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-P2x₇. In this study, we investigated the electrophysiological and pharmacological properties of rat P2x₁-P2x₄currents 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 P2x ₃ 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 P2X₂or P2X₃receptor-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.