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Biomedical subjects

W Stillwell

Publications and source records attributed to W Stillwell.

At least 55 records · Page 3Linked to original sources
PubMed1988

Abscisic acid enhances aggregation and fusion of phospholipid vesicles.

The plant hormone abscisic acid (ABA) is shown to enhance the aggregation and fusion of small unilamellar lipid vesicles composed of 80 mol% dimyristoylphosphatidylcholine (DMPC) and 20 mol% dimyristoylphosphatidylcholine (DMPE). Aggregation and fusion did not occur with single component (100 mol%) DMPC vesicles. Fusion was followed by two fundamentally different techniques, fluorescence resonance energy transfer which monitors intermixing of bilayers and ANTS-DPX which monitors intermixing of the sequestered aqueous interiors. It is suggested that a previously unreported role of ABA may be as a membrane fusagen.

Abscisic Acid↗
PubMed1988

Electron spin resonance study of the interactions of retinoids with a phospholipid model membrane.

The effects of up to 20 mol% incorporation of all-trans-retinol (vitamin A), retinal (vitamin A aldehyde) and retinoic acid (vitamin A acid) on acyl chain order and dynamics in liquid crystalline dipalmitoylphosphatidylcholine membranes at pH 7.5 were studied by electron spin resonance (ESR) of 5-, 7-, 10-, 12- and 16-doxyl spin-labelled stearic acids intercalated into the membrane. Order parameters S and correlation times tau c determined from the ESR spectra demonstrate that the influence of retinoic acid differs from retinol or retinal. Whereas the latter two retinoids have negligible effect (less than 1%) on acyl chain order towards the membrane surface (5 position), retinoic acid reduces the order parameter by as much as 8% at 20 mol% incorporation. All three retinoids restrict acyl chain motion to a similar extent approaching the center of membrane (10, 12 and 16 positions), where up to 22% increases in order parameter and correlation time were observed. Complementary osmotic swelling and carboxyfluorescein release measurements show that the enhancement in permeability of egg phosphatidylcholine membranes to erythritol and carboxyfluorescein is greater with all-trans-retinoic acid than all-trans-retinol or retinal.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1988

Effect of fish oils on rat plasma lipoproteins.

Plasma high (HDL) and low (LDL) density lipoproteins were isolated from rats fed a diet supplemented with either fish (menhaden) oil or hydrogenated coconut oil (control). Fluorescence polarization and electron spin resonance of labelled fatty acid probe molecules incorporated into the outer amphiphilic monolayer of HDL indicate molecular motion is restricted in the upper portion of the acyl chain following the fish oil diet, which is consistent with a 'hook' conformation predicted by preliminary molecular model calculations for n-3 fatty acids (the predominant component of fish oil). Negligible dependence on diet was observed in LDL. Thus, a HDL specific effect of dietary fish oil on molecular fluidity and order in the outer monolayer of rat lipoproteins is suggested.

Animals↗
PubMed1988

Geraniol interferes with membrane functions in strains of Candida and Saccharomyces.

Geraniol, an olefinic terpene, was found to inhibit growth of Candida albicans and Saccharomyces cerevisiae strains. Geraniol was shown to enhance the rate of potassium leakage out of whole cells and also was shown by fluorescence polarization to increase C. albicans membrane fluidity. Biophysical studies using differential scanning calorimetry, fluorescence polarization and osmotic swelling of phospholipid vesicles demonstrated that geraniol decreased the phase-transition temperature of dipalmitoylphosphatidylcholine vesicles, affected fluidity throughout the bilayer, particularly the central portion of the bilayers, and caused an increase in bilayer permeability to erythritol. Geraniol may have potential use as an antifungal agent.

Acyclic Monoterpenes↗
PubMed1987

Membrane-directed effects of the plant hormones abscisic acid, indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid.

This study examines two ways plant hormones might influence membrane processes, effects on overall permeability and modifications of specific ion channels. Abscisic acid (ABA) and indole-3-acetic acid (IAA) greatly enhanced erythritol permeability in mixed egg lecithin bilayers. In single component dioleoylphosphatidylcholine bilayers ABA was less effective than IAA, while 2,4-dichlorophenoxyacetate (2,4-D) did not affect either system or alter their ABA response. In Myxicola axons ABA and IAA had no effect, while 2,4-D (10 uM) caused a depolarizing shift of voltage-dependent Na+ and K+ activation by 25 +/- 4 mV and 15 +/- 3 mV, consistent with internal negative surface charge changes of -0.002 e-/A2 and -0.0007 e-/A2. We conclude that both generalized and ion channel-directed effects may link plant hormones and intracellular regulation.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1985

Abscisic acid increases lipid bilayer permeability to cations as studied by phosphorus-31 NMR.

Using a 31P-NMR lanthanide shift technique, abscisic acid is shown to enhance the permeability to praeseodymium of lipid bilayers composed of 80 mol% phosphatidylcholine and 20 mol% phosphatidylethanolamine. Praeseodymium permeability is immeasurably slow in the absence of the hormone whether or not phosphatidylethanolamine is present in the bilayers. Only in the presence of abscisic acid is praeseodymium permeability observed, the effect being significantly greater when phosphatidylethanolamine is present. These results substantiate prior reports from nonelectrolyte permeability studies that abscisic acid interacts with phosphatidylethanolamine in lipid bilayers.

Abscisic Acid↗
PubMed1983

Kinetin increases water permeability of phosphatidylcholine lipid bilayers.

Kinetin is shown to increase substantially the water permeability of liposomes composed of several types of phosphatidylcholines including the natural phospholipids egg lecithin and asolectin and the synthetic phospholipids dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine. Kinetin effects were measured from 16.3 micromolar to 2.4 millimolar at temperatures from 10 degrees C to 50 degrees C and at pH 2.0, 7.0, and 11.0. Temperature studies indicate that kinetin produces a larger increase in water permeability with membranes in the more fluid liquid crystalline state. Kinetin is also shown to enhance [(14)C]glucose permeability and perhaps promotes membrane aggregation. From these experiments, we conclude that kinetin may produce its initial effect by altering the lipid bilayer portion of membranes.

Journal Article↗
PubMed1983

Effect of retinol and retinoic acid on P/O ratios of coupled mitochondria.

Retinol at levels above 0.5 n moles/mg protein and retinoic acid at levels above 0.25 n moles/mg protein are shown to uncouple mitochondrial oxidative phosphorylation. Uncoupling is measured with the substrates ascorbate plus N,N,N',N'-tetra-methyl-p-phenylenediamine, succinate and beta-hydroxybutyrate. These experiments indicate that the uncoupling effects of retinol and retinoic acid are not site specific but likely are the result of the vitamin being a general membrane bilayer disrupting agent.

2,4-Dinitrophenol↗
PubMed1982

Effect of retinol and retinoic acid on permeability, electrical resistance and phase transition of lipid bilayers.

Retinol and retinoic acid have been incorporated into the artificial membrane systems, planar bimolecular lipid membranes and liposomes, and their effects on several membrane parameters have been measured. 1. Retinol and retinoic acid increased the permeability of egg lecithin liposomes to K+, I- and glucose when incorporated into the membranes at levels as low as 0.5 membrane mol%. Retinoic acid influenced permeability more than did retinol for each of the solutes tested. 2. Retinol and retinoic acid both decreased the electrical resistance of egg lecithin-planar bimolecular lipid membranes from 0.5 to 8 membrane mol%. Retinoic acid effected a larger change than did retinol. 3. Retinol and retinoic acid increased the permeability of dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine liposomes to water at 1.0 and 3.0 membrane mol%. A larger effect on water permeability was measured for retinoic acid than for retinol. 4. Retinol and retinoic acid at 1.0 and 3.0 membrane mol% were shown to lower the phase-transition temperature of liposomes composed of dimyristoylphosphatidylcholine or dipalmitoylphosphatidylcholine. Phase-transition temperatures were monitored by abrupt changes in water permeability and liposome size associated with the transition. Retinoic acid lowered the phase-transition temperature of dimyristoylphosphatidylcholine liposomes more than did retinol, while both retinoids had almost the same effect on dipalmitoylphosphatidylcholine liposomes.

Dimyristoylphosphatidylcholine↗
PubMed1981

Primordial transport of sugars and amino acids via Schiff bases.

Experimental support is given for a model concerning the origin of a primordial transport system. The model is based on the facilitated diffusion of amino acids stimulated by aliphatic aldehyde carriers and sugars stimulated by aliphatic amine carriers. The lipid-soluble diffusing species is the Schiff base. The possible role of this simple transport system in the origin of an early protocell is discussed.

Amino Acids↗
PubMed1980

Facilitated diffusion as a method for selective accumulation of materials from the primordial oceans by a lipid-vesicle protocell.

A model is proposed for the selective accumulation of amino acids, sugars, nucleotides, cations and protons from the primordial oceans into a lipid vesicle type of protocell. The model is built on facilitated diffusion using simple, primordial, lipid-soluble carriers. The advantages a lipid vesicle protocell would have had over the other potential types of protocells are discussed.

Amino Acids↗