This Article Full Text Full Text (PDF) Supplement All Versions of this Article: biophysj.106.091413v1 92/7/2377    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Riedel, T. Articles by Markwardt, F. Search for Related Content PubMed PubMed Citation Articles by Riedel, T. Articles by Markwardt, F.

Kinetics of P2X₇ Receptor-Operated Single Channels Currents

T. Riedel ^*, I. Lozinsky , G. Schmalzing  and F. Markwardt ^*

^* Julius-Bernstein-Institute for Physiology, Martin-Luther-University Halle, Halle/Saale, Germany; Department of Internal Medicine, University of Kentucky, Lexington, Kentucky; and RWTH Aachen University, Department of Molecular Pharmacology, Aachen, Germany

Correspondence: Address reprint requests to F. Markwardt, Tel.: 49-345-557-1390; E-mail: fritz.markwardt{at}medizin.uni-halle.de.

Human P2X₇ 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 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 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 EC₅₀ values of 0.3 mM and 0.1 mM ATP^4–, 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 [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.