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Properties and modulation of alpha human atrial natriuretic peptide (α-hANP)-formed ion channels

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Using the lipid bilayer technique we have optimized recording conditions and confirmed that alpha human atrial natriuretic peptide [α-hANP(1–28)] forms single ion channels. The single channel currents recorded in 250/50 mM KCl cis/trans chambers show that the ANP-formed channels were heterogeneous, and differed in their conductance, kinetic, and pharmacological properties. The ANP-formed single channels were grouped as: (i) H2O2- and Ba2+-sensitive channel with fast kinetics; the nonlinear current-voltage (I-V) relationship of this channel had a reversal potential (Erev) of –28.2 mV, which is close to the equilibrium potential for K+ (EK = –35 mV) and a maximal slope conductance (gmax) of 68 pS at positive potentials. Sequential ionic substitution (KCl, K gluconate and choline Cl) of the cis solution suggests that the current was carried by cations. The fast channel had three modes (spike mode, burst mode, and open mode) that differed in their kinetics but not in their conductance properties. (ii) A large conductance channel possessing several subconductance levels that showed time-dependent inactivation at positive and negative membrane potentials (Vm). The inactivation ratio of the current at the end of the voltage step (I ss) to the initial current (I i) activated immediately after the voltage step, (I ss/I i), was voltage dependent and described by a bell-shaped curve. The maximal current-voltage (I-V) relationship of this channel, which had an Erev of +17.2 mV, was nonlinear and the value of gmax was 273 pS at negative voltages. (iii) A transiently-activated channel: the nonlinear I-V relationship of this channel had an Erev of –29.8 mV and the value of gmax was 160 pS at positive voltages. We propose that the voltage-dependence of the ionic currents and the kinetic parameters of these channel types indicate that if they were formed in vivo and activated by cytosolic factors they could change the membrane potential and the electrolyte homeostasis of the cell.Key words: natriuretic peptides, channel forming peptides, heterogeneous channels, signal transduction.

La technique de bicouche lipidique nous a permis d'optimiser nes conditions d'enregistrement et de confirmer que l'αANPh-(1–28) forme des canaux ioniques individuels. Les courants des canaux individuels dans 250/50 mM de KCl cis/trans montrent que les canaux formés par l'ANP étaient hétérogènes, montrant des différences au niveau de la conductance, de la cinétique et de la pharmacologie. Les canaux individuels formés par l'ANP ont été classés comme suit : (i) un canal sensible à l'H2O2 et au Ba2+, qui avait une cinétique rapide. La relation courant-tension (I-V) non linéaire de ce canal avait un potentiel d'inversion (Einv) de –28, 2 mV, qui est proche du potentiel d'équilibre de K+ (EK = –35 mV), et une conductance maximale (gmax) de 68 pS aux potentiels positifs. La substitution ionique séquentielle (KCl, K gluconate et choline Cl) de la solution cis donne à penser que le courant était transporté par des cations. La canal rapide avait trois modes (pointe, bouffée et ouverture), qui avaient des propriétés distinctes sur le plan de la cinétique mais similaires sur celui de la conductance; (ii) un canal de grande conductance qui avait plusieurs niveaux de sous-conductance et qui montrait une inactivation dépendante du temps aux potentiels de membrane (Vm) positifs et négatifs. Le rapport d'inactivation (I ss/I i) du courant à la fin de l'échelon de tension (I ss) au courant initial (I i) activé immédiatement après l'échelon de tension était dépendant de la tension et décrit par une courbe en cloche. La relation courant-tension (I-V) maximale de ce canal, qui avait un Einv de +17,2 mV, était non linéaire, et la valeur de gmax était de 273 pS aux tensions négatives; et (iii) un canal activé de manière transitoire. La relation I-V non linéaire de ce canal avait un Einv de 29,8 mV, et la valeur de gmax était 160 pS aux tensions positives. Ainsi, la dépendance
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Keywords: channel forming peptides; heterogeneous channels; natriuretic peptides; signal transduction

Document Type: Research Article

Publication date: August 1, 2001

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