RESUMO
Gramicidin is a thoroughly studied cation ionophore widely used to experimentally manipulate the plasma membrane potential (PMP). In addition, it has been established that the drug, due to its hydrophobic nature, is capable of affecting the organization of membrane lipids. We have previously shown that modifications in the plasma membrane potential of epithelial cells in culture determine reorganizations of the cytoskeleton. To elucidate the molecular mechanisms involved, we explored the effects of PMP depolarization on some putative signaling intermediates. In the course of these studies, we came across some results that could not be interpreted in terms of the properties of gramicidin as an ionic channel. The purpose of the present work is to communicate these results and, in general, to draw attention to the fact that gramicidin effects can be misleadingly attributed to its ionic or electrical properties. In addition, this work also contributes with some novel findings of the modifications provoked on the signaling intermediates by PMP depolarization and hyperpolarization.
Assuntos
Gramicidina/metabolismo , Potenciais da Membrana/efeitos dos fármacos , Transdução de Sinais/efeitos dos fármacos , Animais , Bovinos , Membrana Celular/efeitos dos fármacos , Membrana Celular/metabolismo , Citoesqueleto/metabolismo , Células Endoteliais/efeitos dos fármacos , Células Endoteliais/metabolismo , Células Epiteliais/metabolismo , Gramicidina/efeitos adversos , Gramicidina/farmacologia , Canais Iônicos/metabolismo , Íons/metabolismo , Microtúbulos/metabolismo , Cultura Primária de Células , Transdução de Sinais/fisiologiaRESUMO
BACKGROUND: Gastric cancer is a common malignant tumor with high morbidity and mortality worldwide, which seriously affects human health. Gramicidin is a short peptide antibiotic which could be used for treating infection induced by bacteria or fungi. However, the anti-cancer effect of gramicidin on gastric cancer cells and its underlying mechanism remains largely unknown. RESULTS: Gastric cancer cells SGC-7901, BGC-823 and normal gastric mucosal cells GES-1 were treated with different concentrations of gramicidin respectively. The results of CCK-8 experiment revealed cellular toxicity of gramicidin to cancer cells while cell colony formation assay showed that gramicidin significantly inhibited the proliferation of gastric cancer cells, but had little effect on normal gastric mucosal cells. In addition, the wound healing assay showed that gramicidin inhibited the migration of SGC-7901 cell. Meanwhile, apoptosis and cell cycle analysis revealed that gramicidin induced cell apoptosis with G2/M cell cycle inhibition. Furthermore, western blot analysis demonstrated that gramicidin down-regulated the expression of cyclinD1 and Bcl-2 as well as the FoxO1 phosphorylation. CONCLUSIONS: The current study illustrated the anti-tumor activity of gramicidin on gastric cancer cells, providing a possibility for gramicidin to be applied in clinical practice for the treatment of gastric cancer.
Assuntos
Apoptose/efeitos dos fármacos , Ciclo Celular/efeitos dos fármacos , Movimento Celular/efeitos dos fármacos , Proliferação de Células/efeitos dos fármacos , Gramicidina/farmacologia , Neoplasias Gástricas/patologia , Linhagem Celular Tumoral , Ciclina D1/efeitos dos fármacos , Ciclina D1/metabolismo , Regulação para Baixo , Proteína Forkhead Box O1/efeitos dos fármacos , Proteína Forkhead Box O1/metabolismo , Humanos , Fosforilação , Proteínas Proto-Oncogênicas c-bcl-2/efeitos dos fármacos , Proteínas Proto-Oncogênicas c-bcl-2/metabolismoRESUMO
BACKGROUND: Gastric cancer is a common malignant tumor with high morbidity and mortality worldwide, which seriously affects human health. Gramicidin is a short peptide antibiotic which could be used for treating infection induced by bacteria or fungi. However, the anti-cancer effect of gramicidin on gastric cancer cells and its underlying mechanism remains largely unknown. RESULTS: Gastric cancer cells SGC-7901, BGC-823 and normal gastric mucosal cells GES-1 were treated with different concentrations of gramicidin respectively. The results of CCK-8 experiment revealed cellular toxicity of gramicidin to cancer cells while cell colony formation assay showed that gramicidin significantly inhibited the proliferation of gastric cancer cells, but had little effect on normal gastric mucosal cells. In addition, the wound healing assay showed that gramicidin inhibited the migration of SGC-7901 cell. Meanwhile, apoptosis and cell cycle analysis revealed that gramicidin induced cell apoptosis with G2/M cell cycle inhibition. Furthermore, western blot analysis demonstrated that gramicidin down-regulated the expression of cyclinD1 and Bcl-2 as well as the FoxO1 phosphorylation. CONCLUSIONS: The current study illustrated the anti-tumor activity of gramicidin on gastric cancer cells, providing a possibility for gramicidin to be applied in clinical practice for the treatment of gastric cancer.
Assuntos
Humanos , Neoplasias Gástricas/patologia , Ciclo Celular/efeitos dos fármacos , Movimento Celular/efeitos dos fármacos , Apoptose/efeitos dos fármacos , Proliferação de Células/efeitos dos fármacos , Gramicidina/farmacologia , Fosforilação , Regulação para Baixo , Proteínas Proto-Oncogênicas c-bcl-2/efeitos dos fármacos , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Ciclina D1/efeitos dos fármacos , Ciclina D1/metabolismo , Linhagem Celular Tumoral , Proteína Forkhead Box O1/efeitos dos fármacos , Proteína Forkhead Box O1/metabolismoRESUMO
Endocannabinoids are amphiphilic molecules that play crucial neurophysiological functions acting as lipid messengers. Antagonists and knockdown of the classical CB1 and CB2 cannabinoid receptors do not completely abolish many endocannabinoid activities, supporting the idea of a mechanism independent of receptors whose mode of action remains unclear. Here we combine gramicidin A (gA) single channel recordings and membrane capacitance measurements to investigate the lipid bilayer-modifying activity of endocannabinoids. Single channel recordings show that the incorporation of endocannabinoids into lipid bilayers reduces the free energy necessary for gramicidin channels to transit from the monomeric to the dimeric conformation. Membrane capacitance demonstrates that the endocannabinoid anandamide has limited effects on the overall structure of the lipid bilayers. Our results associated with the theory of membrane elastic deformation reveal that the action of endocannabinoids on membrane proteins can involve local adjustments of the lipid/protein hydrophobic interface. The current findings shed new light on the receptor-independent mode of action of endocannabinoids on membrane proteins, with important implications towards their neurobiological function.
Assuntos
Ácidos Araquidônicos/farmacologia , Membrana Celular/metabolismo , Endocanabinoides/farmacologia , Proteínas de Membrana/metabolismo , Alcamidas Poli-Insaturadas/farmacologia , Receptor CB1 de Canabinoide/metabolismo , Receptor CB2 de Canabinoide/metabolismo , Membrana Celular/efeitos dos fármacos , Gramicidina/farmacologia , Bicamadas Lipídicas/química , Fosfatidilcolinas/químicaRESUMO
Dioctadecyldimethylammonium bromide (DODAB) is an antimicrobial lipid that can be dispersed as large closed bilayers (LV) or bilayer disks (BF). Gramicidin (Gr) is an antimicrobial peptide assembling as channels in membranes and increasing their permeability towards cations. In mammalian cells, DODAB and Gr have the drawbacks of Gram-positive resistance and high toxicity, respectively. In this study, DODAB bilayers incorporating Gr showed good antimicrobial activity and low toxicity. Techniques employed were spectroscopy, photon correlation spectroscopy for sizing and evaluation of the surface potential at the shear plane, turbidimetric detection of dissipation of osmotic gradients in LV/Gr, determination of bacterial cell lysis, and counting of colony-forming units. There was quantitative incorporation of Gr and development of functional channels in LV. Gr increased the bilayer charge density in LV but did not affect the BF charge density, with localization of Gr at the BF borders. DODAB/Gr formulations substantially reduce Gr toxicity against eukaryotic cells and advantageously broaden the antimicrobial activity spectrum, effectively killing Escherichia coli and Staphylococcus aureus bacteria with occurrence of cell lysis.
Assuntos
Antibacterianos/química , Peptídeos Catiônicos Antimicrobianos/química , Cátions/química , Gramicidina/química , Antibacterianos/farmacologia , Peptídeos Catiônicos Antimicrobianos/farmacologia , Cátions/farmacologia , Escherichia coli/efeitos dos fármacos , Gramicidina/farmacologia , Viabilidade Microbiana/efeitos dos fármacos , Nanopartículas/química , Compostos de Amônio Quaternário/química , Staphylococcus aureus/efeitos dos fármacosRESUMO
Previous work from our laboratory and others has shown that, in some epithelia, the epithelial sodium channel (ENaC) increases its expression during wound healing. In these cases, inhibition of the channel determines a decrease in the healing rate, a result suggesting a role for ENaC in the overall healing process. To understand further this role of ENaC in epithelia, we explored the participation of ENaC in wound healing in four cultured epithelial cell lines selected on the basis of their different embryonic origins, function and modality of healing, i.e., by lamellipodial cell crawling or by actin cable formation. Three of the cell lines (bovine corneal endothelial cells, rabbit corneal epithelial cells and Madin-Darby canine kidney cells) exhibited an increase in ENaC expression and consequent membrane potential depolarization and an increase in cytosolic sodium and calcium, whereas one line (bovine aortal endothelial cells, BAEC) did not exhibit any of these changes. In all of the cell lines, however, ENaC inhibition determined a similar decrease in the rate of wound healing. In BAEC monolayers, the increase in ENaC activity produced plasma membrane depolarization, increased cytosolic sodium and calcium, and augmented the velocity of healing. These novel findings contribute to the idea that ENaC plays a critical role in wound healing in various epithelia, independently of the modality of healing and of any increase in the expression of the channel.
Assuntos
Aorta Torácica/metabolismo , Córnea/metabolismo , Canais Epiteliais de Sódio/metabolismo , Cicatrização/fisiologia , Animais , Antibacterianos/farmacologia , Aorta Torácica/citologia , Aorta Torácica/lesões , Bovinos , Linhagem Celular , Colforsina/farmacologia , Córnea/citologia , Lesões da Córnea , Cães , Células Epiteliais/metabolismo , Bloqueadores do Canal de Sódio Epitelial/farmacologia , Canais Epiteliais de Sódio/biossíntese , Epitélio/imunologia , Epitélio/metabolismo , Gramicidina/farmacologia , Células Madin Darby de Rim Canino , Potenciais da Membrana/fisiologia , Coelhos , Vasodilatadores/farmacologiaRESUMO
This work presents experimental results combined with model-dependent predictions regarding the osmotic-permeability regulation of human aquaporin 1 (hAQP1) expressed in Xenopus oocyte membranes. Membrane elastic properties were studied under fully controlled conditions to obtain a function that relates internal volume and pressure. This function was used to design a model in which osmotic permeability could be studied as a pressure-dependent variable. The model states that hAQP1 closes with membrane-tension increments. It is important to emphasize that the only parameter of the model is the initial osmotic permeability coefficient, which was obtained by model-dependent fitting. The model was contrasted with experimental records from emptied-out Xenopus laevis oocytes expressing hAQP1. Simulated results reproduce and predict volume changes in high-water-permeability membranes under hypoosmotic gradients of different magnitude, as well as under consecutive hypo- and hyperosmotic conditions. In all cases, the simulated permeability coefficients are similar to experimental values. Predicted pressure, volume, and permeability changes indicate that hAQP1 water channels can transit from a high-water-permeability state to a closed state. This behavior is reversible and occurs in a cooperative manner among monomers. We conclude that hAQP1 is a constitutively open channel that closes mediated by membrane-tension increments.
Assuntos
Aquaporina 1/metabolismo , Membrana Celular/fisiologia , Ativação do Canal Iônico , Animais , Simulação por Computador , Elasticidade , Gramicidina/farmacologia , Humanos , Modelos Biológicos , Oócitos/fisiologia , Osmose , Tensão Superficial , Xenopus laevisRESUMO
Modifications in the cell membrane potential have been suggested to affect signaling mechanisms participating in diverse cellular processes, many of which involve structural cellular alterations. In order to contribute some evidence in this respect, we explored the effects of several depolarizing procedures on the structure and monolayer organization of bovine corneal endothelial cells in culture. Visually confluent cell monolayers were incubated with or without the depolarizing agent, either in a saline solution or in culture medium for up to 30 min. Membrane potential was monitored by fluorescence microscopy using oxonol V. Fluorescent probes were employed for F-actin, microtubules, and vinculin. Depolarization of the plasma membrane, achieved via the incorporation of gramicidin D into confluent endothelial cells or by modifications of the extracellular saline composition, provoked an increment of oxonol fluorescence and changes in cell morphology, consisting mainly of modifications in the cytoskeletal organization. In some areas, noticeable intercellular spaces appear. The cytoskeleton modifications mainly consist of a marked redistribution of F-actin and microtubules, with accompanying changes in vinculin localization. The results suggest that the depolarization of the plasma membrane potential may participate in mechanisms involved in cytoskeleton organization and monolayer continuity in corneal endothelial cells in culture.
Assuntos
Comunicação Celular/fisiologia , Membrana Celular/metabolismo , Córnea/metabolismo , Citoesqueleto/metabolismo , Células Epiteliais/metabolismo , Citoesqueleto de Actina/efeitos dos fármacos , Citoesqueleto de Actina/metabolismo , Citoesqueleto de Actina/ultraestrutura , Animais , Bovinos , Comunicação Celular/efeitos dos fármacos , Membrana Celular/efeitos dos fármacos , Membrana Celular/ultraestrutura , Células Cultivadas , Colina/farmacologia , Córnea/citologia , Córnea/efeitos dos fármacos , Citoesqueleto/efeitos dos fármacos , Citoesqueleto/ultraestrutura , Células Epiteliais/citologia , Células Epiteliais/efeitos dos fármacos , Espaço Extracelular/efeitos dos fármacos , Espaço Extracelular/metabolismo , Gluconatos/farmacologia , Gramicidina/farmacologia , Imuno-Histoquímica , Isoxazóis , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Microtúbulos/efeitos dos fármacos , Microtúbulos/metabolismo , Microtúbulos/ultraestrutura , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/fisiologia , Cloreto de Sódio/metabolismo , Vinculina/efeitos dos fármacos , Vinculina/metabolismoRESUMO
The K+ and Cl- currents activated by Ca2+-ionophore treatment or by hypotonic cell swelling have been studied in Ehrlich ascites tumour cells by the patch-clamp technique. A charybdotoxin-inhibitable K+ current was activated by increasing intracellular Ca2+ concentration. In contrast, the K+ current activated by cell swelling was insensitive to charybdotoxin as well as to apamin, suggesting that channels different from those sensitive to Ca2+ are responsible for regulatory volume adjustments in these cells. The magnitude of the K+ and Cl- currents activated by hypotonic challenge was markedly temperature-dependent, possibly reflecting the temperature-dependence of enzymes involved in the intracellular signalling of cell volume regulation.
Assuntos
Cálcio/fisiologia , Carcinoma de Ehrlich/fisiopatologia , Canais de Potássio/fisiologia , Animais , Apamina/farmacologia , Carcinoma de Ehrlich/patologia , Tamanho Celular , Charibdotoxina/farmacologia , Canais de Cloreto/fisiologia , Gramicidina/farmacologia , Ionomicina/farmacologia , Ionóforos/farmacologia , Potenciais da Membrana , Pressão Osmótica , Técnicas de Patch-Clamp , Bloqueadores dos Canais de Potássio , Temperatura , Células Tumorais CultivadasRESUMO
Exposure of NIH/3T3 fibroblasts not expressing P-glycoprotein to 50, 30, 20, and 10% hyposmotic solutions led to cell volume increases of 70, 32, 21, and 12%, respectively. After swelling, NIH/3T3 cells exhibited regulatory volume decrease (RVD), attaining complete volume recovery after 30 min except in 50% hyposmotic solution, in which volume recovery was 76%. RVD was accelerated by gramicidin and inhibited by the Cl channel blockers 5-nitro-2-(3-phenylpropylamino)-benzoic acid, 1,9-dideoxyforskolin, dipyridamole, and niflumic acid and by the K channel, blocker quinidine. RVD was reduced 15% by removal of extracellular Ca. The pathway opened by hypotonicity was highly permeable to K and Rb and only partly permeable to other cations. Most anions were able to permeate, with a permeability ranking of nitrate > benzoate = iodide > thiocyanate > chloride > > gluconate. The pathway was permeable to neutral amino acids, with a permeability ranking of glycine > alanine > glutamate > taurine > gamma-aminobutyric acid > glutamine. The pathway was not permeable to basic amino acids. These results show that, despite the absence of P-glycoprotein, NIH/3T3 cells exhibit RVD with properties similar to those expressed in most cell types.
Assuntos
Membro 1 da Subfamília B de Cassetes de Ligação de ATP/fisiologia , Ânions/metabolismo , Canais de Cloreto/fisiologia , Cloretos/metabolismo , Equilíbrio Hidroeletrolítico/fisiologia , Células 3T3 , 4-Aminopiridina/farmacologia , Membro 1 da Subfamília B de Cassetes de Ligação de ATP/análise , Animais , Bário/farmacologia , Permeabilidade da Membrana Celular , Canais de Cloreto/antagonistas & inibidores , Cloretos/farmacologia , Colchicina/toxicidade , Colforsina/análogos & derivados , Colforsina/farmacologia , Dipiridamol/farmacologia , Gramicidina/farmacologia , Cinética , Camundongos , Ácido Niflúmico/farmacologia , Nitrobenzoatos/farmacologia , Bloqueadores dos Canais de Potássio , Canais de Potássio/fisiologia , Quinidina/farmacologia , Tetraetilamônio , Compostos de Tetraetilamônio/farmacologia , Fatores de Tempo , Equilíbrio Hidroeletrolítico/efeitos dos fármacosRESUMO
Tityustoxin (TsTX), a toxin obtained from the venom of the Brazilian scorpion Tityus serrulatus, stimulates Na+ influx through tetrodotoxin (TTX)-sensitive Na+ channels which, in turn, promotes both Ca(2+)-dependent and Ca(2+)-independent release of glutamate from rat cerebrocortical synaptosomes. The level of Ca(2+)-dependent glutamate release after addition of 0.5 microM TsTX is greater than that produced by a maximally depolarizing concentration of KCl. This effect of TsTX, which is entirely dependent on Na+ entry, suggests that Na+ has a role in modulating Ca2+ entry and glutamate release that is not simply related to membrane depolarization. In order to investigate possible modulatory role(s) of Na+ on Ca(2+)-dependent glutamate release, we compared the effects of TsTX with those of KCl and the Na+ ionophore gramicidin D. When used alone, 100 nM gramicidin D produced a larger increase in intrasynaptosomal free Na+ than did 0.5 microM TsTX, and a similar rise in intrasynaptosomal free Ca2+, but was much less effective in promoting glutamate release. Even the combination of membrane depolarization (by 33 mM KCl) and elevation of intrasynaptosomal free Na+ (by 100 nM gramicidin) was still less effective than TsTX at causing Ca(2+)-dependent glutamate release. These data suggest that localized Na+ entry, through TTX-sensitive Na+ channels, exerts a modulatory role on Ca(2+)-dependent glutamate release from nerve endings in the cerebral cortex.
Assuntos
Cálcio/farmacologia , Ácido Glutâmico/metabolismo , Canais de Sódio/fisiologia , Sódio/metabolismo , Sinaptossomos/metabolismo , Tetrodotoxina/farmacologia , Animais , Córtex Cerebral/metabolismo , Gramicidina/farmacologia , Masculino , Cloreto de Potássio/farmacologia , Ratos , Ratos Wistar , Venenos de Escorpião/farmacologia , Sinaptossomos/efeitos dos fármacosRESUMO
The water permeability properties of ovarian oocytes from Xenopus laevis and Bufo arenarum, a toad species found in the Buenos Aires region, were studied. We report that: (i) the water osmotic permeability (Pf, cm/sec x 10(-4)) was significantly higher in Bufo (6 degrees C = 12.3 +/- 2.4; 18 degrees C = 20.8 +/- 4.8) than in Xenopus oocytes (6 degrees C = 5.3 +/- 0.3; 18 degrees C = 6.2 +/- 1.6). The corresponding water diffusion permeability values (Pd, cm/sec x 10(-4)) were: Xenopus = 2.3 +/- 0.3 (6 degrees C) and 4.8 +/- 0.7 (18 degrees C); Bufo = 2.7 +/- 0.4 (6 degrees C) and 6.0 +/- 0.5 (18 degrees C). (ii) Amphotericin B increased the Pf and Pd values. The observed delta Pf/delta Pd ratio was not significantly different from the expected results (n = 3), after amphotericin B incorporation in both species. This means that the influence of unstirred layers and other potential artifactual compounds did not significantly affect our experimental results. (iii) Preincubation with gramicidin during 12 hr induced a clear increase in the oocyte volume. After that, a hypotonic shock only slightly increased the oocyte volume. Conversely, a hypertonic challenge induced a volume change significantly higher than the one observed in control conditions. (iv) Mercury ions did not affect the osmotic permeability in Xenopus oocytes but clearly inhibited, in a reversible way, the osmotic permeability in oocytes from B. arenarum. (v) Mercury ions did not reduce Pd values in either species.(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Bufo arenarum/fisiologia , Permeabilidade da Membrana Celular/fisiologia , Oócitos/citologia , Ovário/citologia , Água/fisiologia , Xenopus laevis/fisiologia , Anfotericina B/farmacologia , Animais , Membrana Celular/fisiologia , Membrana Celular/ultraestrutura , Permeabilidade da Membrana Celular/efeitos dos fármacos , Feminino , Gramicidina/metabolismo , Gramicidina/farmacologia , Mercúrio/farmacologia , Oócitos/fisiologia , Oócitos/ultraestrutura , Osmose/efeitos dos fármacos , Osmose/fisiologiaRESUMO
PhTX2, one of the components of the venom of the South American spider Phoneutria nigriventer, inhibits the closure of voltage-sensitive Na+ channels. Incubation of cerebral-cortical synaptosomes with PhTX2 causes a rapid increase in the intrasynaptosomal free Ca2+ concentration and a dose-dependent release of glutamate. This release is made up of a slow component, which appears to be due to reversal of Na(+)-dependent glutamate uptake, and more rapid component that is dependent on the entry of extrasynaptosomal Ca2+. It has previously been shown that membrane depolarization using KCl can cause rapid Ca(2+)-dependent release of glutamate from synaptosomes. This requires Ca2+ entry through a specific type of Ca2+ channel that is sensitive to Aga-GI, a toxic component of the venom of the spider Agelenopsis aperta. We have compared the effects of PhTX2 and KCl on elevation of intrasynaptosomal free Ca2+ and glutamate release, and a number of differences have emerged. Firstly, PhTX2-mediated Ca2+ influx and glutamate release, but not those caused by KCl, are inhibited by tetrodotoxin. Secondly, KCl produces a clear additional increase in Ca2+ and glutamate release following those elicited by PhTX2. Finally, 500 microM MnCl2 abolishes PhTX2-mediated, but not KCl-mediated, glutamate release. These findings suggest that more than one mechanism of Ca2+ entry may be coupled to glutamate release from nerve endings.
Assuntos
Córtex Cerebral/metabolismo , Glutamatos/metabolismo , Neuropeptídeos/toxicidade , Neurotoxinas/toxicidade , Cloreto de Potássio/farmacologia , Sinaptossomos/metabolismo , Animais , Cloretos/farmacologia , Ácido Glutâmico , Gramicidina/farmacologia , Cinética , Masculino , Compostos de Manganês/farmacologia , Ratos , Ratos Wistar , Sódio/metabolismo , Canais de Sódio/efeitos dos fármacos , Canais de Sódio/fisiologia , Venenos de Aranha/toxicidade , Sinaptossomos/efeitos dos fármacos , Tetrodotoxina/toxicidadeRESUMO
A fim de avaliar a sensibilidade "in vitro" à associaçäo de sulfato de framicetina, sulfato de polimixina B e gramicidina, estudamos amostras de 96 pacientes portadores de patologias oculares externas e de 4 lentes de contato gelatinosas. De 112 antibiogramas realizados, 80 (71,4%) foram por Staphylococcus aureus, cuja sensibilidade incluindo todas as bactérias de 85,7% (96). Esta associaçäo é composta por 3 antibióticos bactericidas näo usados sistematicamente de rotina
Assuntos
Humanos , Masculino , Feminino , Framicetina/farmacologia , Gramicidina/farmacologia , Técnicas In Vitro , Polimixina B/farmacologia , Soluções Oftálmicas/provisão & distribuição , BrasilRESUMO
The cationic amphiphilic polypeptide gramicidin S inhibits the Ca2+-ATPase of human red-cell membranes by lowering the maximum velocity of the high-affinity component and the apparent affinity of the low-affinity component of the velocity-versus-ATP concentration curve of the enzyme. Gramicidin S does not alter the apparent affinity of the Ca2+-ATPase for Ca2+. Calmodulin is not essential for the inhibition, but increases the sensitivity of the enzyme to the inhibitor. The effects of gramicidin S on the Ca2+-ATPase can be reversed with phosphatidylcholine vesicles but not with buffer solutions, suggesting that gramicidin S acts from the lipid phase of the membrane.