RT Journal Article SR Electronic T1 Experimental Characterization and Mathematical Modeling of P2X7 Receptor Channel Gating JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 14213 OP 14224 DO 10.1523/JNEUROSCI.2390-10.2010 VO 30 IS 42 A1 Yan, Zonghe A1 Khadra, Anmar A1 Li, Shuo A1 Tomić, Melanija A1 Sherman, Arthur A1 Stojilkovic, Stanko S. YR 2010 UL http://www.jneurosci.org/content/30/42/14213.abstract AB The P2X7 receptor is a trimeric channel with three binding sites for ATP, but how the occupancy of these sites affects gating is still not understood. Here we show that naive receptors activated and deactivated monophasically at low and biphasically at higher agonist concentrations. Both phases of response were abolished by application of Az10606120, a P2X7R-specific antagonist. The slow secondary growth of current in the biphasic response coincided temporally with pore dilation. Repetitive stimulation with the same agonist concentration caused sensitization of receptors, which manifested as a progressive increase in the current amplitude, accompanied by a slower deactivation rate. Once a steady level of the secondary current was reached, responses at high agonist concentrations were no longer biphasic but monophasic. Sensitization of receptors was independent of Na+ and Ca2+ influx and ∼30 min washout was needed to reestablish the initial gating properties. T15E- and T15K-P2X7 mutants showed increased sensitivity for agonists, responded with monophasic currents at all agonist concentrations, activated immediately with dilated pores, and deactivated slowly. The complex pattern of gating exhibited by wild-type channels can be accounted for by a Markov state model that includes negative cooperativity of agonist binding to unsensitized receptors caused by the occupancy of one or two binding sites, opening of the channel pore to a low conductance state when two sites are bound, and sensitization with pore dilation to a high conductance state when three sites are occupied.