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H Duclohier

Publications and source records attributed to H Duclohier.

48 records · Page 3Linked to original sources
PubMed1989

Antimicrobial peptide magainin I from Xenopus skin forms anion-permeable channels in planar lipid bilayers.

The ionophore properties of magainin I, an antimicrobial and amphipathic peptide from the skin of Xenopus, were investigated in planar lipid bilayers. Circular dichroism studies, performed comparatively with alamethicin, in small or large unilamellar phospholipidic vesicles, point to a smaller proportion of alpha-helical conformation in membranes. A weakly voltage-dependent macroscopic conductance which is anion-selective is developed when using large aqueous peptide concentration with lipid bilayer under high voltages. Single-channel experiments revealed two main conductance levels occurring independently in separate trials. Pre-aggregates lying on the membrane surface at rest and drawn into the bilayer upon voltage application are assumed to account for this behaviour contrasting with the classical multistates displayed by alamethicin.

Amino Acid Sequence↗
PubMed1988

Intracellular pH change does not appear as a prerequisite for triggering activation of Barnea candida (Mollusca, Pelecypoda) oocytes.

Barnea candida oocytes, exposed to excess KCl, ammonia, or digitonin, exhibit germinal vesicle breakdown (GVBD) and reinitiate meiosis, at least up to first polar body extrusion. While we confirm that KCl- but not ammonia-induced activation required external calcium, our findings that digitonin is effective at any pH from 6 to 8, in the presence of calcium, while the phorbol ester TPA and diacylglycerol fail to reinitiate meiosis, strongly suggests calcium as the main trigger for this process. Preliminary experiments using the fluorescent probes fluorescein diacetate and Quin 2/AM show, moreover, that KCl and ammonia produce both an intracellular calcium surge (30 nM) and a slight alkalinization of the intracellular cytoplasm from 7.84 to 8.05.

Animals↗
PubMed1988

Orientation of the tryptophans responsible for the photoinactivation of nerve sodium channels.

UV irradiation of squid giant axons at wavelengths of 280 or 290 nm produces nearly the same rate of irreversible decrease of sodium currents. The rate of photodeactivation is unaffected by extensive removal of axoplasm with pronase, and it is independent of temperature in the range 5 degrees to 20 degrees C. The photochemical effect appears to be all or nothing. It does not alter the time course and the voltage dependence for activation and inactivation of the residual currents. Similar deactivation rates were produced by irradiations of the same intensity, but linearly polarized either parallel or perpendicular to the axon. The efficiency of the deactivation process is close to that expected if it was caused by the photooxidation of a single tryptophan residue per sodium channel. Owing to the geometry of the preparation the lack of polarization asymmetry suggests that this residue assumes nearly random (or pseudo-random) orientation in the three-dimensional structure of the sodium channel corresponding to the closed state.

Animals↗
PubMed1988

Ionophore properties of a synthetic alpha-helical transmembrane fragment of the mitochondrial H+ ATP synthetase of Saccharomyces cerevisiae. Comparison with alamethicin.

A 22-amino acid polypeptide was synthesized to model the central transmembrane segment of subunit 8 of the H+ ATP synthetase of Saccharomyces cerevisiae and to test ionophore properties. Solid-phase synthesis was conducted on benzhydrilamino resin, and purification followed by high pressure liquid chromatography allowed the isolation of the pure product whose NH2 terminal was acetylated and whose molecular weight determined by Fast Atomic Bombardment was the expected 2,666. The infrared spectrum of this peptide in the solid state reveals a fully alpha-helical conformation, whereas in low dielectric constant solvents the alpha-helical content is 60%, as determined by circular dichroism studies. Macroscopic current-voltage curves displayed by different planar lipid bilayers (monomyristoleoyl-glycerol and phosphatidylethanolamine) doped with this peptide suggest a weakly voltage-dependent conductance. Only one conductance level is observed in any given single-channel conductance experiment. However, a series of experiments shows a distribution of conductance states, most often 440 or 3,000 pS, and occasionally 80, 1,200, or 6,500 pS. This behavior contrasts with the usual behavior of alamethicin, chosen as a model of "aggregating-helices" ionophore and whose conductance fluctuates continually between substates, through uptake and release of monomers. Nevertheless, alamethicin too can display, under certain conditions, long-lived and mono-level conductance states similar to those reported here for the newly synthesized peptide. These properties could possibly be explained by the formation of large domains of helical rods with a set of allowed and independent ionic pathways.

Alamethicin↗
PubMed1987

Voltage-dependent and multi-state ionic channels induced by trichorzianines, anti-fungal peptides related to alamethicin.

The ionophore properties of two peptaibols of the trichorzianine family have been investigated in planar lipid bilayers and compared to those of alamethicin. Macroscopic conductance experiments reveal voltage-dependent channels only in the thinnest membranes and a greater efficiency of the neutral analog. In single-channel experiments, a multi-state behaviour, consistent with the usual barrel-stave model, is disclosed but the discrete current fluctuations are much more rapid than for alamethicin. The results indicate a stringent requirement for the helix length/bilayer thickness match in agreement with a previous model and suggest the design of new synthetic peptides.

Alamethicin↗
PubMed1987

Single chloride-permeable channels of large conductance in cultured cardiac cells of new-born rats.

Large conductance channels were observed in the membrane of cultured cardiac cells of newborn rats studied with the patch-clamp technique in cell-attached and inside-out configurations. These channels were observed in approximately equal to 4% of the patches. In the cell-attached configuration they exhibited outward rectification and partial inactivation. In the inside-out configuration no rectification occurred but inactivation was present, mainly during hyperpolarizations. Two channels with large single unit conductances (400-450 pS) and one with a smaller conductance (200-250 pS) were frequently observed in the same patch. The two large channels generally had different kinetics. Under steady-state conditions the opening probability of the faster channel appeared to be voltage-independent. The slower channel was activated by depolarization. In asymmetrical solutions the permeability ratios PNa/PCl were 0.03 and 0.24 for the larger and smaller channels, respectively; corresponding values for PBa/PCl were 0.04 and 0.09. It is proposed that in cardiac membranes the chloride permeability system is composed of widely dispersed microclusters forming grouped channels of different types and sizes.

Animals↗
PubMed1983

[Relation between the axonal membrane microfluidity and excitability].

The olfactory nerve of the garfish, the rabbit vagus nerve and the sciatic nerve of the frog labelled with pyrene or triethylammonium-butyl-pyrene show during the action potential a transient decrease in the Ie/Im ratio which suggest a small transient decrease in nerve membrane fluidity.

Animals↗
PubMed1979

Temperature dependence of the fluorescence of pyrene labeled crab nerve membranes.

A method, using albumin-pyrene complexes, has been developed for labeling, in a controlled manner, crab leg nerves whose excitability was preserved. The excimer-to-monomer fluorescence intensity ratio of pyrene, embedded in nerve membrane lipids and in their crude lipid extracts, is a fluidity parameter which displayed the following features with temperatures. a--a temperature-dependent increase of fluidity b--three breaks (6 degrees, 19 degrees and 37 degrees C) in the physiological medium c--In Ca++-depleted sea water, the 37 degrees characteristic temperature vanished. These breaks may reflect some lateral phase separations of the lipid components of nerve membranes. The calcium dependent temperature break may involve a segregation of acidic phospholipids while the other two breaks (6 degrees and 19 degrees C) may be due to neutral lipids phase separation. The relationship of these findings to nerve function is discussed.

Animals↗