Independent Cl Research Articles

Structural and functional insights into the lipid regulation of human anion exchanger 2

Anion exchanger 2 (AE2) is an electroneutral Na+-independent Cl-/HCO3- exchanger belongs to the SLC4 transporter family. The widely expressed AE2 participates in a variety of physiological processes, including transepithelial acid-base secretion and osteoclastogenesis. Both the transmembrane domains (TMDs) and the N-terminal cytoplasmic domain (NTD) are involved in regulation of AE2 activity. However, the regulatory mechanism remains unclear. Here, we report a 3.2 Å cryo-EM structure of the AE2 TMDs in complex with PIP2 and a 3.3 Å full-length mutant AE2 structure in the resting state without PIP2. We demonstrate that PIP2 at the TMD dimer interface is involved in the substrate exchange process. Mutation in the PIP2 binding site leads to the displacement of TM7 and further stabilizes the interaction between the TMD and the NTD. Reduced substrate transport activity and conformation similar to AE2 in acidic pH indicating the central contribution of PIP2 to the function of AE2.

Extracellular H+ Ions are a Novel Signal for Tyrosine Hydroxylase Activation in Catecholaminergic Cells.

Tyrosine hydroxylase catalyzes the rate-limiting step in the catecholamine biosynthetic pathway. Short-term TH activity is proposed to be regulated by the phosphorylation/dephosphorylation of regulatory domains Ser 40, 31, and/or 19 in response to membrane depolarization coupled increase in intracellular Ca2+. Here, we present in situ evidence to support that extracellular H+ ions ([H+]o) are an intracellular or extracellular Ca2+-independent novel signal for TH activation in catecholaminergic MN9D and PC12 cells. [H+]o-mediated TH activation is a short-term process coupled with a Na+-independent Cl-/HCO3- exchanger-mediated increase of intracellular hydrogen ions ([H+]i). While extracellular Ca2+ is not required for [H+]o-mediated TH activation, [H+]o does not increase the cytosolic Ca2+ levels in neuronal or non-neuronal cells in the presence or absence of extracellular Ca2+. Although [H+]o-mediated TH activation is associated with a significant increase in Ser 40 phosphorylation, major protein kinases proposed to be responsible for this process appear to be not involved. However, we have not been able to identify the protein kinase(s) involved in [H+]o-mediated phosphorylation of TH at present. Studies with a pan-phosphatase inhibitor, okadaic acid (OA), appear to indicate that the inhibition of phosphatase activities may not play a significant role in H+-mediated activation of TH. The relevance of these findings to the physiological TH activation mechanism and hypoxia, ischemia, and trauma-induced selective dopaminergic neural death is being discussed in this paper.

Translation, Validation, and Cultural Adaptation of CLEFT-Q© for use in Indonesia.

To translate and validate CLEFT-Q©, patient-reported outcome measure for patients with cleft lip and/or palate (CL and/or P), into Indonesian. CLEFT-Q© covers the domains of appearance, facial function, health-related quality of life and consists of scales describing outcomes after cleft surgery. The CLEFT-Q© instrument was translated according to the International Society of Pharmacoeconomics and Outcomes Research guidelines, including translation, cognitive debriefing, and field-testing. Dr. Cipto Mangunkusumo Hospital, Indonesia; independent CL and/or P support groups. Patients ages 8-29 with a history of repaired CL and/or P were grouped based on age. Those unable to complete the questionnaire independently were excluded. The primary objective was reliable translation of the CLEFT-Q® instrument. Each scale was assessed for its internal consistency (Cronbach's alpha) and validity (inter-item correlation), and sub-group analyses were performed based on age group. Forward and back translation revealed 25(13.3%) and 12(6.3%) of items were difficult to translate. Cognitive debriefing revealed 10(5.3%) items were difficult to understand, with the lowest reliability on the facial appearance scale (α=0.27). Other scales demonstrated acceptable to excellent reliability (α=0.53-0.68). Field testing revealed acceptable reliability and validity of the translation (α = 0.74-0.92; 69% ideal range of inter-item correlation). Sub-group analyses revealed patients in the <11y.o. and >18y.o. groups had the lowest scores on the "cleft lip scar" scale while those 11-18y.o. had the lowest scores on the "nostrils" scale. Iterative translation and cultural adaptation of CLEFT-Q© into Indonesian demonstrated reliability and validity of the tool, supported by acceptable to excellent internal consistency and ideal inter-item correlation.

Elevator transport mechanism in SLC4 transporters: Insights from new inward facing cryo-EM structures of AE1.

The SLC4 transporters are responsible for the transport of various ions, such as HCO3−, CO32−, Cl−, Na+, and NH3+H+, necessary for maintenance of pH, blood pressure and ion homeostasis in the body. Among them, the AE1 transporter protein (Anion Exchanger 1, Band 3, SLC4A1), a Na+-independent Cl−/HCO3− exchanger, has been extensively studied both from theoretical and experimental perspective, due to its peculiarly high rate of transport. An outward facing (OF) open structure of the human AE1 has been previously resolved and substrate binding sites in it have been identified both from computational, functional mutagenesis, and cryoEM studies. However, detailed understanding of the transport mechanism of AE1 and other members of the SLC4 family is hindered by lack of structures of other catalytically relevant states. In the present work we report cryoEM structures of dimers of bovine AE1 (bAE1), which feature inward facing (IF) open monomers. Moreover, mixed dimers where one monomer is in IF and the other - in OF state, were also resolved, indicating independent movement of monomers in the dimers. The new IF and OF states of bAE1 provide unambiguous structural evidence for elevator transport mechanism with a small vertical shift of the core domain with respect to the rigid gate domain. An unexpected elongation of transmembrane helix (TM) 11 and the accompanying reorganization of intracellular loop (IL) 5 from beta-hairpin into alpha-helical geometry is also observed in the IF state. Computational modelling demonstrates different anion dynamics at both sides of the lipid membrane. The small structural reorganization during the OF to IF transition, and the fast anion permeation into the IF and OF cavities of AE1 emerge as possible explanations of the observed high transport rate of this protein.

Genome-wide characterization of the Triplophysa dalaica slc4 gene family and expression profiles in response to salinity changes

BackgroundThe solute carrier 4 (SLC4) gene family is involved in a variety of physiological processes in organisms and is essential for maintaining acid-base balance in the body. The slc4 genes have been extensively studied in mammals, and they play important roles in intracellular and extracellular pH regulation and in the secretion and uptake of HCO3− and other ions (Na+ and Cl−) between transepithelial cells in different tissues. This study identified and characterized the entire slc4 gene family of Triplophysa dalaica.ResultsFifteen slc4 genes were identified in the whole genome of Triplophysa dalaica in this study, including five copies of Na+-independent Cl−/HCO3− transporters, eight members of Na+-dependent HCO3− transporters, and two genes coding Na+-coupled borate transporters. The chromosomal location information, isoelectric points, and molecular weights of the 15 slc4 genes were analyzed. The results for gene structure, domain analysis, and phylogenetic relationships of this gene family showed that the slc4 genes (except for slc4a9, which is missing in teleosts) are significantly expanded in teleosts compared to higher vertebrates. This phenomenon suggests that the slc4 gene family played an important role in the transition from aquatic to terrestrial animals. RT-PCR results showed that different slc4 genes showed diversified expression patterns in the tissues of T. dalaica. For osmotic pressure regulating organs, slc4a1b, slc4a4b, slc4a7, and slc4a11a were highly expressed in gills. In the kidney, slc4a1a, slc4a3, and slc4a10b were highly expressed, suggesting that the slc4 genes play a specific role in the salinity adaptation of T. dalaica. Our study has deciphered the biological roles of the slc4 genes in maintaining ionic and acid-base homeostasis in teleost fishes and provides a foundation for future exploration of the highly differentiated gene family in Triplophysa.ConclusionsThe results are relevant for the breeding of alkali-tolerant varieties in saline-alkali areas for aquaculture. Our findings have important implications for the adaptation process of freshwater species to saline-alkali water.

The stability of Cl-, Br-, and I-passivated Si(100)-(2 × 1) in ambient environments for atomically-precise pattern preservation

Atomic precision advanced manufacturing (APAM) leverages the highly reactive nature of Si dangling bonds relative to H- or Cl-passivated Si to selectively adsorb precursor molecules into lithographically defined areas with sub-nanometer resolution. Due to the high reactivity of dangling bonds, this process is confined to ultra-high vacuum (UHV) environments, which currently limits its commercialization and broad-based appeal. In this work, we explore the use of halogen adatoms to preserve APAM-derived lithographic patterns outside of UHV to enable facile transfer into real-world commercial processes. Specifically, we examine the stability of H-, Cl-, Br-, and I-passivated Si(100) in inert N2 and ambient environments. Characterization with scanning tunneling microscopy and x-ray photoelectron spectroscopy (XPS) confirmed that each of the fully passivated surfaces were resistant to oxidation in 1 atm of N2 for up to 44 h. Varying levels of surface degradation and contamination were observed upon exposure to the laboratory ambient environment. Characterization by ex situ XPS after ambient exposures ranging from 15 min to 8 h indicated the Br– and I–passivated Si surfaces were highly resistant to degradation, while Cl–passivated Si showed signs of oxidation within minutes of ambient exposure. As a proof-of-principle demonstration of pattern preservation, a H–passivated Si sample patterned and passivated with independent Cl, Br, I, and bare Si regions was shown to maintain its integrity in all but the bare Si region post-exposure to an N2 environment. The successful demonstration of the preservation of APAM patterns outside of UHV environments opens new possibilities for transporting atomically-precise devices outside of UHV for integrating with non-UHV processes, such as other chemistries and commercial semiconductor device processes.

Sulfur Dioxide Activates Cl-/HCO3 - Exchanger via Sulphenylating AE2 to Reduce Intracellular pH in Vascular Smooth Muscle Cells.

Sulfur dioxide (SO2) is a colorless and irritating gas. Recent studies indicate that SO2 acts as the gas signal molecule and inhibits vascular smooth muscle cell (VSMC) proliferation. Cell proliferation depends on intracellular pH (pHi). Transmembrane cystein mutation of Na+- independent Cl-/HCO3- exchanger (anion exchanger, AE) affects pHi. However, whether SO2 inhibits VSMC proliferation by reducing pHi is still unknown. Here, we investigated whether SO2 reduced pHi to inhibit the proliferation of VSMCs and explore its molecular mechanisms. Within a range of 50–200 μM, SO2 was found to lower the pHi in VSMCs. Concurrently, NH4Cl pre-perfusion showed that SO2 significantly activated AE, whereas the AE inhibitor 4,4′-diisothiocyanatostilbene- 2,20-disulfonic acid (DIDS) significantly attenuated the effect of SO2 on pHi in VSMCs. While 200 μM SO2 sulphenylated AE2, while dithiothreitol (DTT) blocked the sulphenylation of AE2 and subsequent AE activation by SO2, thereby restoring the pHi in VSMCs. Furthermore, DIDS pretreatment eliminated SO2-induced inhibition of PDGF-BB-stimulated VSMC proliferation. We report for the first time that SO2 inhibits VSMC proliferation in part by direct activation of the AE via posttranslational sulphenylation and induction of intracellular acidification.

Exploring the Transport Mechanism of the Human AE4 (SLC4A9) CL-/HCO3- Exchanger

The SLC4 family includes Na+-independent Cl-/HCO3- exchangers and Na+-coupled HCO3- transporters. SLC4 proteins are crucial for important physiological processes, including CO2 transport, intracellular and extracellular pH regulation and HCO3- transport in epithelia. The AE4 (SLC4A9) protein plays a role in NaCl reabsorption and Cl--dependent fluid secretion in distal nephron and salivary glands respectively; however, its transport mechanism remains controversial. It has been proposed that AE4 mediates Cl-/HCO3- exchange, Na+-HCO3- cotransport or Cl-/cation-HCO3- exchange suggesting that shares functional features with both the Cl-/HCO3- exchanger AE1(SLC4A1) and the Na+-HCO3- co-transporter NBCe1 (SLC4A4). Our sequence alignments show that AE1, NBCe1 and AE4 share high amino-acidic identity in the transmembrane domain. Functionally relevant residues in AE1 and NBCe1 are conserved in AE4, suggesting that the ion transport mechanism should be encoded by the same set of residues. We explored the transport mechanism of the human version of AE4 using molecular modeling, site-directed mutagenesis and functional assays. Our molecular simulations show that the proposed anion-binding site in AE1, between the helical ends of TM 3 and TM10, is also present in AE4. Three residues at this region have been postulated to be crucial for anion transport in AE1 and NBCe1. We mutated homologous D709, T448 and I758 in AE4 and found that only T448 is functionally important. Additional mutations of S754 and T756 in this region dońt show functional changes compared to WT AE4. These results suggest that the predicted ion-binding site in AE4 requires T448 to support the transport cycle but, in contrast to AE1 and NBCe1, residues at equivalent positions 709 and 758 are not important for function.

Versatility of NaCl transport mechanisms in the cortical collecting duct.

The cortical collecting duct (CCD) forms part of the aldosterone-sensitive distal nephron and plays an essential role in maintaining the NaCl balance and acid-base status. The CCD epithelium comprises principal cells as well as different types of intercalated cells. Until recently, transcellular Na+ transport was thought to be restricted to principal cells, whereas (acid-secreting) type A and (bicarbonate-secreting) type B intercalated cells were associated with the regulation of acid-base homeostasis. This review describes how this traditional view has been upended by several discoveries in the past decade. A series of studies has shown that type B intercalated cells can mediate electroneutral NaCl reabsorption by a mechanism involving Na+-dependent and Na+-independent Cl-/[Formula: see text] exchange, and that is energetically driven by basolateral vacuolar H+-ATPase pumps. Other research indicates that type A intercalated cells can mediate NaCl secretion, through a bumetanide-sensitive pathway that is energized by apical H+,K+-ATPase type 2 pumps operating as Na+/K+ exchangers. We also review recent findings on the contribution of the paracellular route to NaCl transport in the CCD. Last, we describe cross-talk processes, by which one CCD cell type impacts Na+/Cl- transport in another cell type. The mechanisms that have been identified to date demonstrate clearly the interdependence of NaCl and acid-base transport systems in the CCD. They also highlight the remarkable versatility of this nephron segment.

Structure and Function of SLC4 Family [Formula: see text] Transporters.

The solute carrier SLC4 family consists of 10 members, nine of which are transporters, including three Na+-independent Cl−/ exchangers AE1, AE2, and AE3, five Na+-coupled transporters NBCe1, NBCe2, NBCn1, NBCn2, and NDCBE, as well as “AE4” whose Na+-dependence remains controversial. The SLC4 transporters play critical roles in pH regulation and transepithelial movement of electrolytes with a broad range of demonstrated physiological relevances. Dysfunctions of these transporters are associated with a series of human diseases. During the past decades, tremendous amount of effort has been undertaken to investigate the topological organization of the SLC4 transporters in the plasma membrane. Based upon the proposed topology models, mutational and functional studies have identified important structural elements likely involved in the ion translocation by the SLC4 transporters. In the present article, we review the advances during the past decades in understanding the structure and function of the SLC4 transporters.

The role of pendrin in blood pressure regulation.

Pendrin is a Na(+)-independent Cl(-)/HCO3(-) exchanger found in the apical regions of type B and non-A, non-B intercalated cells within the aldosterone-sensitive region of the nephron, i.e., the distal convoluted tubule (DCT), the connecting tubule (CNT), and the cortical collecting duct (CCD). Type B intercalated cells mediate Cl(-) absorption and HCO3(-) secretion primarily through pendrin-mediated Cl(-)/HCO3(-) exchange. This exchanger is upregulated with angiotensin II administration and in models of metabolic alkalosis, such as following administration of aldosterone or NaHCO3. In the absence of pendrin-mediated HCO3(-) secretion, an enhanced alkalosis is observed following aldosterone or NaHCO3 administration. However, probably of more significance is the role of pendrin in the pressor response to aldosterone. Pendrin mediates Cl(-) absorption and modulates aldosterone-induced Na(+) absorption mediated by the epithelial Na channel (ENaC). Pendrin changes ENaC activity by changing both channel open probability (Po) and surface density (N), at least partly by altering luminal HCO3(-) and ATP concentration. Thus aldosterone and angiotensin II stimulate pendrin expression and function, which stimulates ENaC activity, thereby contributing to the pressor response of these hormones. However, pendrin may modulate blood pressure partly through its extrarenal effects. For example, pendrin is expressed in the adrenal medulla, where it modulates catecholamine release. The increase in catecholamine release observed with pendrin gene ablation likely contributes to the increment in vascular contractile force observed in the pendrin null mouse. This review summarizes the signaling mechanisms that regulate pendrin abundance and function as well as the contribution of pendrin to distal nephron function.

A novel mechanism for the anticonvulsant effect of furosemide in rat hippocampus in vitro

Though both in vivo and in vitro studies have demonstrated an anticonvulsant effect of the loop diuretic furosemide, the precise mechanism behind this effect is still debated. The current study investigates the effect of furosemide on Cs-induced epileptiform activity (Cs-FP) evoked in area CA1 of rat hippocampal slices in the presence of Cs+ (5mM) and ionotropic glutamatergic and GABAergic receptor antagonists. As this model diverges in several respects from other epilepsy models it can offer new insight into the mechanism behind the anticonvulsive effect of furosemide. The present study shows that furosemide suppresses the Cs-FP in a dose-dependent manner with a near complete block at concentrations≥1.25mM. Because furosemide targets several types of ion transporters we examined the effect of more selective antagonists. Bumetanide (20μM), which selectively inhibits the Na–K–2Cl co-transporter (NKCC1), had no significant effect on the Cs-FP. VU0240551 (10μM), a selective antagonist of the K–Cl co-transporter (KCC2), reduced the ictal-like phase by 51.73±8.5% without affecting the interictal-like phase of the Cs-FP. DIDS (50μM), a nonselective antagonist of Cl−/HCO3−-exchangers, Na+–HCO3−-cotransporters, chloride channels and KCC2, suppressed the ictal-like phase by 60.8±8.1% without affecting the interictal-like phase. At 500μM, DIDS completely suppressed the Cs-FP. Based on these results we propose that the anticonvulsant action of furosemide in the Cs+-model is exerted through blockade of the neuronal KCC2 and Na+-independent Cl−/HCO3−-exchanger (AE3) leading to stabilization of the activity-induced intracellular acidification in CA1 pyramidal neurons.

The role of pendrin in renal physiology.

Pendrin is a Na(+)-independent Cl(-)/HCO3(-) exchanger that localizes to type B and non-A, non-B intercalated cells, which are expressed within the aldosterone-sensitive region of the nephron, i.e., the distal convoluted tubule, the connecting tubule, and the cortical collecting duct. Type B cells mediate Cl(-) absorption and HCO3(-) secretion primarily through pendrin-mediated Cl(-)/HCO3(-) exchange. At least in some treatment models, pendrin acts in tandem with the Na(+)-dependent Cl(-)/HCO3(-) exchanger (NDCBE) encoded by Slc4a8 to mediate NaCl absorption. The pendrin-mediated Cl(-)/HCO3(-) exchange process is greatly upregulated in models of metabolic alkalosis, such as following aldosterone administration or dietary NaHCO3 loading. It is also upregulated by angiotensin II. In the absence of pendrin [Slc26a4 (-/-) or pendrin null mice], aldosterone-stimulated NaCl absorption is reduced, which lowers the blood pressure response to aldosterone and enhances the alkalosis that follows the administration of this steroid hormone. Pendrin modulates aldosterone-induced Na(+) absorption by changing ENaC abundance and function through a kidney-specific mechanism that does not involve changes in the concentration of a circulating hormone. Instead, pendrin changes ENaC abundance and function at least in part by altering luminal HCO3(-) and ATP concentrations. Thus, aldosterone and angiotensin II also stimulate pendrin expression and function, which likely contributes to the pressor response of these hormones. This review summarizes the contribution of the Cl(-)/HCO3(-) exchanger pendrin in distal nephron function.

Effects of Increasing Tungsten on Structural, Elastic and Optical Properties of xWO3–(40−x)Ag2O–60Te2O Glass System

Ternary tellurite glasses with composition of xWO3(40−x)Ag2O–60TeO2 (x = 0–40 mol%) have been prepared by melt-quenching method. Elastic and optical properties of the glass system were obtained by ultrasonic velocity measurements and UV–vis spectroscopy, respectively, while structural investigation was carried out by using Raman spectroscopy. The longitudinal and shear velocities, vL and vs showed large increase at x from 0 to 20 mol% before decrease with further addition of WO3. Independent longitudinal modulus CL and shear modulus μ bulk modulus Ke Young's modulus Y and Debye temperature θD showed similar behaviors to both velocities. The large increase of the elastic moduli at x from 0 to 20 mol% is suggested to be due to the increase in WO6 octahedral unit structure indicating the increase of bridging oxygen (BO) and formation of stronger Te–O–W bonds compared to Te–O–Te bonds. On the other hand, for x > 20 mol%, the decrease in the elastic moduli was due to the increase of non-bridging oxygen (NBO) as a result of formation of WO4 tetrahedral via breaking Te–O–W network. Further analysis by using bulk compression and ring deformation models showed a slight decrease in the ratio of ideal bulk modulus Kbc to the experimental bulk modulus Ke and average atomic ring size, l for x 20 mol%. Our analysis also indicates that limited ring deformation took place and the main compression mechanism in this glass system was mainly ideal isotropic compression. On the other hand, optical band gap Eopt showed small variation for x = 0–20 mol% but decreased upon higher WO3 content while refractive index n showed the opposite trend. This optical behavior is suggested to be related to the changes in cross link density and NBO concentration in the glass system.

Pendrin localizes to the adrenal medulla where it modulates catecholamine release (701.1)

Pendrin is an aldosterone‐sensitive, Na+‐independent Cl‐/HCO3‐ exchanger expressed in intercalated cells within the renal cortex where it modulates blood pressure. Since pendrin gene ablation stimulates the release of renin, but not aldosterone, we hypothesized that pendrin is expressed in the adrenal gland and modulates adrenal function. Thus, we examined rat and mouse adrenal pendrin mRNA and protein abundance by PCR, immunoblot and immunohistochemistry and examined adrenal responses in wild type and pendrin null mice. Pendrin protein was detected in adrenal lysates from wild type, but not pendrin null mice. In both mice and rats, we observed pendrin mRNA and protein in the adrenal medulla but not in the adrenal cortex. Since the adrenal medulla produces catecholamines, further experiments examined plasma epinephrine responses to 5 and 20 min of immobilization stress in wild type and pendrin null mice. Basal epinephrine concentration was similar in wild type and pendrin null mice. Immobilization stress increased epinephrine in both groups, but responses were ~50% higher in pendrin null vs wild type after either 5 or 20 min of immobilization stress (20 min: KO, 1562 ± 263, n=4, vs WT, 1041 ± 129 pg/ml, n=6, P &lt; 0.05). We conclude that pendrin is expressed in the adrenal medulla where it may blunt stress‐induced epinephrine release.Grant Funding Source: Supported by NIH

Anion exchanger 2 is critical for CD8+ T cells to maintain pHi homeostasis and modulate immune responses

Mitogenic stimulation of lymphocytes involves alkalinization of intracellular pH (pHi ). Subsequent pHi regulation may involve HCO3 (-) extrusion through Cl(-) /HCO3 (-) exchangers and/or Na(+) -HCO3 (-) co-transporters with acid-loading capability. Abnormalities in these mechanisms could result in immune dysfunctions, as suggested by the CD8(+) T-cell expansion encountered in mice lacking Ae2 (a widely expressed acid loader with electroneutral and Na(+) -independent Cl(-) /HCO3 (-) anion-exchange activity). Here we report that CD8(+) T cells but not CD4(+) T cells or other lymphocyte populations, are crucially dependent on Ae2 for pHi regulation. While total lymphocytes (including isolated CD4(+) T cells) exhibit Ae1 expression and Na(+) -HCO3 (-) co-transport with acidifying potential, CD8(+) T cells lack these acid-loading mechanisms. In Ae2-KO mice, CD4(+) but not CD8(+) T cells upregulate these potential Ae2 surrogates. As a consequence, Ae2-KO CD8(+) T cells exhibit alkalinized pHi , and dramatically increase their pHi upon CD3 stimulation. Moreover, stimulated Ae2-deficient CD8(+) T cells show enhanced intracellular production of IL-2 and membrane expression of its receptor IL-2Rα, together with increased cell proliferation and activation. These findings demonstrate that CD8(+) T cells are critically dependent on Ae2 for pHi homeostasis and tuning of cell proliferation and activation. Ae2 thus constitutes a novel target to modulate CD8(+) T-cell responses.

Cortical distal nephron Cl−transport in volume homeostasis and blood pressure regulation

Renal intercalated cells mediate the secretion or absorption of Cl(-) and OH(-)/H(+) equivalents in the connecting segment (CNT) and cortical collecting duct (CCD). In so doing, they regulate acid-base balance, vascular volume, and blood pressure. Cl(-) absorption is either electrogenic and amiloride-sensitive or electroneutral and thiazide-sensitive. However, which Cl(-) transporter(s) are targeted by these diuretics is debated. While epithelial Na(+) channel (ENaC) does not transport Cl(-), it modulates Cl(-) transport probably by generating a lumen-negative voltage, which drives Cl(-) flux across tight junctions. In addition, recent evidence indicates that ENaC inhibition increases electrogenic Cl(-) secretion via a type A intercalated cells. During ENaC blockade, Cl(-) is taken up across the basolateral membrane through the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) and then secreted across the apical membrane through a conductive pathway (a Cl(-) channel or an electrogenic exchanger). The mechanism of this apical Cl(-) secretion is unresolved. In contrast, thiazide diuretics inhibit electroneutral Cl(-) absorption mediated by a Na(+)-dependent Cl(-)/HCO3(-) exchanger. The relative contribution of the thiazide and the amiloride-sensitive components of Cl(-) absorption varies between studies and probably depends on the treatment model employed. Cl(-) absorption increases markedly with angiotensin and aldosterone administration, largely by upregulating the Na(+)-independent Cl(-)/HCO3(-) exchanger pendrin. In the absence of pendrin [Slc26a4((-/-)) or pendrin null mice], aldosterone-stimulated Cl(-) absorption is significantly reduced, which attenuates the pressor response to this steroid hormone. Pendrin also modulates aldosterone-induced changes in ENaC abundance and function through a kidney-specific mechanism that does not involve changes in the concentration of a circulating hormone. Instead, pendrin changes ENaC abundance and function, at least in part, by altering luminal HCO3(-). This review summarizes mechanisms of Cl(-) transport in CNT and CCD and how these transporters contribute to the regulation of extracellular volume and blood pressure.

Relative growth, morphological sexual maturity, and size of Macrobrachium amazonicum (Heller 1862) (Crustacea, Decapoda, Palaemonidae) in a population with an entirely freshwater life cycle

The objective of this study was to estimate the size of morphological sexual maturity based on the study of relative growth, to determine the maximum size of individuals, and to determine if there are different morphotypes of males in a population of Macrobrachium amazonicum with an entirely freshwater life cycle. Collections were made monthly, with the use of a net, from September 2006 through August 2007. In each individual, the following structures were measured: carapace length (CL, in mm), width of the second pleuron (PlL, mm), length of the carpus (CaL, mm), and length of the propodus (PrL, mm). Relative growth was analyzed by observing the change in growth patterns of certain parts of the body in relation to the independent variable CL. The maximum sizes found were 8.5 and 11.4 mm CL for males and females, respectively. The morphometric variables: length of the carpus (CL × CaL) for males, and width of the second pleuron (CL × PlL) for females gave the best estimates for the size at maturation, which was 4.26 mm CL for males and 5.39 mm CL for females. The growth pattern in the different stages and the beginning of differential growth seemed to be closely related to reproductive aspects. No indices were found that separated the males into four different morphotypes, as proposed in the literature for coastal or artificially farmed populations. Only the male morphotype termed translucent claw was found in this population. The different morphological patterns in different regions are probably explained by ecological differences in the environments inhabited by these groups, principally in the availability of nutrients and the salinity in which the larvae develop.

6-Amino-4-(3-iodoanilino)-2-methylpyrimidin-1-ium chloride

In the cation of the title salt, C11H12IN4 +·Cl−, the two aromatic rings are oriented to each other at 9.3 (2)°. In the crystal, the two independent Cl− anions lie on twofold rotation axes. N—H⋯Cl hydrogen bonds between the cations and anions generate a supra­molecular layer parallel to (010).

N,N'-Bis(2-aza-niumylbenz-yl)ethane-1,2-diaminium tetra-chloride.

The title compound, C16H26N4 4+·4Cl−, is based on a fully protonated tetra­amine. In the cation, both benzene rings are connected by an all-trans chain, and the rings are almost parallel, with an angle between the mean planes of 8.34 (12)°. The benzene rings are arranged in such a way that the NH3 + substituents are oriented cis with respect to the central chain. This arrangement is a consequence of multiple N—H⋯Cl hydrogen bonds, involving all N—H groups in the cation and the four independent Cl− anions. These contacts have strengths ranging from weak to strong (based on H⋯Cl separations), and generate a complex three-dimensional crystal structure with no preferential crystallographic orientation for the contacts.