The amperometric titration of plasma chloride and urine chloride

It has been shown that the method of Laitinen, Jennings, and Parks for the amperometric titration of chloride can be easily adapted to analyses of plasma (serum) and urine chlorides. For the procedure 1.0-ml. samples are diluted so that the mixture being titrated is 50% in acetone and 0.8 N in nitric acid. Silver nitrate, 0.0100 N, is used as the titrant, and the rotating platinum electrode is used as the indicator electrode. The method is simple, rapid, and as accurate as existing methods.When 0.1-ml. samples are analyzed, the accuracy is decreased a little over that obtained when 1.0-ml. samples are used.The method is not satisfactory for the analysis of chloride in the presence of whole blood or muscle tissue.     

Bead-like passage of chloride ions through ClC chloride channels

The ClC chloride channels control the ionic composition of the cytoplasm and the volume of cells, and regulate electrical excitability. Recently, it has been proposed that prokaryotic ClC channels are H+-Cl- exchange transporter. Although X-ray and molecular dynamics (MD) studies of bacterial ClC channels have investigated the filter open-close and ion permeation mechanism of channels, details have remained unclear. We performed MD simulations of ClC channels involving H+, Na+, K+, or H3O+ in the intracellular region to elucidate the open-close mechanism, and to clarify the role of H+ ion an H+-Cl- exchange transporter. Our simulations revealed that H+ and Na+ caused channel opening and the passage of Cl- ions. Na+ induced a bead-like string of Cl- -Na+-Cl--Na+-Cl- ions to form and permeate through ClC channels to the intracellular side with the widening of the channel pathway.     

Determination of chloride procedure based upon diffusion of hydrogen chloride

We describe a simple, inexpensive sample preparation method that involves the isolation of chloride as hydrogen chloride from serum and urine prior to chloride analysis with the chloride ion-selective electrode. Chloride analyses of clinical chemistry standards with the present method were found to be in good agreement with analyses reported by the manufacturer. Reliability of the method is also evident by complete recovery of chloride added to serum and urine, minimal day-to-day variation of analyses, and a coefficient of variation that generally is less than 2%. An evaluation of factors influencing the procedure is also reported. The usefulness of the chloride ion-selective electrode to determine chloride in serum or urine is greatly enhanced by the sample preparation method described since matrix interference by other sample components is removed prior to analysis.     

Trimethyltin chloride induced chloride secretion across rat distal colon

TMT (trimethyltin chloride), an organotin, is ubiquitous in the environment. The consumption of contaminated food may cause exposure of the human diet to this toxic compound. The present study was to investigate the effects of TMT on the regulation of ion transport across the rat distal colon. The rat colonic mucosa was mounted in Ussing chambers. The effects of TMT were assessed using the I_sc (short‐circuit current). Both apical and basolateral TMT induced, dose‐dependently, an increase in I_sc, which was due to a stimulation of Cl^? secretion as measured using ion substitution experiments and pharmacological manoeuvres. The secretion was also inhibited by several K⁺ channel blockers administrated at the basolateral side. When the apical side was permeabilized by nystatin, the TMT‐induced K⁺ conductance was effectively blocked by tetrapentylammonium, a Ca²⁺‐sensitive K⁺ channel blocker. The response of TMT was sensitive to the basolateral Ca²⁺ and the intracellular Ca²⁺ store, which could be disclosed by applying the inhibitors of ryanodine receptors and inositol 1,4,5‐trisphosphate receptors. In conclusion, TMT led to Cl^? secretion, which was essentially regulated by basolateral Ca²⁺‐sensitive K⁺ channels. These results suggest the importance of K⁺ channels in the toxicity hazard of TMT.     

Structural insights into chloride and proton-mediated gating of CLC chloride channels

CLC Cl(-) channels fulfill numerous physiological functions as demonstrated by their involvement in several human genetic diseases. They have an unusual homodimeric architecture in which each subunit forms an individual pore whose open probability is regulated by various physicochemical factors, including voltage, Cl(-) concentration, and pH. The voltage dependence of Torpedo channel CLC-0 is derived probably indirectly from the translocation of a Cl(-) ion through the pore during the opening step. Recent structure determinations of bacterial CLC homologues marked a breakthrough for the structure-function analysis of CLC channels. The structures revealed a complex fold with 18 alpha-helices and two Cl(-) ions per subunit bound in the center of the protein. The side chain of a highly conserved glutamate residue that resides in the putative permeation pathway appears to be a major component of the channel gate. First studies have begun to exploit the bacterial structures as guides for a rational structure-function analysis. These studies confirm that the overall structure seems to be conserved from bacteria to humans. A full understanding of the mechanisms of gating of eukaryotic CLC channels is, however, still lacking.     

Contribution of mucosal chloride to chloride in toad bladder epithelial cells

Summary Epithelial cells were scraped from the bladders of toads of the speciesBufo marinus obtained from the Dominican Republic. These epithelial cells exchanged their chloride virtually completely with³⁶Cl in the medium within 60 min. Of this chloride, about 93% came from the serosal medium. The approximately 20 mmole/kg dry wt of chloride which equilibrates with³⁶Cl in the mucosal medium was still present when choline replaced sodium in the medium in the presence of amiloride (10^–4 M) and was almost all readily removed by rapid washing of the mucosal surface immediately prior to analysis. These observations suggest that little chloride of mucosal origin is truly intracellular. This conclusion is supported by the fact that after vasopressin the increased cellular chloride was not of mucosal origin.     

ClC-3 chloride channels facilitate endosomal acidification and chloride accumulation

We investigated the involvement of ClC-3 chloride channels in endosomal acidification by measurement of endosomal pH and chloride concentration [Cl-] in control versus ClC-3-deficient hepatocytes and in control versus ClC-3-transfected Chinese hamster ovary cells. Endosomes were labeled with pH or [Cl-]-sensing fluorescent transferrin (Tf), which targets to early/recycling endosomes, or alpha2-macroglobulin (alpha2M), which targets to late endosomes. In pulse label-chase experiments, [Cl-] was 19 mM just after internalization in alpha2M-labeled endosomes in primary cultures of hepatocytes from wild-type mice, increasing to 58 mM over 45 min, whereas pH decreased from 7.1 to 5.4. Endosomal acidification and [Cl-] accumulation were significantly impaired in hepatocytes from ClC-3 knock-out mice, with [Cl-] increasing from 16 to 43 mM and pH decreasing from 7.1 to 6.0. Acidification and Cl- accumulation were blocked by bafilomycin. In Tf-labeled endosomes, [Cl-] was 46 mM in wild-type versus 35 mM in ClC-3-deficient hepatocytes at 15 min after internalization, with corresponding pH of 6.1 versus 6.5. Approximately 4-fold increased Cl- conductance was found in alpha2M-labeled endosomes isolated from hepatocytes of wild-type versus ClC-3 null mice. In contrast, Golgi acidification was not impaired in ClC-3-deficient hepatocytes. In transfected Chinese hamster ovary cells expressing ClC-3A, endosomal acidification and [Cl-] accumulation were enhanced. [Cl-] in alpha2M-labeled endosomes was 42 mM (control) versus 53 mM (ClC-3A) at 45 min, with corresponding pH 5.8 versus 5.2; [Cl-] in Tf-labeled endosomes at 15 min was 37 mM (control) versus 49 mM (ClC-3A) with pH 6.3 versus 5.9. Our results provide direct evidence for involvement of ClC-3 in endosomal acidification by Cl- shunting of the interior-positive membrane potential created by the vacuolar H+ pump.     

Diffusion of lysozyme chloride in water and aqueous potassium chloride solutions.

The diffusion of lysozyme chloride in aqueous solution has been studied at 25 degrees C using the Goüy interferometric technique. The concentration dependence of the diffusion coefficient in water has been measured over the concentration range 1.1599-9.1556 gcm-3 and the results suggest a value of D 25, w at infinite dilution of 5.838 x 10(-6) cm2s-1. The variation in diffusion coefficient with ionic strength has also been considered by following the diffusion of 0.45% lysozyme chloride in a series of potassium chloride solutions. The value of D in 0.15 M KCl has been found to be approximately one quarter of that in water alone an the diffusion coefficient has been shown to increase markedly as the KCl concentration is reduced below 0.05 M. Interpretation of these observations involves consideration of solution electrostatic effects.     

ClC chloride channels

Chloride-conducting ion channels of the ClC family are emerging as critical contributors to a host of biological processes. These polytopic membrane proteins form aqueous pathways through which anions are selectively allowed to pass down their concentration gradients. The ClCs are found in nearly all organisms, with members in every mammalian tissue, yet relatively little is known about their mechanism or regulation. It is clear, however, that they are fundamentally different in molecular construction and mechanism from the well-known potassium-, sodium-, and calcium-selective channels. The medical importance of ClC channels - four inherited diseases have been blamed on familial ClC dysfunction to date - highlights their diverse physiological functions and provides strong motivation for further study.     

The sodium and chloride dependence of chloride secretion by the opercular epithelium

The effects of ion substitutions on the Cl- secretion rate and tissue conductance of isolated short-circuited opercular epithelia from sea-water-adapted Fundulus heteroclitus were investigated. Serosal Na+ substitution had the same effect on the Cl- secretion rate that serosal Cl- substitution had on the active component of the Cl- efflux. This similarity indicated a 1:1 Na-Cl requirement for active Cl- secretion across this epithelium, which supports the proposal of a coupled NaCl uptake mechanism at the serosal membrane of Cl- secretory epithelia. Mucosal Na+ and Cl- substitutions appeared to inhibit completely the active Cl- secretory flux. The reductions in the tissue conductance with mucosal ion substitutions suggested that this effect can be attributed to a blocking of the apical membrane Cl- conductance. These mucosal ion effects suggested a possible direct regulatory influence of the external salinity on the Cl- secretion rate and tissue conductance, which provide alternative explanations for observations with the teleost gill epithelium.     

Theoretical mechanism of the formation of cholesteryl chloride from cholesterol and thionyl chloride

This work describes a theoretical approach to the substitution reaction mechanism involving the conversion of cholesterol to cholesteryl chloride. Two chlorosulfite ester molecules were formed as intermediates. An iso-steroid was found as the transition state. The final product was cholesteryl chloride and the side products were HCl and SO₂. Calculations were carried out at high level Hartree–Fock theory, using the 6–31G* basis set. From the electronic structure of the reactants, the most important physicochemical properties involved in the reaction pathway were used. Thus, to determine the participation of each molecule and to explain the mechanism of reaction; the total energy, HOMO and LUMO, atomic orbital contribution to frontier orbitals formation, electrostatic potentials, atomic charges, hardness and dipole moment were used. Characterization of intermediates and transition state was supported by their respective energy minima, fundamental frequencies and equilibrium geometry.Figure Synopsis of the reaction pathway. The reaction starts when the lone pair of the Ch oxygen interacts with the sulfur atom, releasing a chloride ion. As a result, the first intermediate is formed. Next, in the first intermediate the nucleophilic chloride ion bonds the electrophilic hydrogen atom, releasing HCl and yielding the second intermediate. In the second intermediate, the electrophilic H-atom from HCl bonds with the lone pair of the Cl atom adjacent to the sulfur atom, restoring HCl. Concurrently, SO₂ is liberated and causes the formation of the C3-C5 partial bond and breaking of the C5-C6 -bond leading to the transition state. In the transition state, the electrophilic H from HCl bonds with the Cl lone pair at C6-Cl, forming HCl again and leaving the C6 atom electron-deficient, which restores the C5-C6 -bond and breaks the C3-C5 partial bond. Finally, the electrophilic C3 atom and the nucleophilic Cl atom form a bond, yielding cholesteryl chloride. HCl and SO₂ are also formed as side products. The arrows show the rearrangement of electrons.     

Impact of benzalkonium chloride,benzethonium chloride and chloroxylenol on bacterial antimicrobial resistance

This review examined 3655 articles on benzalkonium chloride (BKC), benzethonium chloride (BZT) and chloroxylenol (CHO) aiming to understand their impact on antimicrobial resistance. Following the application of inclusion/exclusion criteria, only 230 articles were retained for analysis; 212 concerned BKC, with only 18 for CHO and BZT. Seventy-eight percent of studies used MIC to measure BKC efficacy. Very few studies defined the term ‘resistance’ and 85% of studies defined ‘resistance’ as <10-fold increase (40% as low as 2-fold) in MIC. Only a few in vitro studies reported on formulated products and when they did, products performed better. In vitro studies looking at the impact of BKC exposure on bacterial resistance used either a stepwise training protocol or exposure to constant BKC concentrations. In these, BKC exposure resulted in elevated MIC or/and MBC, often associated with efflux, and at time, a change in antibiotic susceptibility profile. The clinical relevance of these findings was, however, neither reported nor addressed. Of note, several studies reported that bacterial strains with an elevated MIC or MBC remained susceptible to the in-use BKC concentration. BKC exposure was shown to reduce bacterial diversity in complex microbial microcosms, although the clinical significance of such a change has not been established. The impact of BKC exposure on the dissemination of resistant genes (notably efflux) remains speculative, although it manifests that clinical, veterinary and food isolates with elevated BKC MIC carried multiple efflux pump genes. The correlation between BKC usage and gene carriage, maintenance and dissemination has also not been established. The lack of clinical interpretation and significance in these studies does not allow to establish with certainty the role of BKC on AMR in practice. The limited literature and BZT and CHO do not allow to conclude that these will impact negatively on emerging bacterial resistance in practice.     

细胞外氯离子浓度对大鼠ClC-1通道去激活动力学特性的影响

为探讨C1C－1通道的门控机制,实验应用爪蟾母细胞异源性表达大鼠野生型C1C－1（WT RC1C-1)通道基因,并使用双电极电压钳法记录通道电流。通过改变细胞外氯离子浓度,采用双指数拟合的方法分析通道去激活电流,对其去激活门控动力学特性进行了研究。结果表明,降低细胞外氯离子浓度可增加快速去激活电流成分,减少慢速去激活成分;同时,慢速去激活和快速去激活电流的时间常数都显著减小,说明细胞外氯离子浓度的改变可影响通道去激活动力学参数,从而改变通道的门控过程。     

Electrostatic control and chloride regulation of the fast gating of ClC-0 chloride channels

The opening and closing of chloride (Cl-) channels in the ClC family are thought to tightly couple to ion permeation through the channel pore. In the prototype channel of the family, the ClC-0 channel from the Torpedo electric organ, the opening-closing of the pore in the millisecond time range known as "fast gating" is regulated by both external and internal Cl- ions. Although the external Cl- effect on the fast-gate opening has been extensively studied at a quantitative level, the internal Cl- regulation remains to be characterized. In this study, we examine the internal Cl- effects and the electrostatic controls of the fast-gating mechanism. While having little effect on the opening rate, raising [Cl-]i reduces the closing rate (or increases the open time) of the fast gate, with an apparent affinity of >1 M, a value very different from the one observed in the external Cl- regulation on the opening rate. Mutating charged residues in the pore also changes the fast-gating properties-the effects are more prominent on the closing rate than on the opening rate, a phenomenon similar to the effect of [Cl-]i on the fast gating. Thus, the alteration of fast-gate closing by charge mutations may come from a combination of two effects: a direct electrostatic interaction between the manipulated charge and the negatively charged glutamate gate and a repulsive force on the gate mediated by the permeant ion. Likewise, the regulations of internal Cl- on the fast gating may also be due to the competition of Cl- with the glutamate gate as well as the overall more negative potential brought to the pore by the binding of Cl-. In contrast, the opening rate of the fast gate is only minimally affected by manipulations of [Cl-]i and charges in the inner pore region. The very different nature of external and internal Cl- regulations on the fast gating thus may suggest that the opening and the closing of the fast gate are not microscopically reversible processes, but form a nonequilibrium cycle in the ClC-0 fast-gating mechanism.