Pharmacological and electrophysiological characterization of rat P2X currents
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Adenosine 5’-triphosphate (ATP) is an important extracellular signaling molecule which is involved in a variety of physiological responses in many different tissues and cell types, by acting at P2 receptors, either ionotropic (P2X) or G protein-coupled metabotropic receptors (P2Y). P2X receptors have seven isoforms designated as P2X₁-P2X_7. In this study, we investigated the electrophysiological and pharmacological properties of rat P2X₁-P2X₄ currents by using whole-cell patch clamp technique in a heterologous expression system. When ATP-induced currents were analyzed in human embryonic kidney (HEK293) cells following transient transfection of rat P2X₁-P2X₄, the currents showed different pharmacological and electrophysiological properties. ATP evoked inward currents with fast activation and fast desensitization in P2X₁- or P2X₃- expressing HEK293 cells, but in P2X₂- or P2X₄-expressing HEK293 cells, ATP evoked inward currents with slow activation and slow desensitization. While PPADS and suramin inhibited P2X₂ or P2X₃ receptor-mediated currents, they had little effects on P2X₄ receptor-mediated currents. Ivermectin potentiated and prolonged P2X₄ receptor-mediated currents, but did not affect P2X₂ or P2X₃ receptor-mediated currents. We suggest that distinct pharmacological and electrophysiological properties among P2X receptor subtypes would be a useful tool to determine expression patterns of P2X receptors in the nervous system including trigeminal sensory neurons and microglia.
Abstract
Adenosine 5’-triphosphate (ATP) is an important extracellular signaling molecule which is involved in a variety of physiological responses in many different tissues and cell types, by acting at P2 receptors, either ionotropic (P2X) or G protein-coupled metabotropic receptors (P2Y). P2X receptors have seven isoforms designated as P2X₁-P2X_7. In this study, we investigated the electrophysiological and pharmacological properties of rat P2X₁-P2X₄ currents by using whole-cell patch clamp technique in a heterologous expression system. When ATP-induced currents were analyzed in human embryonic kidney (HEK293) cells following transient transfection of rat P2X₁-P2X₄, the currents showed different pharmacological and electrophysiological properties. ATP evoked inward currents with fast activation and fast desensitization in P2X₁- or P2X₃- expressing HEK293 cells, but in P2X₂- or P2X₄-expressing HEK293 cells, ATP evoked inward currents with slow activation and slow desensitization. While PPADS and suramin inhibited P2X₂ or P2X₃ receptor-mediated currents, they had little effects on P2X₄ receptor-mediated currents. Ivermectin potentiated and prolonged P2X₄ receptor-mediated currents, but did not affect P2X₂ or P2X₃ receptor-mediated currents. We suggest that distinct pharmacological and electrophysiological properties among P2X receptor subtypes would be a useful tool to determine expression patterns of P2X receptors in the nervous system including trigeminal sensory neurons and microglia.
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