Pulse radiolysis at planar lipid membranes doped with ion carriers or pore formers

doi:10.1016/0005-2736(84)90179-2

Biochimica et Biophysica Acta (BBA) - Biomembranes

Volume 775, Issue 2, 22 August 1984, Pages 265-268

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Abstract

The effect of 14 MeV electrons on ion transport through planar lipid membranes was investigated. The membranes were formed in the presence of well defined ion carriers or pore forming substances. In the presence of the ion carriers valinomycin or nonactin or in the presence of the pore formers nystatin or amphotericin B, irradiation produced a transient increase of the membrane conductance followed by a long lasting decrease. The effects are interpreted on the basis of a time-dependent chemical modification of the membrane structure caused by exposure to high energy radiation. The pore former gramicidin A shows an exponential inactivation with increasing dose. At pH 3 and in the presence of oxygen the pore is highly sensitive to radiation ( $D_{37} ≈ 10 Gy$ ) whereas at pH 9.5 a considerably lower radiation sensitivity ( $D_{37} ≈ 1000 Gy$ ), was found. In the absence of oxygen, gramicidin A is virtually insensitive to irradiation. This is considered an evidence that the inactivation of this ion channel is primarily caused by the perhydroxyl radical HO₂.

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Cited by (11)

Sensitized Photoinactivation of Gramicidin Channels: Technique and Applications
2005, Advances in Planar Lipid Bilayers and Liposomes
Citation Excerpt :
The discovery of photodynamic inactivation of gramicidin channels was linked to earlier studies of gramicidin A inactivation by ionizing radiation performed by Stark and coworkers ([1] and references therein). According to the results obtained, the radiation damage to gramicidin channels was mediated by ROS, in particular oxygen radicals [2–4]. By that time ROS were implicated also in membrane photomodification leading to cell killing caused by photosensitization ([5–10] see also references therein), the phenomenon underlying photodynamic therapy of tumors [11–16].
This review is devoted to the analysis of sensitized photoinactivation of ionic channels formed by gramicidin A in bilayer lipid membranes. There has been a long way from the discovery of this phenomenon in 1992 and the first ideas concerning its mechanism to its application for studying the interaction of different agents with modified gramicidins. Measuring transmembrane current transients after a flash of visible light in the presence of a photosensitizer represents a very convenient method of determining rate constants of gramicidin channel formation and dissociation. In the present review, both the advantages and the drawbacks of the photoinactivation technique are compared with those of the conventional approaches, such as single-channel measurements, the voltage-jump technique, and the noise power spectrum analysis. A study of the interaction of charged gramicidin analogues with polyelectrolytes by using the sensitized photoinactivation procedure is described here in detail to demonstrate the wide potencies of this method. In addition, it is shown that the gramicidin channel photoinactivation can also be used for screening of new potent photosensitizers, and for the search of scavengers effectively protecting membrane systems from the attack of reactive oxygen species.
The interaction of phthalocyanine with planar lipid bilayers. Photodynamic inactivation of gramicidin channels
1993, FEBS Letters
The effect of phthalocyanines, the potent photodynamic sensitizers, on the electric properties of the bilayer lipid membrane (BLM) is studied. It is shown, that tetrasulfonated, as well as trisulfonated, aluminium phthalocyanine do not alter the conductance of BLM, but elicit certain changes in the boundary potential difference, which points in favor of dye adsorption on BLM. Under the conditions of intense visible light irradiation, the phthalocyanines cause an increase in the conductance, resulting in the irreversible breakdown of BLM, formed from soy bean phosphati-dylcholine, but fail to change the conductance of BLM, formed from diphytanoilphosphatidylcholine. The phthalocyanine-sensitized inactivation of gramicidin channels incorporated into BLM is observed under the conditions of weak visible light irradiation using an He-Ne laser. The photodynamic blockage of model ionic channels is considerably suppressed after oxygen depletion. The phenomenon consists of a marked reduction of a number of open channels, probably due to photomodification of tryptophan residues, essential for gramicidin functioning. The mechanism of the channel inactivation, involving the photosensitized reaction of the II type, and the relevance to the interaction of sensitizers with biomembranes, is discussed.
The effect of ionizing radiation on lipid membranes
1991, BBA - Reviews on Biomembranes
Radiation inactivation of ion channels formed by gramicidin A. Protection by lipid double bonds and by α-tocopherol
1991, BBA - Biomembranes
The conductance induced by the channel-forming peptide gramicidin A in lipid membranes is reduced by many orders of magnitude on exposure of the membrane and its aqueous environment to ionizing radiation. This results from an interaction of free radicals of water radiolysis with the tryptophan residues of gramicidin A. The sensitivity of the ion channels towards irradiation is strongly reduced in the presence of either vitamin E or of highly unsaturated lipids. An increase of the D₃₇ dose up to a factor of 50 was found. The phenomena are interpreted via a reduction of the effective concentration of free radicals (such as OH) in the membrane by reaction with unsaturated fatty acid residues or with vitamin E.
Radiolysis and photolysis of ion channels formed by analogues of gramicidin A with a varying number of tryptophan residues
1989, BBA - Biomembranes
The ion channels formed by gramicidin A in planar lipid membranes may be inactivated by application of comparatively small doses of ionizing radiation (radiolysis) or by UV irradiation (photolysis). Both effects are reduced by several orders of magnitude, if the four tryptophan residues of gramicidin A are replaced by phenylalanines, tyrosines or by naphthylalanines. The present communication reports on the influence of a varying number of tryptophan residues per gramicidin monomer. The sensitivity of the channels towards photolysis was found to be roughly proportional to the number of tryptophans. The channels show complete inactivation in the presence of only one tryptophan residue per monomer. In the case of radiolysis, complete inactivation was observed for normal gramicidin A only. For those analogues having only one (or two) tryptophan residues per monomer, part of the initial conductance was found to be insensitive towards irradiation. As only small changes of the single-channel characteristics (amplitude and life-time) were observed, the radiation-sensitive part was mainly attributed to a reduced rate of channel formation. It is interpreted as a radiation-induced inhibition of the aggregation of gramicidin dimers. Aggregation, favoured by Trp-Trp contacts, is thought to represent an essential step for channel opening.
NMR analysis of the ultraviolet photolytic behavior of several tryptophan-rich growth hormone releasing peptides
1997, Biospectroscopy

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BBA reportPulse radiolysis at planar lipid membranes doped with ion carriers or pore formers

Abstract

Biochim. Biophys. Acta

Biochim. Biophys. Acta

Fundamentals of Radiobiology

Cellular Radiobiology

Biomembranes

Q. Rev. Biophys.

BBA report
Pulse radiolysis at planar lipid membranes doped with ion carriers or pore formers