Block by extracellular Mg2+ of single human purinergic P2X(4) receptor channels expressed in human embryonic kidney cells

Single channel properties of human P2X(4) receptors expressed in human embr yonic kidney cells have been investigated by outside-out mode patch clamp r ecordings. P2X(4) channel activity was characterized by very fast kinetics. The current-voltage relationship was strongly non-linear at potentials <-1 00 mV. A slope conductance of approximate to 9 pS was estimated at the appr oximately linear part of the current-voltage relation (>-100 mV). External Mg2+ reversibly decreased the amplitude of ATP-evoked single channel curren ts in a concentration-dependent man ner but independent of the membrane pot ential. Additionally, extracellular Mg2+ shortened the mean open time where as the mean closed time was not affected. Thus, Mg2+ ions are proposed to i nhibit the function of human P2X(4) receptors by means of an open-channel b lock with a Mg2+ binding site at the exterior surface of the pore. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.