风湿性瓣膜病心房颤动患者右心房超极化激活电流密度及其通道表达的变化

目的 比较风湿性心脏瓣膜病心房颤动患者和窦性心律患者右心房单个心肌细胞超极化激活电流(If)密度及超极化激活的环核苷酸门控(HCN)通道表达的变化.方法 应用全细胞膜片钳技术记录25例房颤患者和16例窦性心律患者右心耳单个心房肌细胞If的变化,并用Westernblot法检测两组患者右心耳组织HCN通道的表达水平.结果 相同激活电位时,房颤组患者右心耳单个心房肌细胞If电流密度明显大于窦性心律组,且随电位增加激活更快,尤其在-70 mV时,房颤组和窦性心律组If电流密度分别为(-43.74±2.87)和(-26.81 ±1.41)pA/pF,此时两组比较差异有统计学意义(P＜0.01).房颤组HCN2、HCN4通道表达水平分别为0.44±0.20和0.53±0.20,与窦性心律组的0.23±0.13和0.36 ±0.18比较均明显增高(P＜0.01).结论 心房组织If电流密度增大及HCN通道表达上调参与了心房电重构,在房颤发生和维持中发挥作用.     

大鼠BMSCs体外诱导培养后连接蛋白40及超极化激活环核苷酸门控阳离子通道4表达的初步研究

目的观察大鼠BMSCs与窦房结组织块混合诱导培养后连接蛋白40(connexin 40,Cx40)及超极化激活环核苷酸门控阳离子通道4(hyperpolarization-activated cyclic nucleotide-gated cation channel 4,HCN4)的表达情况,探讨大鼠BMSCs向窦房结细胞诱导分化的可能性。方法 4～6周龄SD大鼠20只,雌雄不限,体重200～300 g。取6只SD大鼠,采用贴壁筛选法分离BMSCs,取第3代细胞以羧基荧光素二乙酸盐琥珀酰亚胺酯标记后,接种于6孔培养板内,同时制作细胞爬片。取14只SD大鼠窦房结组织,剪成0.3 cm×0.3 cm大小组织块,与标记后的第3代BMSCs混合培养,作为实验组;对照组仅单独培养第3代BMSCs。对照组培养1周及实验组混合培养1、2、3周,采用免疫组织化学方法检测Cx40和HCN4表达,并采用Image pro plus 5.0图像分析软件检测各组细胞表达Cx40和HCN4的平均积分吸光度值(mean integrated absorbance,MIA);采用实时荧光定量PCR检测细胞Cx40及HCN4 mRNA表达水平。结果免疫组织化学染色检测示,实验组混合培养1、2、3周,Cx40和HCN4 MIA值均显著高于对照组(P<0.01);且实验组随培养时间延长,Cx40和HCN4MIA值均逐渐增加,各时间点间差异均有统计学意义(P<0.05)。实时荧光定量.PCR检测示,实验组混合培养后1、2、3周,Cx40和HCN4 mRNA表达水平均显著高于对照组(P<0.01);实验组随培养时间延长,Cx40和HCN4 mRNA表达水平均逐渐增加,各时间点间差异均有统计学意义(P<0.05)。结论将大鼠BMSCs与窦房结组织块体外混合培养,诱导后细胞高表达Cx40及HCN4,具有向窦房结细胞分化的可能。     

Quantitative analysis and subcellular distribution of mRNA and protein expression of the hyperpolarization-activated cyclic nucleotide-gated channels throughout development in rat hippocampus

The properties of the hyperpolarization-activated current (I(h)) and its roles in hippocampal network function evolve radically during development. Because I(h) is conducted by the hyperpolarization-activated cyclic nucleotide-gated (HCN) cation channels, we tested the hypothesis that understanding the quantitative developmental profiles of HCN1, HCN2, and HCN4 expression, and the isoform- and age-specific progression of their subcellular distribution, should shed light on the established modifications of the properties of I(h) throughout development. Combined quantitative in situ hybridization, regional western blots, and high-resolution, dual-label immunocytochemistry revealed striking and novel information about the expression and distribution of the HCN channel isoforms in the developing hippocampal formation. In cornus ammon 1 (CA) pyramidal cell layer, a robust increase of HCN1 mRNA and protein expression occurred with age, with reciprocal reduction of HCN4 and relatively stable HCN2 levels. These distinct expression patterns raised the contribution of HCN1 to the total HCN channel pool from 33% to 65% consonant with acceleration and reduced cyclic adenosine mono phosphate (cAMP) sensitivity of I(h) in this region with age. In CA3, strong expression of HCN1 already neonatally supports the recently established role of this conductance in neonatal, age-specific, hippocampal oscillations (giant depolarizing potentials). Notably, HCN1 channels were present and probably transported to dendritic compartments already on postnatal day (P) 2, whereas HCN2 channel protein was not evident in dendrites for the first 2 weeks of life. HCN2 mRNA and protein expression remained fairly constant subsequent to the first week of life in all hippocampal subfields examined, whereas HCN4 mRNA and protein expression declined after maximal neonatal expression, so that the contribution of this isoform to the total HCN channel pool dropped from 43% (CA1) and 34% (CA3) on P11 to 8% (CA1) and 19% (CA3) on P90. Interneuronal expression of all HCN channel isoforms in stratum pyramidale was robust in parvalbumin-but not in cholecystokinin-expressing populations and with a subunit-specific subcellular distribution. Taken together, these data suggest that early in life, HCN4 may contribute significantly to the functions of I(h) in specific hippocampal regions. In addition, these evolving, differential quantitative, and subcellular expression patterns of the HCN channel isoforms support age-specific properties and functions of I(h) within the developing hippocampal formation.     

Localization of inward rectifier potassium channel Kir7.1 in the basolateral membrane of distal nephron and collecting duct

Inward rectifier potassium channels (Kir) play an important role in the K(+) secretion from the kidney. Recently, a new subfamily of Kir, Kir7.1, has been cloned and shown to be present in the kidney as well as in the brain, choroid plexus, thyroid, and intestine. Its cellular and subcellular localization was examined along the renal tubule. Western blot from the kidney cortex showed a single band for Kir7.1 at 52 kD, which was also observed in microdissected segments from the thick ascending limb of Henle, distal convoluted tubule (DCT), connecting tubule, and cortical and medullary collecting ducts. Kir7.1 immunoreactivity was detected predominantly in the DCT, connecting tubule, and cortical collecting duct, with lesser expression in the thick ascending limb of Henle and in the medullary collecting duct. Kir7.1 was detected by electron microscopic immunocytochemistry on the basolateral membrane of the DCT and the principal cells of cortical collecting duct, but neither type A nor type B intercalated cells were stained. The message levels and immunoreactivity were decreased under low-K diet and reversed by low-K diet supplemented with 4% KCl. By the double-labeling immunogold method, both Kir7.1 and Na(+), K(+)-ATPase were independently located on the basolateral membrane. In conclusion, the novel Kir7.1 potassium channel is located predominantly in the basolateral membrane of the distal nephron and collecting duct where it could function together with Na(+), K(+)-ATPase and contribute to cell ion homeostasis and tubular K(+) secretion.     

RACTK1: a putative inward rectifier potassium channel of the distal nephron. Investigation in Xenopus laevis oocytes

To date, cloning and examination of the functional properties of RACTK1, a K⁺ channel present in the distal nephron, have been performed in Chinese hamster ovary cells, but not using the oocyte expression system. We examined the expression and cytological localization of RACTK1 protein in Xenopus oocytes. In vitro transcribed cRNA of ROMK1, RACTK1, streptavidin‐tagged constructs of RACTK1 and ROMK1, alone or in concert, were injected into oocytes. Protein expression was evaluated by two‐electrode voltage clamp, followed by immunocytochemistry. ROMK1 and co‐injected oocytes (tagged and untagged) exhibited barium‐sensitive K⁺ conductances significantly greater than both RACTK1 (tagged and untagged) and water‐injected oocytes. Water‐injected oocytes failed to demonstrate protein expression. Expression of membrane protein was evident in ROMK1‐injected and RACTK1/ROMK1 co‐injected oocytes, but not in RACTK1‐injected oocytes. RACTK1 does not produce an extracellular membrane protein in oocytes. Therefore, this system is not suitable for further study or verification of the properties of RACTK1.     

Low-grade renal epithelial tumor originating from the distal nephron

There are few published reports of low-grade renal epithelial tumor originating from the distal nephron. However, it should not be disregarded clinically, because the actual number of patients with such tumors may be higher than expected. We investigated the immunohistochemical profile of a histologically distinct subtype of such a tumor in detail, in addition to the clinical course and imaging studies. The present study demonstrated that both glandular and spindle cell components of this tumor have a persistent characteristic of an epithelial tumor arising from the distal tubule or collecting duct. This tumor is a benign complex neoplasm that can be treated successfully with radical surgery. Beta-catenin and E-cadherin are suggested to play a crucial role in tumorigenesis and the biphasic arrangement of this neoplasm, concerning the expression of epithelial membrane antigen and carbohydrate antigen 19-9. We suggest that the term 'distal nephron epithelioma' is appropriate for classifying such rare but clinicopathologically distinct tumors.     

The connecting tubule: a functional subdivision of the rabbit distal nephron segments

Studies on adenylate cyclase response of the nephron fragments to hormones and drugs have suggested that there is a functionally distinct segment tentatively called the connecting tubule (CNT), which is located between the distal (DT) and the cortical collecting tubule (CCT). The functional significance of these biochemical findings was examined with isolated rabbit renal tubules perfused in vitro. The transepithelial voltage (PDt) of the DT, CNT, and CCT were, respectively, -28.7 +/- 3.24 mV (24), -27.0 +/- 2.69 mV (24), and -3.5 +/- 2.14 mV (11) in the normal rabbits. The PDt of the CCT increased to -32.2 +/- 2.02 mV (33) when rabbits were pretreated for at least 3 days with deoxycorticosterone acetate, DOCA (1 mg/kg/day, i.m.), whereas the PDt of the DT and the CNT remained unchanged. The PDt of the CCT obtained from deoxycorticosterone acetate- (DOCA) treated animals decreased after addition of antidiuretic hormone (ADH) or isoproterenol (ISO) to the bath. The PDt of the CNT also responded to these agents, but the dose required to obtain the same response was quite different: The CNT was 100-fold more sensitive to ISO as compared to the CCT, whereas the CCT was 10-fold more sensitive to ADH than was the CNT. In contrast, the PDt of the DT did not respond to any of these agents, even at a higher concentration. After addition of ADH (200 microU/ml) to the bath, the osmotic water permeability (10(-8) cm2 . sec-1 . atm-1) of the CCT increased from 1.13 +/- 0.83 to 7.46 +/- 2.36, but that of the CNT remained low (0.36 +/- 0.78 in control vs. 0.48 + 0.64 after ADH). These observations support the view that the CNT is functionally distinct from either the DT or the CCT.     

Reduced Na-K-ATPase in distal nephron in glycerol-induced acute tubular necrosis

To further characterize changes in tubular Na-K-ATPase in acute tubular necrosis (ATN), segmental analysis was performed in rat nephrons. Na-K-ATPase was assayed in the following segments: proximal convolution (PC), proximal straight (PS), outer medullary thick ascending limb (MTAL), cortical thick ascending limb (CTAL), distal convolution (DC) and cortical collecting duct (CCD) in three groups of rats: 1.) intact; 2.) moderate non-oliguric ATN; and 3.) severe oliguric ATN. GFR and CNa/GFR X 100 were in group 1 0.80 +/- 0.05 ml/min and 0.68 +/- 0.06, in group 2 0.14 +/- 0.02 and 1.46 +/- 0.35, and in group 3 0.04 +/- 0.01 and 0.46 +/- 0.15, respectively. Na-K-ATPase in PC and PS were similar in all three groups. Na-K-ATPase levels were in MTAL: in group 1 37 +/- 2 X 10(-11) mol/mm/min, in group 2 20 +/- 1 X 10(-11), P less than 0.001 versus group 1, and in group 3 24 +/- 2 X 10(-11), P less than 0.001 versus group 1. In CTAL Na-K-ATPase levels were: in group 1 40 +/- 2 X 10(-11), in group 2 33 +/- 1 X 10(-11), P less than 0.001 versus group 1, and in group 3 27 +/- 2 X 10(-11), P less than 0.001 versus groups 1 and 2.(ABSTRACT TRUNCATED AT 250 WORDS)     

A hypothesis linking sodium and lithium reabsorption in the distal nephron.

BACKGROUND: A hypothesis is proposed linking Na(+) and Li(+) reabsorption in the distal nephron. The handling of these two ions in the distal nephron is related because they share the same apical membrane entry mechanism: the amiloride-sensitive Na(+) channel (ENaC). However, the two ions exit the cell through different transport mechanisms: Na(+) via the Na(+)-K(+)-ATPase and Li(+) via the Na(+)/H(+) exchanger. Studies in rats have shown that under normal circumstances hardly any Li(+) is reabsorbed in the distal nephron, so that the urinary excretion of Li(+), expressed as a fraction of the delivery to the early distal tubule (FE(Li dist)), amounts to approximately 0.97. In contrast, during severe dietary Na(+) restriction, FE(Li dist) decreases to 0.50-0.60. Our hypothesis is that the absence of distal Li(+) reabsorption during intake of a normal diet can be explained by a negative driving force for Li(+) entrance across the apical membrane in those segments in which ENaC is active. METHOD: We propose a model that incorporates this concept. RESULTS: The model indicates that the lowering of FE(Li dist) during dietary Na(+) restriction can be explained by activation of apical ENaC in extra sub-segments further downstream. In these extra sub-segments the driving force for Li(+) reabsorption is positive, leading to significant Li(+) reabsorption. During dietary K(+) restriction, FE(Li dist) is reduced to 0.35-0.55. The model shows that this reduction in FE(Li dist) can be explained by hyperpolarization of the apical membrane in ENaC-containing sub-segments, which is known to occur in this condition. CONCLUSION: We conclude that the model may improve current understanding of both Na(+) and Li(+) handling in the distal nephron.     

Role of the aldosterone-sensitive distal nephron in the sodium retention associated with liver cirrhosis

The renal mechanisms underlying sodium retention during liver cirrhosis have been difficult to elucidate. Kim and associates describe a biphasic pattern of regulation of the renal epithelial sodium channel in the common bile duct ligation model, shedding some light on this issue.     

Influences of the N- and C-termini of the distal nephron inward rectifier, ROMK

The inward rectifying potassium channels of the ROMK family are present in the distal nephron of the kidney. These channels have two membrane spanning portions, between which lies a hydrophobic domain thought to confer the majority of the conductive properties of the channel. The N- and C-termini are both intracellular. In this paper we have examined the contribution of the N- and C-termini to the pore by examining the interaction of Cs+ with the channels. ROMK1 has an additional 19 amino acids on its N-terminus in comparison to ROMK2. The C-terminus of ROMK2 was extended by addition of a streptavidin tag (sfROMK2). Currents were measured following expression in Xenopus oocytes using two-electrode voltage clamp. ROMK1, ROMK2 and sfROMK2 exhibited concentration- and voltage-dependent block of inward currents by extracellular Cs+. The Hill coefficients were not significantly different from one. The mean Kd values at 0 mV were 100.6 +/- 10.6, 63.1 +/- 3.9 and 40.6 +/- 9.4, respectively (p < 0.05). The electric distances (delta) were 0.94 +/- 0.06, 1.0 +/- 0.05 and 1.37 +/- 0.06 respectively. The delta of sfROMK2 was greater than either ROMK1 or ROMK2 (p < 0.001). ROMK1, ROMK2 and sfROMK2 are sensitive to extracellular Cs+. Block was both concentration- and voltage-dependent. sfROMK2 is most Cs+-sensitive. ROMK1 contains an additional N-terminal 19 amino acids. Thus the pore properties of these two isoforms are subtly different, and influenced by the N-terminus. The lower Kd in sfROMK2 suggests that the streptavidin tag, and perhaps the C-terminus, also affect the pore.