Kinetics of P2X7 receptor-operated single channels currents.
Human P2X7 receptors were expressed in Xenopus laevis oocytes and single channels were recorded using the patch-clamp technique in the outside-out configuration. ATP4- evoked two types of P2X7 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 approximately 5 and approximately 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 [ATP4-]-dependent with EC50 values of approximately 0.3 mM and approximately 0.1 mM ATP4-, respectively. The channel kinetics did not change significantly during sustained P2X7 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 [ATP4-] 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 ATP4- binding steps at equal binding sites with a dissociation constant Kd of 139 microM.
Riedel
T
T
Julius-Bernstein-Institute for Physiology, Martin-Luther-University Halle, Halle/Saale, Germany.
Lozinsky
I
I
Schmalzing
G
G
Markwardt
F
F
D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D003198:Computer Simulation; D015640:Ion Channel Gating / Q000502:physiology*; D007700:Kinetics; D008954:Models, Biological; D008956:Models, Chemical; D009865:Oocytes / Q000502:physiology*; D018048:Receptors, Purinergic P2 / Q000737:chemistry* / Q000502:physiology*; D058486:Receptors, Purinergic P2X7; D014982:Xenopus laevis
C546468:P2RX7 protein, human; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D000255:Adenosine Triphosphate