Transepithelial Transport of Aliphatic Carboxylic Acids Studied in Madin Darby Canine Kidney (MDCK) Cell Monolayers

Transport of ¹⁴C-labeled acetic, propionic (PA), butyric, valeric, heptanoic (HA), and octanoic (OA) acids across the Madin Darby canine kidney (MDCK) epithelial cell monolayer grown on a porous polycarbonate membrane was studied in Hanks' balanced salt solution (HBSS) at 37°C in both apical-to-basolateral and basolateral-to-apical directions. At micromolar concentrations of solutes, metabolic decomposition was significant as evidenced by [¹⁴C]CO₂ production during the OA transport. The apparent permeability (Pe) indicates that as lipophilicity increases, diffusion across the unstirred boundary layer becomes rate limiting. In support of this notion, transport of OA and HA was enhanced by agitation, showed an activation energy of 3.7 kcal/mol for OA, and resulted in identical Pe values for both transport directions. Analysis of Pe changes with varying alkyl chain length resulted in a G of –0.68 ± 0.09 kcal/mol for –CH₂-group transfer from an aqueous phase to the MDCK cells. When the intercellular tight junctions were opened by the divalent chelator EGTA in Ca²⁺/Mg²⁺ -free HBSS, transport of the fluid-phase marker Lucifer yellow greatly increased because of paracellular leakage. PA transport also showed a significant increase, but OA transport was independent of EGTA. Although albumin also undergoes paracellular transport in the presence of EGTA and OA binds strongly to albumin, OA transport in EGTA solution was unchanged by albumin. These observations indicate that transmembrane transport is the major mechanism for lipophilic substances. The present study, together with earlier work on the transport of polar substances, shows that the MDCK cell monolayer is an excellent model of the transepithelial transport barrier.     

Electrical Analysis of Fresh,Excised Human Skin: A Comparison with Frozen Skin

Samples of human allograft skin prepared without freezing ("fresh skin) were found to have electrical and sodium ion transport properties which differed only slightly from those of skin which had been similarly treated but stored frozen (frozen skin). The fresh skin samples were less permeable to sodium ions during passive diffusion and less conductive than frozen skin at low current levels. They were more permselective for sodium versus chloride during constant-current iontophoresis and showed slightly more asymmetry in their current–voltage properties. Overall, the electrical behavior of the two tissues was similar enough to support the use of frozen tissue in iontophoresis studies. However, caution should be exercised when considering the use of frozen skin for applications, such as those based on electroosmosis, where the observed differences could have a major impact on the results.     

人钠/二羧基转运蛋白1在肾组织的表达变化及其与肾结石发病的关系

目的研究肾组织钠/二羧基转运蛋白1(hNaDC1)表达变化与肾结石发病的的关系.方法85例肾结石患者分为、尿枸橼酸正常结石组和低枸橼酸尿结石组.并设50例对照为非结石患者.采用RT-PCR及Northem印迹法检测其中部分肾结石患者肾组织的hNaDC1mRNA水平;免疫组化检测hNaDCl蛋白表达的变化;常规生化方法测定血、尿枸橼酸、草酸等生化指标.结果低枸橼酸尿结石组结石复发率(36.1%),显著高于尿枸橼酸正常结石组(16.3%,P＜0.01).hNaDC1mRNA在正常肾组织中有表达,分布于近端肾小管刷状缘;低枸橼酸尿结石患者hNaDC1mRNA/18sRNA比值(0.65±0.21)显著高于对照组(0.36±0.11,P＜0.01);而尿枸橼酸正常结石患者(0.4±0.13)与对照组比较差异无显著意义(P＞0.05);低枸橼酸尿结石组hNaDC1蛋白表达也显著高于对照组及尿枸橼酸正常结石组(P＜0.01),而后两组间差异无显著意义(P＞0.05).低枸橼酸尿结石组尿pH值、尿钠水平显著低于尿枸橼酸正常结石组和对照组;尿钙、尿草酸水平均显著高于对照组,与尿枸橼酸正常结石组无显著差异.结论肾组织hNaDC1表达上调可能是低枸橼酸尿的重要原因,与肾结石的形成和复发存在某种内在联系.     

降低隧道施工机械尾气污染的几项措施

目的　研究降低无轨运输方式施工隧道中空气污染的措施。方法　采用燃油添加剂 ,定期对施工机械进行维修和保养 ,减少发动机空档排气 ,将压入式通风口设置于距掌子面 8～ 10m处 ,保持通风管道密闭通畅致使有效送风。结果　隧道中有害气体CO、NOx及黑烟浓度至少降低 4 6 % ,55%和 4 2 %。结论　采取以上措施能明显改善施工环境的污染状况并减轻对施工人员身体健康的危害     

颅脑肿瘤手术行急性等容血液稀释的临床研究

目的：研究急性等容血液稀释对颅脑肿瘤病人血流动力学、氧转运及凝血纤溶方面的影响,探讨该方法的安全性。方法：选择颅脑肿瘤手术病人12例,麻醉后从右颈内静脉放置Swan～Ganz导管,从桡动脉放血8ml/kg,同时等速从静脉输入等量的海脉素。分别测定血液稀释前后的血流动力学,氧转运及凝血纤溶方面的指标。结果：CO、SV、DO2显著增加(P＜0.05);PT延长(P＜0.05);PLT较血液稀释前减少,其余指标无明显改变。结论：急性等容血液稀释对颅脑肿瘤病人的血流动力学及凝血纤溶功能影响小,而氧供增加,是一安全有效的血液保护方法。     

上海市中心城轨道交通网络规划合理规模研究

介绍了估算城市轨道交通网络规划规模的3种方法--几何分析法、运输强度分析法及类比分析法,并结合上海市的实际情况对上海市中心城轨道交通网络规划规模进行了估算。通过对比和分析各种估算结果,提出了上海市中心城轨道交通网络规划的合理规模。     

Comparison of the Disposition of Hepatically-Generated Morphine-3-glucuronide and Morphine-6-glucuronide in Isolated Perfused Liver from the Guinea Pig

Purpose. Humans and guinea pigs metabolise morphine extensively, forming the isomers morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) in relatively similar ratios. Both metabolites are formed in the liver, and their greater polarity relative to the parent aglycone may limit their permeability across hepatic membranes. This study compared the disposition of hepatically-generated M3G and M6G in perfused livers isolated from guinea pigs. Methods. Livers were perfused at 30 ml/min in a non-recirculating manner with Krebs bicarbonate buffer containing morphine (6 to 7 M). Perfusing medium, venous perfusate and bile were collected at regular intervals and concentrations of morphine, M3G and M6G determined by reversed-phase HPLC. Results. Concentrations of morphine, M3G and M6G in perfusate and the rates of biliary excretion of M3G and M6G were consistent between 20 and 50 min of perfusion. The mean (±s.d.) ratio for the rate of formation of M3G relative to M6G was 3.7 ± 1.5. A mean 33 ± 3% of morphine extracted by the liver was recovered as summed M3G and M6G. Of the M3G and M6G formed during a single passage, 19 ± 11% and 9 ± 9%, respectively, was excreted into bile; the values were significantly different (P = 0.002). Conclusions. A greater fraction of hepatically-generated M3G excreted into bile compared to that for M6G reflects differences in their relative transport across sinusoidal and canalicular membranes of hepatocytes, possibly via carrier-mediated systems.     

Solute Absorption from the Airways of the Isolated Rat Lung. IV. Mechanisms of Absorption of Fluorophore-Labeled Poly-α,β-[N(2-Hydroxyethyl)-DL-Aspartamide]

The pulmonary absorption kinetics of a single molecular weight distribution (MWD) of fluorophore-labeled poly-,-[N(2-hydroxyethyl)-DL-aspartamide] (F-PHEA), a hydrophilic and biocompatible synthetic polypeptide, were studied in the isolated, perfused rat lung (iprl) as functions of administered polymer concentration, dose, vehicle, and presence and absence of fluorophore. The MWD was characterized before and after absorption by measurement of weight- and number-averaged molecular weights (M _wand M _n, respectively) using high-performance gel-permeation chromatography. Values for M _w and M _n were 8.6 and 5.3 kD before, and 6.7 and 4.7 kD after, absorption into the perfusate; there was no significant metabolism and the MWD of the absorbed polymer was independent of both dose and sampling time over a 3-hr period. F-PHEA failed to show any evidence of aggregation in solution or changes in dose distribution within the airways as functions of increasing polymer concentration and dose. A concentration ranging study indicated the presence of a saturable, carrier-mediated transport process for F-PHEA with a maximum absorption rate, V _max, of approximately 180 µg or 0.027 µmol/hr. Coadministration of fluorophore-free PHEA was capable of depressing the absorption of F-PHEA. The transport process for F-PHEA appeared to have a molecular weight limit of about 7 kD for this hydrophilic polymer.     

Molecular Human Reproduction: Evidence for {gamma}-aminobutyric acid specific binding sites on human spermatozoa

The possible presence of -aminobutyric acid (GABA) specificbinding sites on human spermatozoa was investigated. Swim-uppreparations of human spermatozoa were incubated with radiolabelledGABA in the presence of unlabelled GABA, alternatively displacersof GABA_A/B receptors and GABA transport proteins. The resultsindicate that GABA specific binding sites are present on thesurface of human spermatozoa, and that these binding sites possiblyindicate the presence of GABA transport proteins. Furthermore,GABA at different concentrations was added to swim-up preparationsof human spermatozoa. Possible effects of GABA on sperm motility,hyperactivation and acrosome reaction were explored. No significantdifferences were observed between treated groups and controlsconcerning motility parameters and hyperactivation. Incubationwith GABA did not cause any increase in spontaneous acrosomereaction. However, spermatozoa treated with the calcium ionophoreA-23187 showed a small but significantly increased ability toundergo the acrosome reaction following preincubation in 10–⁴M GABA (P < 0.05).     

Steps to optimize transscleral photocoagulation

Background: In transscleral photocoagulation, the desired effect is coagulation of parts of the ciliary body or of the peripheral retina. However, the application is often limited by the unwanted effect of coagulation of the sclera. to reduce this effect, the ratio of incident radiation flux to radiation flux transported through the sclera (and able to coagulate the target tissue) should be minimized by the incident beam characteristics.Methods: Monte Carlo simulations for the radiation transport problem of multiple scattering in the sclera were used to calculate the ratio of transported to incident radiation for different parameter settings of beam diameters, optical thicknesses of the sclera and beam angles. To verify the theoretical calculations, an simple optical device utilizing a bulb instead of a laser source was constructed and applied to enucleated porcine eyes.Results: The theoretical calculations showed that the ratio of incident to transported radiation flux can typically be decreased by a factor of three by increasing the beam radius from 0.35 mm (as used in state-of-the-art laser devices) to 2 mm. This was confirmed by the experiments. Coagulations of the ciliary body or of the peripheral retina were possible with power densities an order of magnitude below the values normally applied with laser sources.Conclusion: To improve transscleral photocoagulation, beam diameters should be increased.