Monensin 26-pyromellitate forms lithium channels in monolayer lipid membranes

Fuhrhop, Jürgen‐Hinrich; Liman, Ulrich

doi:10.1021/ja00328a072

Cited by 48 publications

(26 citation statements)

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“…It is clear, for example, that for a given surfactant vesicle, several different sites can be identified: at the water pool-head group interface of both monolayers there are relatively hydrophilic sites where surface-active molecules frequently are solubilized. 31 For complex surfactants such as phospholipids there exists the possibility of solubilization within the bilayer, but in a region of intermediate hydrophobicity, where polar groups are at least partially "solvated" by water but there is also some of the structural organization associated with the "crystalline" hydrocarbon chains below one phase transition temperature. Finally there should exist within the vesicle solu-(12) Otruba, J. P.; Whitten, D. G. J.…”

Section: Discussionmentioning

confidence: 99%

Photochemical reactions in organized assemblies. 44. Surfactant and hydrophobic derivatives of trans-stilbenes as probes of vesicle and micelle solubilization sites. Studies using fluorescence and photoisomerization as probes

Suddaby¹,

Brown²,

Russell³

et al. 1985

J. Am. Chem. Soc.

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Section: Discussionmentioning

confidence: 99%

Photochemical reactions in organized assemblies. 44. Surfactant and hydrophobic derivatives of trans-stilbenes as probes of vesicle and micelle solubilization sites. Studies using fluorescence and photoisomerization as probes

Suddaby¹,

Brown²,

Russell³

et al. 1985

J. Am. Chem. Soc.

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“…Liposomes were prepared from egg phosphatidy lcholine and lipid concentrations ranged from 8.4 to 1 1.2 mg ~r r -~. (b) Extent of entry of Na+ into liposomes as a function of time in the presence of CMo( 7 ) and CUc (V), and in their absence (+). The lines are simply a guide for the eye Liposomes were prepared from a mixture of egg FC, DPPC, stearylamine and cholesterol.…”

mentioning

confidence: 99%

Channel-type molecular structures. Part 4. Transmembrane transport of alkali-metal ions by ‘bouquet’ molecules

Pregel¹,

Jullien²,

Canceill³

et al. 1995

J. Chem. Soc., Perkin Trans. 2

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This report describes transport experiments with 'bouquet' molecules designed to act as artificial ion channels. The 'bouquets' are based on a central macrocycle w h i c h is either an 18-crown-6 (BM) or a cyclodextrin derivative ( BcD) to which are attached poly(ethy1ene oxide) [poly(oxyethylene)] chains (BMo and BcDo) or polyalkyl chains (B," and B,,") tipped with carboxylate endgroups. The 'bouquets' were studied in liposomes prepared from egg phosphatidylcholine (egg PC), dipalmitoyl phosphatidylcholine (DPPC) and a mixture of egg PC, stearylamine and cholesterol. Opposing gradients in Li' and Na' concentration were created and the transport of alkali-metal ions down their concentration gradients was followed directly b y 'Li and 23Na N M R spectroscopy. 'Bouquets' were found to cause a one-for-one exchange of Na' for Li' (antiport). In order to estimate transport rates, the extent of Na' entry into liposomes was followed as a function of time. All 'bouquets' transported ions at similar rates in fluid membranes. Comparison of transport rates in fluid-(egg PC) and gel-state membranes (DPPC) was used to distinguish carrier and channel mechanisms. Control experiments demonstrated that a k n o w n carrier (monensin A) gave significantly lower transport rates in gel-state membranes. T w o 'bouquets', B," and Bc-O, were found to transport Na' at similar rates in fluid-and gel-state membranes; this suggests that ion passage occurs preferentially b y the channel mechanism and not by the carrier mechanism. Variation of transport rate with 'bouquet' concentration was probed for BMo and BMC and the rates were found to increase with BMc concentration but not with BMo concentration. Since the transport rate is expected t o be proportional t o transporter concentration in both the carrier and channel mechanisms, this indicates that BMo uses neither a carrier nor a channel mechanism. The mechanism b y which 'bouquet' molecules operate and the criteria which may be used to decide whether functioning channels have been created are discussed.

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“…Previous studies with low concentrations of surfactants also reported an increase in membrane permeability but did not systematically measure changes in the liposome or vesicle morphology. , In the present studies, however, the compounds are not surfactants nor do they contain long hydrocarbon chains. More importantly, the vanadocene complexes are much shorter than the 30−40 Å required to span the bilayer and form channels . Therefore, the mechanism of activity of these organometallic complexes to cause such effects is likely to be quite different from that of the surfactants or ionophores.…”

Section: Discussionmentioning

confidence: 99%

“…Polypeptides, macrocyclic ionophores, and polymeric crown ethers 4 form artificial channels by spanning the bilayer. It has been shown that to form such a channel, it is optimal for the compound to have hydrophilic end groups, lipophilic portions in the channel, and appropriate infrastructural size to span the bilayer, which is approximately 40 Å. 4a, Low levels of surfactants and polymers have been found to increase the permeability of liposomes without destroying the membrane. − Triton X-100 is postulated to form inverted micelle structures within the bilayer, promoting both permeability and membrane fusion . The model proposed by Regen et al for surfactants, bolaphiles, and polymers implies that the leakage of dye from the vesicle is due to aggregates of surfactant causing membrane rupture 7c.…”

Section: Introductionmentioning

confidence: 99%

Interactions of Vanadocene(IV)-Chelated Complexes with Artificial Membranes

1998

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The membrane interactions of five vanadocene(IV)-chelated complexes, which are very effective spermicidal agents, have been studied using zwitterionic and negative unilamellar liposomes. In permeability studies, bis(cyclopentadienyl)vanadium(IV) (2,2‘-bipyridine)trifluoromethanesulfonate (1) and bis(cyclopentadienyl)vanadium(IV) (phenyl benzohydroxamato)trifluoromethanesulfonate (2) cause the release of about 35% and 20% encapsulated carboxyfluorescein, respectively, in both types of liposomes, whereas the congeneric vanadocene derivatives of diethyl dithiocarbamate (3), acetyl acetonate (4), and catecholate (5) have little or no effect on the permeability. Of the five compounds, only 4 and 1 initiate peroxidation of the lipids. None of the vanadocene-chelated complexes cause appreciable liposome aggregation, fusion, or changes in packing order of the liposomes as observed from UV/vis spectroscopy, fluorescence energy resonance transfer, and fluorescence polarization studies. The ability of the two vanadocene derivatives (1 and 2) to cause the liposomes to become permeable is therefore not related to the extent of peroxidation of the lipids or to complete disruption of the membrane. We propose that these vanadocene-chelated complexes have unique configurational preferences which alter the membrane by intercalation, creating “leaky patches” in the liposomal membrane.

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Monensin 26-pyromellitate forms lithium channels in monolayer lipid membranes

Cited by 48 publications

References 0 publications

Photochemical reactions in organized assemblies. 44. Surfactant and hydrophobic derivatives of trans-stilbenes as probes of vesicle and micelle solubilization sites. Studies using fluorescence and photoisomerization as probes

Photochemical reactions in organized assemblies. 44. Surfactant and hydrophobic derivatives of trans-stilbenes as probes of vesicle and micelle solubilization sites. Studies using fluorescence and photoisomerization as probes

Channel-type molecular structures. Part 4. Transmembrane transport of alkali-metal ions by ‘bouquet’ molecules

Interactions of Vanadocene(IV)-Chelated Complexes with Artificial Membranes

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