Functional differences between ATP-gated Human and Rat P2X3 Receptors are caused by critical residues of the Intracellular C-Terminal Domain

ATP-activated P2X3 receptors of sensory ganglion neurons contribute to pain transduction and are involved in chronic pain signaling. Although highly homologous (97%) in rat and human species, it is unclear whether P2X3 receptors have identical function. Studying human and rat P2X3 receptors expressed in patch-clamped human embryonic kidney (HEK) cells, we investigated the role of non-conserved tyrosine residues in the C-terminal domain (rat tyrosine-393 and human tyrosine-376) as key determinants of receptor function. In comparison with rat P2X3 receptors, human P2X3 receptors were more expressed and produced larger responses with slower desensitization and faster recovery. In general, desensitization was closely related to peak current amplitude for rat and human receptors. Downsizing human receptor expression to the same level of the rat one still yielded larger responses retaining slower desensitization and faster recovery. Mutating phenylalanine-376 into tyrosine in the rat receptor did not change current amplitude; yet, it retarded desensitization onset, demonstrating how this residue was important to functionally link these two receptor states. Conversely, removing tyrosine from position 376 strongly down-regulated human receptor function. The different topology of tyrosine residues in the C-terminal domain has contrasting functional consequences and is sufficient to account for species-specific properties of this pain-transducing channel. 'Of Mice and Men'? A single amino acid in the pain-transducing P2X3 receptor structure can determine human or rat function. The reason why the human P2X3 receptor generates much larger responses than the homologous rat one was investigated. Changing the position of one tyrosine in the intracellular C-terminus converted the function of the human receptor to the rat one, and vice versa. Species-specific differences in P2X3 responses to harmful stimuli may be attributed to the location of a single tyrosine residue, which is modulated by intracellular kinases to determine the strength of pain signaling to the brain. © 2012 International Society for Neurochemistry.