RESUMO

Slc4a genes encode various types of transporters, including Na+-HCO3- cotransporters, Cl-/HCO3- exchangers, or Na+-driven Cl-/HCO3- exchangers. Previous research has revealed that Slc4a9 (Ae4) functions as a Cl-/HCO3- exchanger, which can be driven by either Na+ or K+, prompting investigation into whether other Slc4a members facilitate cation-dependent anion transport. In the present study, we show that either Na+ or K+ drive Cl-/HCO3- exchanger activity in cells overexpressing Slc4a8 or Slc4a10. Further characterization of cation-driven Cl-/HCO3- exchange demonstrated that Slc4a8 and Slc4a10 also mediate Cl- and HCO3--dependent K+ transport. Full-atom molecular dynamics simulation on the recently solved structure of Slc4a8 supports the coordination of K+ at the Na+ binding site in S1. Sequence analysis shows that the critical residues coordinating monovalent cations are conserved among mouse Slc4a8 and Slc4a10 proteins. Together, our results suggest that Slc4a8 and Slc4a10 might transport K+ in the same direction as HCO3- ions in a similar fashion to that described for Na+ transport in the rat Slc4a8 structure.

Assuntos

Potássio , Simportadores de Sódio-Bicarbonato , Animais , Camundongos , Bicarbonatos/metabolismo , Sítios de Ligação , Antiportadores de Cloreto-Bicarbonato/metabolismo , Antiportadores de Cloreto-Bicarbonato/genética , Cloretos/metabolismo , Transporte de Íons , Simulação de Dinâmica Molecular , Potássio/metabolismo , Sódio/metabolismo , Simportadores de Sódio-Bicarbonato/metabolismo , Simportadores de Sódio-Bicarbonato/genética

RESUMO

The key role of CFTR in secretory epithelia has been extensively documented. Additionally, CFTR plays a significant role in ion absorption in exocrine glands, including salivary and sweat glands. Most of the knowledge about CFTR expression comes from animal models such as the mouse or the rat, but there is limited information about CFTR expression in human tissues. In the present study, we assessed the expression of CFTR in human submandibular and parotid glands. Consistent with findings in rodent salivary glands, our immunolocalization studies show that CFTR is expressed in duct cells. However, CFTR expression in human salivary glands differs from that in rodents, as immunolocalization and single-cell RNA sequencing analysis from a previous study performed in the human parotid gland revealed the presence of CFTR protein and transcripts within a distinct cell cluster. Based on cell marker expression, this cluster corresponds to acinar cells. To obtain functional evidence supporting CFTR expression, we isolated human parotid acinar cells through collagenase digestion. Acinar cells displayed an anion conductance that was activated in response to cAMP-increasing agents and was effectively blocked by CFTRInh172, a known CFTR blocker. This study provides novel evidence of CFTR expression within acinar cells of human salivary glands. This finding challenges the established model positioning CFTR exclusively in duct cells from exocrine glands.NEW & NOTEWORTHY This study addresses the uncertainty about the impact of CFTR on human salivary gland function. We found CFTR transcripts in a subset of duct cells known as ionocytes, as well as in acinar cells. Isolated human parotid acinar cells exhibited Cl- conductance consistent with CFTR activity. This marks the first documented evidence of functional CFTR expression in human salivary gland acinar cells.

Assuntos

Células Acinares , Regulador de Condutância Transmembrana em Fibrose Cística , Humanos , Ratos , Camundongos , Animais , Regulador de Condutância Transmembrana em Fibrose Cística/genética , Regulador de Condutância Transmembrana em Fibrose Cística/metabolismo , Glândulas Salivares/metabolismo , Glândula Submandibular/metabolismo , Glândula Parótida/metabolismo

RESUMO

Infusions of Valeriana pilosa are commonly used in Peruvian folk medicine for treating gastrointestinal disorders. This study aimed to investigate the spasmolytic and antispasmodic effects of Valeriana pilosa essential oil (VPEO) on rat ileum. The basal tone of ileal sections decreased in response to accumulative concentrations of VPEO. Moreover, ileal sections precontracted with acetylcholine (ACh), potassium chloride (KCl), or barium chloride (BaCl2) were relaxed in response to VPEO by a mechanism that depended on atropine, hyoscine butylbromide, solifenacin, and verapamil, but not glibenclamide. The results showed that VPEO produced a relaxant effect by inhibiting muscarinic receptors and blocking calcium channels, with no apparent effect on the opening of potassium channels. In addition, molecular docking was employed to evaluate VPEO constituents that could inhibit intestinal contractile activity. The study showed that α-cubebene, ß-patchoulene, ß-bourbonene, ß-caryophyllene, α-guaiene, γ-muurolene, valencene, eremophyllene, and δ-cadinene displayed the highest docking scores on muscarinic acetylcholine receptors and voltage-gated calcium channels, which may antagonize M2 and/or M3 muscarinic acetylcholine receptors and block voltage-gated calcium channels. In summary, VPEO has both spasmolytic and antispasmodic effects. It may block muscarinic receptors and calcium channels, thus providing a scientific basis for its traditional use for gastrointestinal disorders.

RESUMO

Two pore domain potassium channels (K2P) are strongly expressed in the nervous system (CNS), where they play a central role in excitability. These channels give rise to background K+ currents, also known as IKSO (standing-outward potassium current). We detected the expression in primary cultured cerebellar granule neurons (CGNs) of TWIK-1 (K2P1), TASK-1 (K2P3), TASK-3 (K2P9), and TRESK (K2P18) channels by immunocytochemistry and their association with lipid rafts using the specific lipids raft markers flotillin-2 and caveolin-1. At the functional level, methyl-ß-cyclodextrin (MßCD, 5 mM) reduced IKSO currents by ~40% in CGN cells. To dissect out this effect, we heterologously expressed the human TWIK-1, TASK-1, TASK-3, and TRESK channels in HEK-293 cells. MßCD directly blocked TASK-1 and TASK-3 channels and the covalently concatenated heterodimer TASK-1/TASK-3 currents. Conversely, MßCD did not affect TWIK-1- and TRESK-mediated K+ currents. On the other hand, the cholesterol-depleting agent filipin III did not affect TASK-1/TASK-3 channels. Together, the results suggest that neuronal background K+ channels are associated to lipid raft environments whilst the functional activity is independent of the cholesterol membrane organization.

RESUMO

Senecio nutans Sch. Bip. and its constituents are reported to have antihypertensive effects. We isolated metabolite−1, a natural compound from S. nutans (4-hydroxy-3-(isopenten-2-yl)-acetophenone), and synthesized novel oxime − 1 (4-hydroxy-3-(isopenten-2-yl)-acetophenoxime) to evaluate their effect on vascular reactivity. Compounds were purified (metabolite−1) or synthetized (oxime−1) and characterized using IR and NMR spectroscopy and Heteronuclear Multiple Quantum Coherence (HMQC). Using pharmacological agents such as phenylephrine (PE) and KCl (enhancing contraction), acetylcholine (ACh), L-NAME (nitric oxide (NO) and endothelial function), Bay K8644-induced CaV1.2 channel (calcium channel modulator), and isolated aortic rings in an organ bath setup, the possible mechanisms of vascular action were determined. Pre-incubation of aortic rings with 10−5 M oxime−1 significantly (p < 0.001) decreased the contractile response to 30 mM KCl. EC50 to KCl significantly (p < 0.01) increased in the presence of oxime−1 (37.72 ± 2.10 mM) compared to that obtained under control conditions (22.37 ± 1.40 mM). Oxime−1 significantly reduced (p < 0.001) the contractile response to different concentrations of PE (10−7 to 10−5 M) by a mechanism that decreases Cav1.2-mediated Ca2+ influx from the extracellular space and reduces Ca2+ release from intracellular stores. At a submaximal concentration (10−5 M), oxime−1 caused a significant relaxation in rat aorta even without vascular endothelium or after pre-incubate the tissue with L-NAME. Oxime−1 decreases the contractile response to PE by blunting the release of Ca2+ from intracellular stores and blocking of Ca2+ influx by channels. Metabolite−1 reduces the contractile response to KCl, apparently by reducing the plasma membrane depolarization and Ca2+ influx from the extracellular space. These acetophenone derivates from S. nutans (metabolite−1 and oxime−1) cause vasorelaxation through pathways involving an increase of the endothelial NO generation or a higher bioavailability, further highlighting that structural modification of naturally occurring metabolites can enhance their intended pharmacological functions.

Assuntos

Produtos Biológicos , Senécio , Acetofenonas/farmacologia , Animais , Aorta Torácica , Produtos Biológicos/farmacologia , Endotélio Vascular/metabolismo , NG-Nitroarginina Metil Éster/farmacologia , Óxido Nítrico/metabolismo , Oximas/farmacologia , Fenilefrina/farmacologia , Ratos , Vasodilatadores/química , Vasodilatadores/farmacologia

RESUMO

In mammals, the daily variation in the ecology of the intestinal microbiota is tightly coupled to the circadian rhythm of the host. On the other hand, a close correlation between increased body weight and light pollution at night has been reported in humans and animal models. However, the mechanisms underlying such weight gain in response to light contamination at night remain elusive. In the present study, we tested the hypothesis that dim light pollution at night alters the colonic microbiota of mice, which could correlate with weight gain in the animals. By developing an experimental protocol using a mouse model that mimics light contamination at night in urban residences (dLAN, dim light at night), we found that mice exposed to dLAN showed a significant weight gain compared with mice exposed to control standard light/dark (LD) photoperiod. To identify possible changes in the microbiota, we sampled two stages from the resting period of the circadian cycle of mice (ZT0 and ZT10) and evaluated them by high-throughput sequencing technology. Our results indicated that microbial diversity significantly differed between ZT0 and ZT10 in both LD and dLAN samples and that dLAN treatment impacted the taxonomic composition, functions, and interactions of mouse colonic microbiota. Together, these results show that bacterial taxa and microbial metabolic pathways might be involved with the mechanisms underlying weight gain in mice subjected to light contamination at night.

Assuntos

Colo/microbiologia , Microbioma Gastrointestinal , Poluição Luminosa/efeitos adversos , Aumento de Peso , Animais , Camundongos

RESUMO

Ae4 transporters are critical for Cl- uptake across the basolateral membrane of acinar cells in the submandibular gland (SMG). Although required for fluid secretion, little is known about the physiological regulation of Ae4. To investigate whether Ae4 is regulated by the cAMP-dependent signaling pathway, we measured Cl-/HCO3- exchanger activity in SMG acinar cells from Ae2-/- mice, which only express Ae4, and found that the Ae4-mediated activity was increased in response to ß-adrenergic receptor stimulation. Moreover, pretreatment with H89, an inhibitor of the cAMP-activated kinase (PKA), prevented the stimulation of Ae4 exchangers. We then expressed Ae4 in CHO-K1 cells and found that the Ae4-mediated activity was increased when Ae4 is coexpressed with the catalytic subunit of PKA (PKAc), which is constitutively active. Ae4 sequence analysis showed two potential PKA phosphorylation serine residues located at the intracellular NH2-terminal domain according to a homology model of Ae4. NH2-terminal domain Ser residues were mutated to alanine (S173A and S273A, respectively), where the Cl-/HCO3- exchanger activity displayed by the mutant S173A was not activated by PKA. Conversely, S273A mutant kept the PKA dependency. Together, we conclude that Ae4 is stimulated by PKA in SMG acinar cells by a mechanism that probably depends on the phosphorylation of S173.NEW & NOTEWORTHY We found that Ae4 exchanger activity in secretory salivary gland acinar cells is increased upon ß-adrenergic receptor stimulation. The activation of Ae4 was prevented by H89, a nonselective PKA inhibitor. Protein sequence analysis revealed two residues (S173 and S273) that are potential targets of cAMP-dependent protein kinase (PKA). Experiments in CHO-K1 cells expressing S173A and S273A mutants showed that S173A, but not S273A, is not activated by PKA.

Assuntos

Células Acinares/enzimologia , Antiportadores de Cloreto-Bicarbonato/metabolismo , Subunidades Catalíticas da Proteína Quinase Dependente de AMP Cíclico/metabolismo , Glândulas Salivares/enzimologia , Animais , Células CHO , Antiportadores de Cloreto-Bicarbonato/química , Antiportadores de Cloreto-Bicarbonato/genética , Cricetulus , Subunidades Catalíticas da Proteína Quinase Dependente de AMP Cíclico/genética , Feminino , Camundongos Endogâmicos C57BL , Camundongos Knockout , Modelos Moleculares , Mutação , Fosforilação , Conformação Proteica , Glândulas Salivares/citologia , Relação Estrutura-Atividade

RESUMO

Lubiprostone, a 20-carbon synthetic fatty acid used for the treatment of constipation, is thought to act through an action on Cl- channel ClC-2. Short chain fatty acids (SCFAs) are produced and absorbed in the distal intestine. We explore whether SCFAs affect ClC-2, re-examine a possible direct effect of lubiprostone on ClC-2, and use mice deficient in ClC-2 to stringently address the hypothesis that the epithelial effect of lubiprostone targets this anion channel. Patch-clamp whole cell recordings of ClC-2 expressed in mammalian cells are used to assay SCFA and lubiprostone effects. Using chamber measurements of ion current in mice deficient in ClC-2 or CFTR channels served to analyze the target of lubiprostone in the distal intestinal epithelium. Intracellular SCFAs had a dual action on ClC-2, partially inhibiting conduction but, importantly, facilitating the voltage activation of ClC-2. Intra- or extracellular lubiprostone had no effect on ClC-2 currents. Lubiprostone elicited a secretory current across colonic epithelia that was increased in mice deficient in ClC-2, consistent with the channel's proposed proabsorptive function, but absent from those deficient in CFTR. Whilst SCFAs might exert a physiological effect on ClC-2 as part of their known proabsorptive effect, ClC-2 plays no part in the lubiprostone intestinal effect that appears mediated by CFTR activation.

Assuntos

Agonistas dos Canais de Cloreto/uso terapêutico , Canais de Cloreto/efeitos dos fármacos , Ácidos Graxos Voláteis/metabolismo , Mucosa Intestinal/efeitos dos fármacos , Lubiprostona/uso terapêutico , Canais de Cloro CLC-2 , Agonistas dos Canais de Cloreto/farmacologia , Células HEK293 , Humanos , Lubiprostona/farmacologia

RESUMO

Withaferin A (WFA), a C5,C6-epoxy steroidal lactone isolated from the medicinal plant Withania somnifera (L.) Dunal, inhibits growth of tumor cells in different cancer types. However, the mechanisms underlying the effect of WFA on tumor cells are not fully understood. In the present study, we evaluated the blockade of TASK-3 channels by WFA in TASK-3-expressing HEK-293 cells. Explore if the WFA-mediated TASK-3 blockade can be used as a pharmacological tool to decrease the cell viability in cancer cells. A combination of functional experiments (patch-clamp, gene downregulation, overexpression and pharmacological inhibition) and molecular docking analysis were used to get insights into the mechanism by which the inhibition of TASK-3 by WFA affects the growth and viability of cancer cells. Withaferin A was found to inhibit the activity of TASK-3 channels. The inhibitory effect of Withaferin A on TASK-3 potassium currents was dose-dependent and independent of voltage. Molecular modeling studies identified putative WFA-binding sites in TASK-3 channel involved the channel blockade. In agreements with the molecular modeling predictions, mutation of residues F125 to A (F125A), L197 to V (L197 V) and the double mutant F125A-L197 V markedly decreased the WFA-induced inhibition of TASK-3. Finally, the cytotoxic effect of WFA was tested in MDA-MB-231 human breast cancer cells transfected with TASK-3 or shRNA that decreases TASK-3 expression. Together, our results show that the cytotoxic effect of WFA on fully transformed MDA-MB-231 cells depends on the expression of TASK-3. Herein, we also provide insights into the mechanism of TASK-3 inhibition by WFA.

Assuntos

Antineoplásicos Fitogênicos/farmacologia , Neoplasias da Mama/tratamento farmacológico , Proliferação de Células/efeitos dos fármacos , Bloqueadores dos Canais de Potássio/farmacologia , Canais de Potássio de Domínios Poros em Tandem/antagonistas & inibidores , Vitanolídeos/farmacologia , Antineoplásicos Fitogênicos/metabolismo , Sítios de Ligação , Neoplasias da Mama/genética , Neoplasias da Mama/metabolismo , Neoplasias da Mama/patologia , Linhagem Celular Tumoral , Feminino , Regulação Neoplásica da Expressão Gênica , Células HEK293 , Humanos , Potenciais da Membrana , Bloqueadores dos Canais de Potássio/metabolismo , Canais de Potássio de Domínios Poros em Tandem/genética , Canais de Potássio de Domínios Poros em Tandem/metabolismo , Ligação Proteica , Transdução de Sinais , Vitanolídeos/metabolismo

RESUMO

We would like to submit the following correction to our published paper [...].

RESUMO

The chemical composition of Mangifera indica L. cv. "Kent" leaves was determined by HPLC-ESI-QTOF-MS/MS. Polyphenolic compounds characterized as benzophenone derivatives were the main components found in extracts (1, maclurin 3-C-(2-O-galloyl)-D- glucoside isomer; 2, maclurin 3-C---D-glucoside; 3, iriflophenone 3-C---D-glucoside; 5, maclurin 3-C-(2,3-di-O-galloyl)---D-glucoside; 6, iriflophenone 3-C-(2-O-galloyl)---D-glucoside; 7, methyl-iriflophenone 3-C-(2,6-di-O-galloyl)---D-glucoside) and xanthones (4, mangiferin and 8, 6-O-galloyl-mangiferin). The estrogenic and antioxidant effects of aqueous extracts from Mangifera indica L. cv. "Kent" leaves on ovariectomized rats were determined by uterotrophic assay and malondialdehyde (MDA) levels in erythrocytes, bone, liver, and stomach. We conclude that the polyphenolic compounds from extracts act as exogenous antioxidant agents against oxidative damage in ovariectomized rats.

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La composición química de las hojas de Mangifera indica L. cv. "Kent" se determinó por HPLC-ESI-QTOF-MS/MS. Compuestos polifenólicos caracterizados como derivados de benzofenona fueron los componentes principales encontrados en los extractos (1, isómero de la maclurina 3-C-(2-O-galoyil)-D-glucósido; 2, maclurina 3-C-ß-D-glucósido; 3, iriflofenona 3-C-ß-D-glucósido; 5, maclurina 3-C-(2,3-di-O-galloíl)-ß-D-glucósido; 6, iriflofenona 3-C-(2-O-galloil)-ß-D-glucósido; 7, metil-iriflofenona 3-C-(2,6-di-O- galloyl)-ß-D-glucósido) y xantonas (4, mangiferina y 8, 6-O-galoyil-mangiferina). Los efectos estrogénicos y antioxidantes de los extractos acuosos de hojas de Mangifera indica L. cv. "Kent" en ratas ovariectomizadas se determinaron mediante ensayo uterotrófico y la medición de los niveles de malondialdehído (MDA) en eritrocitos, huesos, hígado y estómago. Concluimos que los compuestos polifenólicos de los extractos actúan como agentes antioxidantes exógenos contra el daño oxidativo en ratas ovariectomizadas.

Assuntos

Animais , Feminino , Ratos , Extratos Vegetais/farmacologia , Extratos Vegetais/química , Ovariectomia , Mangifera/química , Estrogênios/farmacologia , Antioxidantes/farmacologia , Estômago/efeitos dos fármacos , Benzofenonas/química , Osso e Ossos/efeitos dos fármacos , Peroxidação de Lipídeos/efeitos dos fármacos , Cromatografia Líquida de Alta Pressão , Espécies Reativas de Oxigênio , Ratos Sprague-Dawley , Folhas de Planta/química , Espectrometria de Massas por Ionização por Electrospray , Etanol , Espectrometria de Massas em Tandem , Fígado/efeitos dos fármacos , Malondialdeído , Antioxidantes/química

RESUMO

Two-pore domain K⁺ channels (K2P) display a characteristic extracellular cap structure formed by two M1-P1 linkers, the functional role of which is poorly understood. It has been proposed that the presence of the cap explains the insensitivity of K2P channels to several K⁺ channel blockers including tetraethylammonium (TEA). We have explored this hypothesis using mutagenesis and functional analysis, followed by molecular simulations. Our results show that the deletion of the cap structure of TASK-3 (TWIK-related acid-sensitive K⁺ channel) generates a TEA-sensitive channel with an IC50 of 11.8 ± 0.4 mM. The enhanced sensitivity to TEA displayed by the cap-less channel is also explained by the presence of an extra tyrosine residue at position 99. These results were corroborated by molecular simulation analysis, which shows an increased stability in the binding of TEA to the cap-less channel when a ring of four tyrosine is present at the external entrance of the permeation pathway. Consistently, Y99A or Y205A single-residue mutants generated in a cap-less channel backbone resulted in TASK-3 channels with low affinity to external TEA.

Assuntos

Canais de Potássio de Domínios Poros em Tandem/antagonistas & inibidores , Canais de Potássio Shab/antagonistas & inibidores , Tetraetilamônio/farmacologia , Sequência de Aminoácidos , Animais , Cobaias , Células HEK293 , Humanos , Simulação de Dinâmica Molecular , Mutação Puntual , Canais de Potássio de Domínios Poros em Tandem/química , Canais de Potássio de Domínios Poros em Tandem/genética , Canais de Potássio de Domínios Poros em Tandem/metabolismo , Ratos , Canais de Potássio Shab/química , Canais de Potássio Shab/genética , Canais de Potássio Shab/metabolismo

RESUMO

Functional and structural studies demonstrate that Cl(-) channels of the ClC family have a dimeric double-barrelled structure, with each monomer contributing an identical pore. Studies with ClC-0, the prototype ClC channel, show the presence of independent mechanisms gating the individual pores or both pores simultaneously. A single-point mutation in the CBS-2 domain of ClC-0 has been shown to abolish slow gating. We have taken advantage of the high conservation of CBS domains in ClC channels to test for the presence of a slow gate in ClC-2 by reproducing this mutation (H811A). ClC-2-H811A showed faster opening kinetics and opened at more positive potentials than ClC-2. There was no difference in [Cl(-)](i) dependence. Additional neutralization of a putative pore gate glutamate side chain (E207V) abolished all gating. Resolving slow and fast gating relaxations, however, revealed that the H811A mutation affected both fast and slow gating processes in ClC-2. This suggests that slow and fast gating in ClC-2 are coupled, perhaps with slow gating contributing to the operation of the pore E207 as a protopore gate.

Assuntos

Canais de Cloreto/metabolismo , Ativação do Canal Iônico/fisiologia , Rim/fisiologia , Potenciais da Membrana/fisiologia , Sequência de Aminoácidos , Substituição de Aminoácidos , Canais de Cloro CLC-2 , Linhagem Celular , Canais de Cloreto/química , Humanos , Cinética , Dados de Sequência Molecular , Mutagênese Sítio-Dirigida , Mutação , Porosidade , Estrutura Terciária de Proteína , Relação Estrutura-Atividade

RESUMO

The Cl- channel ClC-2 is expressed in transporting epithelia and has been proposed as an alternative route for Cl- efflux that might compensate for the malfunction of CFTR in cystic fibrosis. There is controversy concerning the cellular and membrane location of ClC-2, particularly in intestinal tissue. The aim of this paper is to resolve this controversy by immunolocalization studies using tissues from ClC-2 knockout animals as control, ascertaining the sorting of ClC-2 in model epithelial cells and exploring the possible molecular signals involved in ClC-2 targeting. ClC-2 was exclusively localized at the basolateral membranes of surface colonic cells or villus duodenal enterocytes. ClC-2 was sorted to the basolateral membranes in MDCK, Caco-2 and LLC-PK1-mu1B, but not in LLC-PK1-mu1A cells. Mutating a di-leucine motif (L812L813) to a di-alanine changed the basolateral targeting of ClC-2 to an apical location. The basolateral membrane localization of ClC-2 in absorptive cells of the duodenum and the colon is compatible with an absorptive function for this Cl- channel. Basolateral targeting information is contained in a di-leucine motif (L812L813) within CBS-2 domain at the C-terminus of ClC-2. It is speculated that ClC-2 also contains an apical sorting signal masked by L812L813. The proposal that CBS domains in ClC channels might behave as regulatory sites sensing intracellular signals opens an opportunity for pharmacological modulation of ClC-2 targeting.

Assuntos

Canais de Cloreto/biossíntese , Mucosa Intestinal/metabolismo , Motivos de Aminoácidos , Animais , Canais de Cloro CLC-2 , Células CACO-2 , Células Cultivadas , Canais de Cloreto/genética , Canais de Cloreto/metabolismo , Cães , Duodeno/citologia , Duodeno/metabolismo , Enterócitos/metabolismo , Humanos , Absorção Intestinal , Mucosa Intestinal/citologia , Leucina/metabolismo , Camundongos , Camundongos Knockout , Estrutura Terciária de Proteína , Ratos , Suínos , Distribuição Tecidual , Transfecção

RESUMO

BACKGROUND & AIMS: The principal function of the colon in fluid homeostasis is the absorption of NaCl and water. Apical membrane Na(+) channels, Na(+)/H(+), and Cl(-)/HCO(3)(-) exchangers have been postulated to mediate NaCl entry into colonocytes. The basolateral exit pathway for Cl(-) has recently been proposed to be via ClC-2 channels present in that membrane domain in surface epithelium. The aim of this report is to obtain functional data for a basolateral localization of ClC-2 and explore a possible direct regulation by intracellular Cl(-). METHODS: Guinea pig colon epithelium with the apical membrane perforated with nystatin in Ussing chambers is used to show a basolateral Cl(-) conductance. Gramicidin D perforated-patch configuration of the patch-clamp technique is used on isolated surface colonocytes. Heterologous expression of the recombinant channel and the whole-cell configuration are used to investigate a direct regulation by intracellular Cl(-). RESULTS: A basolateral membrane conductance with the characteristics of ClC-2 channels, including Cd(2+) sensitivity, selectivity, and inhibition by extracellular alkalinization, is present in distal colon epithelium. The effect of intracellular Cl(-) on this conductance suggests activation by the permeant anion. Using the recombinant ClC-2 channel, a strong dependence of its activity on intracellular Cl(-) is shown, with a shift of activation to more positive voltages as [Cl(-)](i) is increased. CONCLUSIONS: It is suggested that ClC-2 serves as an exit pathway for Cl(-) in the basolateral membranes of the distal colon and that its dependence on [Cl(-)](i) might provide a cross-talk mechanism to match fluxes at the apical and basolateral domains of these epithelial cells.

Assuntos

Canais de Cloreto/fisiologia , Cloretos/metabolismo , Colo/fisiologia , Mucosa Intestinal/fisiologia , Animais , Canais de Cloro CLC-2 , Cobaias , Ativação do Canal Iônico/fisiologia , Masculino , Técnicas de Patch-Clamp , Receptor Cross-Talk/fisiologia

RESUMO

Functional and structural studies demonstrate that Cl(-) channels of the ClC family have a dimeric double-barrelled structure, with each monomer contributing an identical pore. Single protopore gating is a fast process dependent on Cl(-) interaction within the selectivity filter and in ClC-0 has a low temperature coefficient over a 10 degrees C range (Q(10)). A slow gating process closes both protopores simultaneously, has a high Q(10), is facilitated by extracellular Zn(2+) and Cd(2+) and is abolished or markedly reduced by mutation of a cysteine conserved in ClC-0, -1 and -2. In order to test the hypothesis that similar slow and fast gates exist in the widely expressed ClC-2 Cl(-) channel we have investigated the effects of these manoeuvres on ClC-2. We find that the time constants of both components of the double-exponential hyperpolarization-dependent activation (and deactivation) processes have a high temperature dependence, with Q(10) values of about 4-5, suggesting important conformational changes of the channel. Mutating C256 (equivalent to C212 in ClC-0) to A, led to a significant fraction of constitutively open channels at all potentials. Activation time constants were not affected but deactivation was slower and significantly less temperature dependent in the C256A mutant. Extracellular Cd(2+), that inhibits wild-type (WT) channels almost fully, inhibited C256A only by 50%. In the WT, the time constants for opening were not affected by Cd(2+) but deactivation at positive potentials was accelerated by Cd(2+). This effect was absent in the C256A mutant. The effect of intracellular Cl(-) on channel activation was unchanged in the C256A mutant. Collectively our results strongly support the hypothesis that ClC-2 possesses a common gate and that part of the current increase induced by hyperpolarization represents an opening of the common gate. In contrast to the gating in ClC-0, the protopore gate and the common gate of ClC-2 do not appear to be independent.

Assuntos

Canais de Cloreto/metabolismo , Ativação do Canal Iônico/fisiologia , Animais , Canais de Cloro CLC-2 , Cádmio/farmacologia , Linhagem Celular , Canais de Cloreto/antagonistas & inibidores , Canais de Cloreto/genética , Eletrofisiologia , Humanos , Mutação , Ratos , Temperatura

RESUMO

ClC-2 is a ubiquitously expressed, two-pore homodimeric Cl- channel opened by hyperpolarisation. Little is known about its gating mechanisms. Crystallographic and functional studies in other ClC channels suggest that a conserved glutamate residue carboxylate side-chain can close protopores by interacting with a Cl--binding site in the pore. Competition for this site is thought to provide the molecular basis for gating by extracellular Cl-. We now show that ClC-2 gating depends upon intra- but not extracellular Cl- and that neutralisation of E217, the homologous pore glutamate, leads to loss of sensitivity to intracellular Cl- and voltage. Experiments testing for transient activation by extracellular protons demonstrate that E217 is not available for protonation in the closed channel state but becomes so after opening by hyperpolarisation. The results suggest that E217 is a hyperpolarisation-dependent protopore gate in ClC-2 and that access of intracellular Cl- to a site normally occupied by its side-chain in the pore stabilises the open state. A remaining hyperpolarisation-dependent gate might correspond to that closing both pores simultaneously in other ClC channels.

Assuntos

Canais de Cloreto/fisiologia , Cloretos/farmacologia , Ácido Glutâmico , Ativação do Canal Iônico/fisiologia , Substituição de Aminoácidos , Animais , Canais de Cloreto/genética , Sequência Conservada , Cobaias , Humanos , Concentração de Íons de Hidrogênio , Ativação do Canal Iônico/efeitos dos fármacos , Potenciais da Membrana , Mutagênese Sítio-Dirigida , Transfecção

RESUMO

The principal function of the colon in fluid homeostasis is the absorption of NaCl and water. Apical membrane Na(+) channels, Na(+)/H(+) and Cl(-)/HCO exchangers, have all been postulated to mediate NaCl entry into colonocytes. The identity of the basolateral exit pathway for Cl(-) is unknown. We have previously demonstrated the presence of the ClC-2 transcript in the guinea pig intestine. Now we explore in more detail, the tissue and cellular distribution of chloride channel ClC-2 in the distal colon by in situ hybridization and immunohistochemistry. The patch-clamp technique was used to characterize Cl(-) currents in isolated surface epithelial cells from guinea pig distal colon and these were compared with those mediated by recombinant guinea pig (gp)ClC-2. ClC-2 mRNA and protein were found in the surface epithelium of the distal colon. Immunolocalization revealed that, in addition to some intracellular labeling, ClC-2 was present in the basolateral membranes but absent from the apical pole of colonocytes. Isolated surface epithelial cells exhibited hyperpolarization-activated chloride currents showing a Cl(-) > I(-) permeability and Cd(2+) sensitivity. These characteristics, as well as some details of the kinetics of activation and deactivation, were very similar to those of recombinant gpClC-2 measured in parallel experiments. The presence of active ClC-2 type currents in surface colonic epithelium, coupled to a basolateral location for ClC-2 in the distal colon, suggests a role for ClC-2 channel in mediating basolateral membrane exit of Cl(-) as an essential step in a NaCl absorption process.

Assuntos

Canais de Cloreto/genética , Canais de Cloreto/fisiologia , Colo/química , RNA Mensageiro/análise , Animais , Canais de Cloro CLC-2 , Canais de Cloreto/análise , Cloretos/metabolismo , Condutividade Elétrica , Epitélio/química , Cobaias , Imuno-Histoquímica , Hibridização In Situ , Absorção Intestinal , Masculino , Técnicas de Patch-Clamp , Proteínas Recombinantes , Cloreto de Sódio/metabolismo

RESUMO

Harina entera de lupino dulce (Lupinus albus c.v. Multolupa) (39,6 por ciento de proteína, 13,0 por ciento en contenido graso), y carragenato fueron usados para incorporarlos a formulaciones comerciales de budín con el propósito específico de desarrollar un producto destinado a la población diabética que incluya una mezcla optimizada de estos ingredientes. Utilizando la metodología Superficie Respuesta, varias formulaciones experimentales de budín fueron preparadas y posteriormente evaluadas sensorialmente con el objeto de optimizar los ingredientes que pudieran afectar la calidad sensorial de las preparaciones de budín. Diferentes concentraciones de harina de lupino y carragenato fueron ensayadas en cada variable tres niveles de incorporación, totalizando nueve combinaciones de muestras para ser luego analizadas sensorialmente por un panel de 11 jueces entrenados. Para evaluar la calidad sensorial se empleó el test de puntaje compuesto determinando los siguientes parámetros: Apariencia, aroma, sabor, color, textura. Se concluye que el rango adecuado de concentraciones de harina de lupino es 7 por ciento-11 por ciento y carragenato entre 0,4 por ciento y 0,5, para ser incorporadas a la formulación de budín. Estos resultados fueron posteriormente confirmados con el test de aceptación hedónica

Assuntos

Dieta para Diabéticos , Farinha/análise