Artificial membrane excitability revisited and implications for the gating of voltage-dependent ion channels.
Excitability phenomena in planar lipid bilayers doped with alamethicin and protamines have been first described by Mueller and Rudin (Nature 217, 713-719, 1968). These properties are reinvestigated here with virtually solvent-free bilayers made of synthetic phospholipids doped with alamethicin charged component (Glu18) and protamine or other synthetic basic polypeptides. After retrieving the narrow set of experimental requisites allowing negative resistance and action potentials to develop, the potencies of different basic polypeptides were compared. Poly-arginines were found to be by far the most efficient. We also describe a transient increase of current amplitude upon addition of calcium that may reflect a lateral phase separation and conversely a gradual decrease of negative resistance due to tetrodotoxin, a potent sodium channel blocker. Functional modulations are correlated with conformational changes assayed in circular dichroism: alamethicin ellipticity in small unilamellar vesicles is markedly reduced upon protamine addition, only if the ionic strength is in the same low range that is compatible with regenerative conductance properties. These results are discussed in the framework of current models of ion channels gating.
Duclohier
H
H
Interactions Cellulaires et Moléculaires, UMR 6026 CNRS - Université de Rennes I, France. Herve.Duclohier@univ-rennes1.fr
Spach
G
G
D000200:Action Potentials; D000408:Alamethicin / Q000737:chemistry; D000595:Amino Acid Sequence; D000779:Anesthetics, Local / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002122:Calcium Chloride / Q000378:metabolism; D002942:Circular Dichroism; D004351:Drug Resistance; D004594:Electrophysiology; D007473:Ion Channels; D008051:Lipid Bilayers; D008567:Membranes, Artificial; D008969:Molecular Sequence Data; D010455:Peptides / Q000494:pharmacology; D011107:Polylysine / Q000494:pharmacology; D011189:Potassium Chloride / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013779:Tetrodotoxin / Q000494:pharmacology
D000779:Anesthetics, Local; D007473:Ion Channels; D008051:Lipid Bilayers; D008567:Membranes, Artificial; D010455:Peptides; D011107:Polylysine; C015462:polyarginine; D000408:Alamethicin; D013779:Tetrodotoxin; D011189:Potassium Chloride; D002122:Calcium Chloride; D002118:Calcium