Erythropoietin alters the pharmacokinetics of organic anions mainly eliminated by the kidney in rats.

Erythropoietin (EPO) is a cytokine originally used for its effects on the hematopoietic system, and is widely prescribed around the world. In the present study, the effects of EPO administration on p-aminohippurate (PAH, a prototype organic anion) pharmacokinetics and on the renal expression of PAH transporters were evaluated. Male Wistar rats were treated with EPO or saline (control group). After 42 h, PAH was administered, and plasma samples were obtained at different time points to determine PAH levels. PAH levels in renal tissue and urine were also assessed. The renal expression of PAH transporters was evaluated by Western blotting. EPO-treated rats showed an increase in PAH systemic clearance, in its elimination rate constant, and in urinary PAH levels, while PAH in renal tissue was decreased. Moreover, EPO administration increased the expression of the transporters of the organic anions evaluated. The EPO-induced increase in PAH clearance is accounted for by the increase in its renal secretion mediated by the organic anion transporters. The goal of this study is to add important information to the wide knowledge gap that exists regarding drug-drug interactions. Owing to the global use of EPO, these results are useful in terms of translation into clinical practice.

Track analysis of the passage of rhodamine-labeled liposomes across porcine jejunal mucus in a microchannel device.

AIM: To investigate how surface charge and hydrophilicity affect the mucopermeation of liposomes across intestinal mucus. METHODOLOGY: Rhodamine-labeled liposomes (∼120-130 nm) with different surface charges were investigated for their capacity to flux across fresh porcine jejunal mucus in a microchannel device. Fluorescent microscopy and tracking analysis were used to measure liposome movement, while fluorescence lifetime imaging microscopy was utilized to determine mucus pH. RESULTS: Mucopermeation was dependent on hydrophilicity and surface charge - anionic liposomes permeated more than cationic. The most cationic liposomal prototype agglomerated mucus. Presence of Na+, K+ and Mg2+ increased both speed and straightness of the pathways for all prototypes. Cationic but not anionic liposomes caused acidification (pH 2.5). CONCLUSION: Acidification caused by cationic liposomes explains their ability to interfere with mucus stability. Surface charge of liposomes strongly influences mucopermeation capability.

Drug Clearance from Cerebrospinal Fluid Mediated by Organic Anion Transporters 1 (Slc22a6) and 3 (Slc22a8) at Arachnoid Membrane of Rats.

Although arachnoid mater epithelial cells form the blood-arachnoid barrier (BAB), acting as a blood-CSF interface, it has been generally considered that the BAB is impermeable to water-soluble substances and plays a largely passive role. Here, we aimed to clarify the function of transporters at the BAB in regulating CSF clearance of water-soluble organic anion drugs based on quantitative targeted absolute proteomics (QTAP) and in vivo analyses. Protein expression levels of 61 molecules, including 19 ATP-binding-cassette (ABC) transporters and 32 solute-carrier (SLC) transporters, were measured in plasma membrane fraction of rat leptomeninges using QTAP. Thirty-three proteins were detected; others were under the quantification limits. Expression levels of multidrug resistance protein 1 (Mdr1a/P-gp/Abcb1a) and breast cancer resistance protein (Bcrp/Abcg2) were 16.6 and 3.27 fmol/µg protein (51.9- and 9.82-fold greater than in choroid plexus, respectively). Among those organic anion transporters detected only at leptomeninges, not choroid plexus, organic anion transporter 1 (oat1/Slc22a6) showed the greatest expression (2.73 fmol/µg protein). On the other hand, the protein expression level of oat3 at leptomeninges was 6.65 fmol/µg protein, and the difference from choroid plexus was within two-fold. To investigate oat1's role, we injected para-aminohippuric acid (PAH) with or without oat1 inhibitors into cisterna magna (to minimize the contribution of choroid plexus function) of rats. A bulk flow marker, FITC-inulin, was not taken up from CSF up to 15 min, whereas uptake clearance of PAH was 26.5 µL/min. PAH uptake was completely blocked by 3 mM cephalothin (inhibits both oat1 and oat3), while 17% of PAH uptake was inhibited by 0.2 mM cephalothin (selectively inhibits oat3). These results indicate that oat1 and oat3 at the BAB provide a distinct clearance pathway of organic anion drugs from CSF independently of choroid plexus.

Structural properties governing drug-plasma protein binding determined by high-performance liquid chromatography method.

The high-performance liquid chromatography (HPLC) method employing stationary phases immobilized with plasma proteins was used for this study to investigate the structural properties governing drug-plasma protein binding. A set of 65 compounds with a broad range of structural diversity (in terms of volume, hydrogen-bonding, polarity and electrostatic force) were selected for this purpose. The Abraham linear free energy relationship (LFER) analyses of the retention factors on the immobilized HSA (human serum albumin) and AGP (α1-acid glycoprotein) stationary phases showed that McGowan's characteristic molecular volume (V), dipolarity/polarizability (S) and hydrogen bond basicity (B) are the three significant molecular descriptors of solutes determining the interaction with immobilized plasma proteins, whereas excess molar refraction (E) is less important and hydrogen bond acidity (A) is not of statistical significance in both systems, for electrically neutral compounds. It was shown that ionised acids, as carboxylate anions, bind very strongly to the immobilized HSA stationary phase and that ionised bases, as cations bind strongly to the AGP stationary phase. This is the first time that the effect of ionised species on plasma protein binding has been determined quantitatively; the increased binding of acids to HSA is due almost entirely to acids in their ionised form.

Autocuidado do cuidador familiar de adultos ou idosos dependentes após a alta hospitalar / Self-care in family caregiver of dependent adults or elderly persons after hospital discharge / El autocuidado del cuidador familiar de adultos o ancianos dependientes tras el alta hospitalaria

Este artigo apresenta uma compreensão sobre o autocuidado do cuidador familiar segundo a teoria de Dorothea Orem. Resulta de uma pesquisa qualitativa com aporte da Teoria Fundamentada nos Dados, utilizando-se das técnicas de visita domiciliar, registro de notas de campo e entrevista semiestruturada com 11 cuidadores, após a internação de familiar em um Hospital Universitário de Minas Gerais. Foram obtidas quatro categorias, destacando uma categoria central, em torno da qual se analisaram as facilidades, dificuldades e estratégias para o autocuidado do cuidador. Entre as dificuldades, foram evidenciadas: tempo insuficiente para os cuidados com a saúde e, entre as facilidades, o apoio de outros familiares. As principais estratégias foram: apoio na fé; revezamento nos cuidados e recursos na comunidade. Concluiu-se que orientações no momento da alta e o acompanhamento de enfermagem após a alta contribuem para o autocuidado do cuidador, atuando sobre suas dificuldades e estimulando suas potencialidades.

This article presents an understanding concerning self-care in family caregivers according to Dorothea Orem's theory. Resulting from a qualitative research based on Grounded Theory, this work uses the techniques of home visiting, field notes and semistructured interviews with 11 caregivers after the hospitalization of a family member in a teaching Hospital located in Minas Gerais. Four categories were found and among them a central category is highlighted from which some facilities, difficulties and strategies for selfcare in caregiver were analyzed. Considering the difficulties, insufficient time for healthcare was noticed whereas the support from other family members appeared as a facility. The main strategies were: faith as a support; shift work in healthcare and community resources. This study demonstrated that hospital discharge guidelines and nursing follow-up after discharge were responsible for positive contributions to self-care in caregivers helping them to overcome their difficulties and enhancing their potentialities.

El artículo presenta una comprensión sobre el autocuidado del cuidador familiar, según la teoría de Dorothea Orem. Resulta de investigación cualitativa con aporte de la Teoría Fundamentada en los Datos, utilizándo se de las técnicas de visitas a domicilio; registro de apuntes de campo y entrevista semiestructurada, tras la internación de un familiar en un hospital universitario de Minas Gerais. Se llegó a cuatro categorías, señalando una categoría central, alrededor de la cual se analizaron las facilidades, dificultades y estrategias para el autocuidado del cuidador. Se evidenció, entre las dificultades, tiempo insuficiente para los cuidados con la salud y, entre las facilidades, el apoyo de otros familiares. Las principales estrategias fueron: apoyo en la fe, revezo en los cuidados y recursos en la comunidad. Se concluyó que orientaciones el momento del alta y el acompañamiento de enfermería tras el alta contribuyen para el autocuidado del cuidador, actuando sobre sus dificultades y estimulando sus potencialidades.

Influence of surface charge of gold nanorods on skin penetration.

BACKGROUND/PURPOSE: The skin plays an important role as a protective barrier against toxic environments and also is a route of drug administration. In spite of evidence for and interest in the skin penetration of nanoparticles, no study has examined the effect of nanoparticle surface charge on percutaneous absorption. In this study, we investigated the effect of surface charges of gold nanorods (GNs) on skin penetration. METHODS: Using transmission electron microscopy (TEM) and image analysis, we quantitatively measured the ability of GNs to penetrate the skin. RESULTS: Our results showed that the area density of the electron-dense dots of GNs, which penetrated into the stratum corneum, significantly increased for negatively charged GNs compared to those with a positive charge (P < 0.01). To investigate the percutanoues absorption of charged GNs, in vitro skin permeation studies were carried out using a Franz-type diffusion cell (FDC). The penetration of GNs through the skin was quantified by inductively coupled plasma mass spectrometry. Consistent with TEM observations, our penetration study using an FDC also revealed that negative particles were frequently detected in samples of receptor fluid at 48 h after exposure (P < 0.01). CONCLUSION: Together our results showed that anionic GNs penetrate skin better than cationic GNs.

Lymphatic trafficking kinetics and near-infrared imaging using star polymer architectures with controlled anionic character.

Targeted lymphatic delivery of nanoparticles for drug delivery and imaging is primarily dependent on size and charge. Prior studies have observed increased lymphatic uptake and retentions of over 48 h for negatively charged particles compared to neutral and positively charged particles. We have developed new polymeric materials that extend retention over a more pharmaceutically relevant 7-day period. We used whole body fluorescence imaging to observe in mice the lymphatic trafficking of a series of anionic star poly-(6-O-methacryloyl-D-galactose) polymer-NIR dye (IR820) conjugates. The anionic charge of polymers was increased by modifying galactose moieties in the star polymers with succinic anhydride. Increasing anionic nature was associated with enhanced lymphatic uptake up to a zeta potential of ca.-40 mV; further negative charge did not affect lymphatic uptake. Compared to the 20% acid-conjugate, the 40-90% acid-star-polymer conjugates exhibited a 2.5- to 3.5-fold increase in lymphatic uptake in both the popliteal and iliac nodes. The polymer conjugates exhibited node half-lives of 2-20 h in the popliteal nodes and 19-114 h in the deeper iliac nodes. These polymer conjugates can deliver drugs or imaging agents with rapid lymphatic uptake and prolonged deep-nodal retention; thus they may provide a useful vehicle for sustained intralymphatic drug delivery with low toxicity.

Evaluation of uptake and transport of cationic and anionic ultrasmall iron oxide nanoparticles by human colon cells.

Nanoparticles (NPs) are in clinical use or under development for therapeutic imaging and drug delivery. However, relatively little information exists concerning the uptake and transport of NPs across human colon cell layers, or their potential to invade three-dimensional models of human colon cells that better mimic the tissue structures of normal and tumoral colon. In order to gain such information, the interactions of biocompatible ultrasmall superparamagnetic iron oxide nanoparticles (USPIO NPs) (iron oxide core 9-10 nm) coated with either cationic polyvinylamine (aminoPVA) or anionic oleic acid with human HT-29 and Caco-2 colon cells was determined. The uptake of the cationic USPIO NPs was much higher than the uptake of the anionic USPIO NPs. The intracellular localization of aminoPVA USPIO NPs was confirmed in HT-29 cells by transmission electron microscopy that detected the iron oxide core. AminoPVA USPIO NPs invaded three-dimensional spheroids of both HT-29 and Caco-2 cells, whereas oleic acid-coated USPIO NPs could only invade Caco-2 spheroids. Neither cationic aminoPVA USPIO NPs nor anionic oleic acid-coated USPIO NPs were transported at detectable levels across the tight CacoReady™ intestinal barrier model or the more permeable mucus-secreting CacoGoblet™ model.

The impact of hepatic uptake on the pharmacokinetics of organic anions.

The disposition of seven marketed and two AstraZeneca acid (organic anion) compounds with a range of volume of distribution at steady state (V(ss)) and clearance have been profiled in rat and dog. Pharmacokinetic (PK) parameters along with liver and muscle tissue levels were collected, and their contributions to total V(ss) were calculated. The physiologically based prediction of V(ss) correlated (all predictions within 2-fold) with the V(ss) obtained from plasma PK analysis. The V(ss) of the acid drugs with atypically high values could be explained by significant sequestering of compound to the liver. A "media loss" in the in vitro hepatocyte assay that monitors loss of compound from the incubation media along with physiologically based PK (PBPK) modeling was assessed for its ability to accurately predict the impact of hepatic uptake on both clearance and V(ss). This methodology significantly improved the prediction of metabolic in vivo clearance compared with standard hepatocyte scaling approaches that do not take into account hepatic uptake. Predictions of V(ss) from the media loss assay also correlate with the measured values from plasma PK analysis. However, hepatic uptake will have little overall impact on half-life, because of the concomitant impact on both Cl and V(ss), as long as hepatic extraction is not high. The methodology described here is particularly useful when there is no allometric relationship between species as a result of interspecies differences in liver uptake. In this situation, the potential use of human hepatocytes combined with PBPK modeling avoids the question of which species pharmacokinetics is most predictive to humans.

Polyvalent catanionic vesicles: exploring the drug delivery mechanisms.

Among drug delivery systems, catanionic vesicles now appear as powerful candidates for pharmaceutical applications because they are relatively cheap and easy to use, thus well corresponding to industrial requirements. Using labelled vesicles made of a tricatenar catanionic surfactant, the work reported here aims at exploring the mechanisms by which internalisation into a cell occurs. The study was performed on various cell types such as phagocytic as well as non-phagocytic cells using confocal laser scanning microscopy and flow cytometry. Using various inhibitors, endocytosis and also a passive process, as probably fusion, were highlighted as interaction phenomena between catanionic vesicles and cell membranes. Finally, the interaction modelled with giant liposomes as membrane models confirmed the hypothesis of the occurrence of a fusion phenomenon between the nanovectors and cell membranes. This process highlights the potential of catanionic vesicles for a future pharmaceutical application as a universal drug delivery system.

Gap junction permeability: selectivity for anionic and cationic probes.

Gap junction channels formed by different connexins exhibit specific permeability to a variety of larger solutes including second messengers, polypeptides, and small interfering RNAs. Here, we report the permeability of homotypic connexin26 (Cx26), Cx40, Cx43, and Cx45 gap junction channels stably expressed in HeLa cells to solutes with different size and net charge. Channel permeability was determined using simultaneous measurements of junctional conductance and the cell-cell flux of a fluorescent probe. All four connexins allowed passage of both cationic and anionic probes, but the transfer rates were connexin dependent. The negatively charged probes [Lucifer yellow (LY; median axial diameter 9.9 Å, charge -2), carboxyfluorescein (CF; 8.2 Å; -2), and Alexa Fluor350 (AF350, 5.4 Å; -1)] exhibited the following permeability order: Cx43 > Cx45 > Cx26 > Cx40. In contrast, for the positively charged species permeability, the orders were as follows: Cx26 ≈ Cx43 ≈ Cx40 ≈ Cx45 for N,N,N-trimethyl-2-[methyl-(7-nitro-2,1,3-benzoxadiol-4-yl) amino] ethanaminium (NBD-m-TMA; 5.5 Å, +1) and Cx26 ≥ Cx43 ≈ Cx40 > Cx45 for ethidium bromide (10.3 Å, +1). Comparison of probe permeability relative to K(+) revealed that Cx43 and Cx45 exhibited similar permeability for NBD-m-TMA and AF350, indicating weak charge selectivity. However, lesser transfer of CF and LY through Cx45 relative to Cx43 channels suggests stronger size-dependent discrimination of solute. The permeability of NBD-m-TMA for Cx40 and Cx26 channels was approximately three times higher than to anionic AF350 despite the fact that both have similar minor diameters, suggesting charge selectivity. In conclusion, these results confirm that channels formed from individual connexins can discriminate for solutes based on size and charge, suggesting that channel selectivity may be a key factor in cell signaling.

Tuning payload delivery in tumour cylindroids using gold nanoparticles.

Nanoparticles have great potential as controllable drug delivery vehicles because of their size and modular functionality. Timing and location are important parameters when optimizing nanoparticles for delivery of chemotherapeutics. Here, we show that gold nanoparticles carrying either fluorescein or doxorubicin molecules move and localize differently in an in vitro three-dimensional model of tumour tissue, depending on whether the nanoparticles are positively or negatively charged. Fluorescence microscopy and mathematical modelling show that uptake, not diffusion, is the dominant mechanism in particle delivery. Our results indicate that positive particles may be more effective for drug delivery because they are taken up to a greater extent by proliferating cells. Negative particles, which diffuse more quickly, may perform better when delivering drugs deep into tissues. An understanding of how surface charge can control tissue penetration and drug release may overcome some of the current limitations in drug delivery.

[The role of ABC transporters in the renal elimination of organic anions and drugs]. / Rola transporterów ABC w nerkowym wydalaniu organicznych anionów i leków.

The ATP-binding cassette (ABC) transporters are a large superfamily of integral membrane proteins that actively transport organic ions across biological membranes. These transporters play important role in the reabsorptive and excretory capacity of the kidney. Nine structurally and functionally related members (MRP1-7, P-gp, BCRP) have been identified, which differ from each other by their localization, expression levels, and substrate specificity. This review discusses current knowledge on the renal characteristics of ABC transporters, with specific focus on their regulation.

Sex-specific extraction of organic anions by the rat liver.

The capacity for hepatic elimination of some compounds is different in males and females and differential expression of a number of sinusoidal and canalicular transporters exists. However, the specific events underlying the functional differences are not understood. To determine how sex influences sinusoidal and canalicular organic anion transport, bile duct-cannulated livers from mature Sprague-Dawley rats of both sexes were single-pass perfused with saline containing the model organic anions bromosulphophthalein (BSP), carboxyfluorescein (CF), carboxyfluorescein diacetate (CFDA) or 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS). Assay of effluent perfusate anion concentration showed that BSP, but not DIDS, extraction was significantly higher in male versus female rats. At 20 min perfusion with 50 microM BSP the mean effluent concentration was 5.6 and 20.1 microM in, respectively, male and female rats. HPLC confirmed that the effluent perfusate concentration of BSP was higher in female as compared with male rats and was not contributed to by its glutathione conjugate. With 25 microM DIDS, the effluent concentration reached 7.3 (male) and 8.2 microM (female), indicating high extraction efficiency. In contrast to BSP and DIDS, CF extraction was very low (<20%) so that differences between male and females could not be assessed. Biliary BSP and CF excretion were, respectively, 3.5- and 4-fold higher in male rats. Neither sinusoidal efflux nor biliary excretion of CF was sex-dependent with a higher cytoplasmic load of CF (during CFDA perfusion). Our results suggest that differences in sinusoidal uptake are responsible for the sex-specific hepatic excretion of some organic anions.

The influence of macrolide antibiotics on the uptake of organic anions and drugs mediated by OATP1B1 and OATP1B3.

Macrolides may cause severe drug interactions due to the inhibition of metabolizing enzymes. Transporter-mediated uptake of drugs into cells [e.g., by members of the human organic anion transporting polypeptide (OATP) family] is a determinant of drug disposition and a prerequisite for subsequent metabolism. However whether macrolides are also inhibitors of uptake transporters, thereby providing an additional mechanism of drug interactions, has not been systematically studied. The human OATP family members OATP1B1 and OATP1B3 mediate the uptake of endogenous substances and drugs such as antibiotics and HMG-CoA reductase inhibitors (statins) into hepatocytes. In this study we investigated the potential role of these uptake transporters on macrolide-induced drug interactions. By using sulfobromophthalein (BSP) and the HMG-CoA reductase inhibitor pravastatin as substrates, the effects of the macrolides azithromycin, clarithromycin, erythromycin, and roxithromycin and of the ketolide telithromycin on the OATP1B1- and OATP1B3-mediated uptake were analyzed. These experiments demonstrated that the OATP1B1- and OATP1B3-mediated uptake of BSP and pravastatin can be inhibited by increasing concentrations of all macrolides except azithromycin. The IC50 values for the inhibition of OATP1B3-mediated BSP uptake were 11 microM for telithromycin, 32 microM for clarithromycin, 34 microM for erythromycin, and 37 microM for roxithromycin. These IC50 values were lower than the IC50 values for inhibition of OATP1B1-mediated BSP uptake (96-217 microM). These macrolides also inhibited in a concentration-dependent manner the OATP1B1- and OATP1B3-mediated uptake of pravastatin. In summary, these results indicate that alterations of uptake transporter function by certain macrolides/ketolides have to be considered as a potential additional mechanism underlying drug-drug interactions.

Development of synthetic membrane transporters for anions.

The development of low molecular weight anion transporters is an emerging topic in supramolecular chemistry. The major focus of this tutorial review is on synthetic chloride transport systems that operate in vesicle and cell membranes. The transporters alter transmembrane concentration gradients, and thus they have applications as reagents for cell biology research and as potential chemotherapeutic agents. The molecular designs include monomolecular channels, self-assembled channels and mobile carriers. Also discussed are the experimental assays that measure transport rates across model bilayer membranes.

Function of both sinusoidal and canalicular transporters controls the concentration of organic anions within hepatocytes.

We hypothesized that the function of both sinusoidal and canalicular transporters importantly controls the concentrations of organic anions within normal hepatocytes. Consequently, we investigated how acute transport regulation of the sinusoidal organic anion transporting polypeptides (Oatps) and the canalicular multidrug resistance associated protein 2 (Mrp(2)) determines the hepatic concentrations of the organic anion gadolinium benzyloxypropionictetraacetate (BOPTA) in rat livers. Livers were perfused with labeled BOPTA in different experimental settings that modify the function of Oatps and Mrp(2) through the protein kinase C (PKC) pathway. Intrahepatic concentrations were continuously measured with a gamma probe placed above rat livers. Labeled BOPTA was also measured in perfusate and bile. We showed that when the function of Oatps and Mrp(2) is modified in such a way that BOPTA entry and exit are similarly decreased, concentrations of organic anions within hepatocytes remain unaltered. When exit through Mrp(2) is abolished, hepatic concentrations are high if entry through Oatps is only slightly decreased (livers without Mrp(2) expression) or low if BOPTA uptake is more importantly decreased (livers perfused with a PKC activator). These results highlight that the function of both sinusoidal and canalicular transporters is important to determine the concentration of organic anions within hepatocytes.

Plasma separation and anion adsorption transiently relieve intractable pruritus in primary biliary cirrhosis.

BACKGROUND/AIMS: Pruritus can be a severely disabling symptom in patients with primary biliary cirrhosis who do not respond to treatment with ursodeoxycholic acid, anion exchangers, enzyme inducers, or opiate antagonists. The aim of this study was to assess the clinical efficacy of plasma separation and anion adsorption in the treatment of intractable pruritus of cholestasis. METHODS: Three patients with primary biliary cirrhosis and intractable pruritus defined by severity of pruritus 7 on a rating scale between 0 (no pruritus) and 10 (maximal pruritus) on at least 4 of 7 days despite medical treatment were treated with plasma separation and anion adsorption on three consecutive days. Fatigue was assessed using the Fisk Fatigue Severity Score and quality of life was assessed by the PBC-40, a disease specific health related quality of life measure. RESULTS: Improvement in pruritus, fatigue, and quality of life was transiently observed in all patients. Serum bile acid levels showed no association with intensity of pruritus, and the bile acid pattern was not altered. The treatment was well tolerated by all patients. CONCLUSIONS: Plasma separation and anion adsorption seem to be a safe and effective therapeutic option for patients with primary biliary cirrhosis suffering from intractable pruritus.

Increased glomerular permeability to negatively charged Ficoll relative to neutral Ficoll in rats.

It is established that the glomerular filter sieves macromolecules based on their size, shape, and charge. Anionic proteins are thus retarded compared with their neutral or cationic counterparts. However, recent studies have indicated that charge effects are small, or even "anomalous," for polysaccharides. We therefore investigated the impact of charge on the glomerular permeability to polysaccharides by comparing sieving coefficients (theta; primary urine-to-plasma concentration ratio) for negatively charged, carboxymethylated (CM) FITC-Ficoll and FITC-dextran with their neutral counterparts. For these probes, theta were determined in anesthetized Wistar rats [269 +/- 2.7 g (+/-SE; n = 36)], whose ureters were cannulated for urine sampling. The glomerular filtration rate was assessed using FITC-inulin. Polysaccharides were constantly infused, and after equilibration, urine was collected and a midpoint plasma sample was taken. Size and concentration determinations of the FITC-labeled polysaccharides were achieved by size-exclusion HPLC (HPSEC). For CM-Ficoll, theta was significantly increased (32 times at 55 A) compared with that of uncharged Ficoll. A small increase in theta for CM-dextran compared with neutral dextran was also observed (1.8 times at 55 A). In conclusion, negatively charged Ficoll relative to neutral Ficoll was found to be markedly hyperpermeable across the glomerular filter. Furthermore, negatively charged Ficoll was observed to be larger on HPSEC compared with its neutral counterpart of the same molecular weight. It is proposed that the introduction of negative charges in the "dendrimeric," cross-linked Ficoll molecule may alter its configuration, so as to make it more extended, and conceivably, more flexible, thereby increasing its glomerular permeability.

Cl- channels of the distal nephron.

Cl- currents were observed under whole cell clamp conditions in cells of the rat cortical collecting duct (CCD), connecting tubule (CNT), and thick ascending limb of Henle's loop (TALH). These currents were much larger in intercalated cells compared with principal cells of the CCD and were also larger in the TALH and in the CNT compared with the CCD. The conductance had no strong voltage dependence, and steady-state currents were similar in inward and outward directions with similar Cl- concentrations on both sides of the membrane. Current transients were observed, particularly at low Cl- concentrations, which could be explained by solute depletion and concentration in fluid layers next to the membrane. The currents had a remarkable selectivity among anions. Among halides, Br- and F- conductances were only 15% of that of Cl-, and I- conductance was immeasurably small. SCN- and OCN- conductances were approximately 50%, and aspartate, glutamate, and methanesulfonate conductance was approximately 5% that of Cl-. No conductance could be measured for any other anion tested, including NO3-, HCO3-, formate, acetate, or isethionate; NO3- and I- appeared to block the channels weakly. Conductances were diminished by lowering the extracellular pH to 6.4. The properties of the conductance fit best with those of the cloned renal anion channel ClC-K2 and likely reflect the basolateral Cl- conductances of the cells of these nephron segments.