubular atrophy were associated with p16INK4a, p53, COX-1, transforming growth factor-beta 1 (TGF-beta 1), and heat shock protein A5 (HSPA5). CONCLUSION: We conclude that some changes observed in cellular senescence in vitro do occur in human kidney with age, particularly in the renal cortex, in some cases correlating with histologic features. P16INK4a emerged with the most consistent correlations with age and histologic changes and inversely correlated with cell replication.     

Kidney aquaporin-2 expression during escape from antidiuresis is not related to plasma or tissue osmolality.

Recent results indicate that renal escape from vasopressin-induced antidiuresis is accompanied by a marked downregulation of whole kidney aquaporin-2 (AQP-2) protein and mRNA expression. However, in those studies, the escaped animals were also markedly hypo-osmolar compared to controls as a result of water loading during antidiuresis. The present studies evaluated whether systemic or local osmolality contributes to the downregulation of AQP-2 expression in this model. In the first study, two groups of 1-deamino-[8-D-arginine]-vasopressin (dDAVP)-infused rats were water-loaded; after establishment of escape, one group was then water-restricted for 4 d to reverse the escape, whereas the other group continued daily water loading. Whole kidney AQP-2 protein was measured by Western blotting, and inner medulla AQP-2 mRNA was determined by Northern blotting. Results were compared to dDAVP-infused rats fed solid chow. After 4 d of water restriction, urine volume decreased to the same level as in the rats on solid chow; however, plasma sodium concentrations and plasma osmolality remained low. Despite maintenance of significant hypo-osmolality, rats in which escape was subsequently reversed by water restriction reestablished high dDAVP-stimulated kidney levels of AQP-2 after 4 d of water restriction. In the second study, AQP-2 expression was evaluated in different regions of kidneys from water-loaded rats undergoing escape from antidiuresis. Despite markedly different interstitial osmolalities, significant downregulation of AQP-2 expression compared to dDAVP-infused control rats was seen in the inner medulla, outer medulla, and cortex. Thus, neither systemic nor interstitial osmolality appears to appreciably be correlated with downregulation of kidney AQP-2 expression during escape from antidiuresis. These results therefore suggest that additional vasopressin- and osmolality-independent factors, likely related to the effects of extracellular fluid volume expansion, also regulate kidney AQP-2 expression in rats.     

Molecular events in kidney ageing

PURPOSE OF REVIEW: Ageing of the kidney is a problem of clinical and basic interest. The problem of renal dysfunction and end-stage renal disease is a major burden on the health system, and old donor age is a major limitation on the use of donor organs and on survival of transplanted kidneys. Moreover, stresses linked to nephropathies, postoperative stress, inflammation and allograft rejection can lead to premature senescence of renal cells thus accelerating organ atrophy. Age-related and disease or stress-related nephron loss could reflect both the limited ability of epithelial cells to repair and replicate in the face of environmental stresses, and limitations on the number of cell replications caused by telomere shortening. Therefore, elucidating cellular senescence mechanisms is relevant to kidney diseases and kidney transplantation. RECENT FINDINGS: Recent findings suggest additive effects of replicative and environmental stress-induced senescence in cellular and organ ageing. In particular, ATM/p53/p21 and Ras/p38/p16 pathways have been shown to co-contribute to the overall cellular senescence, which is caused by extrinsic and intrinsic stimuli. Moreover, the role of epigenetic factors, including protein acylation/deacetylation, chromatin remodeling or caloric restriction, is the focus of recent studies on ageing and senescence. SUMMARY: Despite significant progress, cellular senescence is still better understood in vitro than in vivo. So far, p16 remains the best marker of chronological age in the kidney, and can be considered as an indicator of premature senescence caused by stresses or disease. The beneficial effects of caloric restriction on organ ageing and the role of histone acetylation in pathologic states in rodents are of considerable interest, and deserve future studies.     

Identification of ICAM-1-positive cells in the nongrafted and transplanted rat kidney--an immunohistochemical and ultrastructural study.

Cellular localization of intercellular adhesion molecule-1 (ICAM-1) in rat nongrafted intact kidneys and in transplanted kidneys was investigated using monoclonal anti-rat ICAM-1, 1A29. The major ICAM-1-positive cells in the nongrafted and isografted kidneys were endothelial cells in the large vessels and intertubular capillaries, as observed using light microscopy. A weak, but specific expression of ICAM-1 antigen was noted in the glomeruli, but the exact localization and cell type were not clearly discernible. In the allograft, the ICAM-1-positive cells found in the nongrafted and isografted kidneys also expressed ICAM-1 antigen. In addition, tubular epithelial cells at the luminal border and some infiltrating cells in the allograft expressed ICAM-1. In the allograft, some graft-infiltrating cells were shown to be lymphocyte function-associated antigen-1(LFA-1)-positive. As the nature of ICAM-1-positive cells in the infiltrates was unclear, we examined ICAM-1-positive cells using immunoelectron microscopy and the direct immunoperoxidase method. Glomerular endothelial cells, podocytes, and Bowman's capsular epithelial cells expressed ICAM-1 antigen in the nongrafted and transplanted kidneys. Among the infiltrating cells in the allograft, the major ICAM-1 positive cells were macrophagelike tissues, and some blastic lymphocytes also expressed ICAM-1. Only rarely did the proximal tubular cells express ICAM-1 antigen at the luminal surfaces in the intact kidney. In the allograft, the proximal, distal, and collecting ductular epithelial cells expressed ICAM-1 at the luminal surface, and in addition, the ICAM-1 antigen was also localized at the basal surfaces of some of the renal proximal tubular epithelial cells. The upregulated ICAM-1 expression in the allograft may accelerate graft rejection by augmenting adhesiveness of LFA-1-positive graft-infiltrating cells.     

Organic anion and cation transporter expression and function during embryonic kidney development and in organ culture models

Organic anion and cation transporters (OATs, OCTs, and OCTNs) mediate the proximal tubular secretion of numerous clinically important compounds, including various commonly prescribed pharmaceuticals. Here, we report determination of the ontogeny of these transporters and of NaP(i)2 and SGLT1, using quantitative polymerase chain reaction (QPCR) to determine expression levels of transporter genes in rat embryonic kidneys on each day of gestation from embryonic day (ed) 13 to ed18, in cultures of induced and uninduced metanephric mesenchyme (MM), and on each day of 1 week of whole embryonic kidney (WEK) culture. We also examined ontogeny of Oat1 protein expression in rat embryonic kidney by immunohistochemistry. Finally, we used uptake of fluorescein (FL) as a novel in vitro functional assay of OAT expression in WEK and MM. Developmental induction of OAT and OCT genes does not occur uniformly: some genes are induced early (e.g., Oat1 and Oat3, potential early markers of proximal tubulogenesis), and others after kidney development is relatively advanced (e.g., Oct1, a potential marker of terminal differentiation). The ontogeny of transporter genes in WEK and MM is similar to that observed in vivo, indicating that these organ culture systems may represent convenient in vitro models to study the developmental induction of OATs, OCTs, and OCTNs. Functional transport was evidenced by accumulation of FL in the developing tubule in WEK and MM organ cultures. Our findings on the renal ontogeny of OATs and OCTs could carry implications both for the development of more rational therapeutics for premature infants, as well as for our understanding of proximal tubule differentiation.