Ion permeation and block of P2X(2) purinoceptors: single channel recordings.
P2X(2) 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 (Mn(2+), Mg(2+), Ca(2+) and Ba(2+)) 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 Mn(2+) > Mg(2+) > Ca(2+) > Ba(2+).
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Department of Chemical Engineering, State University of New York at Buffalo, Buffalo, NY 14214, USA.
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D000255:Adenosine Triphosphate / Q000378:metabolism; D002460:Cell Line; D002586:Cesium / Q000378:metabolism; D004594:Electrophysiology; D006801:Humans; D008094:Lithium / Q000378:metabolism; D008536:Meglumine / Q000378:metabolism; D008672:Metals, Alkali / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D018048:Receptors, Purinergic P2 / Q000502:physiology*; D058476:Receptors, Purinergic P2X2; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013757:Tetraethylammonium Compounds / Q000378:metabolism; D014325:Tromethamine / Q000378:metabolism
D008672:Metals, Alkali; C546401:P2RX2 protein, human; D000644:Quaternary Ammonium Compounds; D018048:Receptors, Purinergic P2; D058476:Receptors, Purinergic P2X2; D013757:Tetraethylammonium Compounds; D014325:Tromethamine; D002586:Cesium; D008536:Meglumine; D000255:Adenosine Triphosphate; D008094:Lithium; D012964:Sodium; C027917:tetramethylammonium; D012413:Rubidium; D011188:Potassium