Abstract

Human P2X 7 receptors were expressed in Xenopus laevis oocytes and single channels were recorded using the patch-clamp technique in the outside-out configuration. ATP 4− evoked two types of P2X 7 receptor-mediated single channel currents characterized by short-lived and long-lived openings. The short- and long-lasting open states had mean open times of ∼5 and ∼20 ms and slope conductances near −60 mV of 9 and 13 pS, respectively. The open probabilities of the short and long openings were strongly [ATP 4−]-dependent with EC 50 values of ∼0.3 mM and ∼0.1 mM ATP 4−, respectively. The channel kinetics did not change significantly during sustained P2X 7 receptor activation for several minutes, as was also observed in recordings in the cell-attached patch-clamp configuration. Activation and deactivation of the short openings followed exponential time courses with time constants in the range of 20 ms, and displayed a shallow [ATP 4−] dependence of the activation process. The kinetics of the short channel openings at negative membrane potentials fitted well to a linear C-C-C-O model with two ATP 4− binding steps at equal binding sites with a dissociation constant K d of 139 μM.

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