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Ion Permeation and Block of P2X2 Purinoceptors: Single Channel Recordings
Authors:S Ding  F Sachs
Institution:(1) Department of Chemical Engineering, State University of New York at Buffalo, Buffalo, NY 14214, USA, US;(2) Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214, USA, US
Abstract:P2X2 purinoceptors are cation-selective channels activated by ATP and its analogues. Using single channel measurements we studied the channel's selectivity for the alkali metal ions and organic monovalent cations NMDG+, Tris+, TMA+, and TEA+. The selectivity sequence for currents carried by alkali metal ions is: K+ > Rb+ > Cs+ > Na+ > Li+, which is Eisenman sequence IV. This is different from the mobility sequence of the ions in free solution suggesting there is weak interaction between the ions and the channel interior. The relative conductance for alkali ions increases linearly in relation to the Stokes radius. The organic ions NMDG+, Tris+, TMA+ and TEA+ were virtually impermeant. The divalent ions (Mn2+, Mg2+, Ca2+ and Ba2+) induced a fast block visible as a reduction in amplitude of the unitary currents. Using a single-site binding model, the divalent ions exhibited an equilibrium affinity sequence of Mn2+ > Mg2+ > Ca2+ > Ba2+. Received: 3 May 1999/Revised: 23 August 1999
Keywords:: ATP —  Cations —  Patch-clamp —  Single channel
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