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

Abstract

Using the lipid bilayer technique we have optimized recording conditions and confirmed that alpha human atrial natriuretic peptide [alpha-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) H202- 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 (Iss) to the initial current (Ii) activated immediately after the voltage step, (Iss/Ii), 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.