A hydrophobic residue in position 15 of the rP2X3 receptor slows desensitization and reveals properties beneficial for pharmacological analysis and high-throughput screening

The homotrimeric P2X3 subtype, one of the seven members of the ATP-gated P2X receptor family, plays a role in sensory neurotransmission, including nociception. To overcome the bias resulting from fast desensitization of the P2X3 receptor in dose–response analyses, a non-desensitizing P2X2-X3 receptor chimera has been repeatedly used as a surrogate for the P2X3 receptor for functional analysis. Here, we show that only three of the P2X2-specific amino acid residues of the P2X2-X3 chimera, 19P21V22I, are needed to confer a slowly desensitizing phenotype to the P2X3 receptor. The strongest delay in desensitization of the P2X3 receptor by a single residue was observed when 15Ser was replaced by Val or another hydrophobic residue. Pharmacologically, the S15V-rP2X3 mutant behaved similarly to the wt-P2X3 receptor. Analysis of the S15V-rP2X3 receptor in 1321N1 astrocytoma cells by a common calcium-imaging-based assay showed 10-fold higher calcium transients relative to those of the wt-rP2X3 receptor. The S15V-rP2X3 cell line enabled reliable analysis of antagonistic potencies and correctly reported the mechanism of action of the P2X3 receptor antagonists A-317491 and TNP-ATP by a calcium-imaging assay. Together, these data suggest that the S15V-rP2X3 mutant may be suitable not only for automated fluorescence-based screening of molecule libraries for identification of lead compounds but also for facilitated pharmacological characterization of specific P2X3 receptor ligands. We suggest that the mechanism of desensitization of the P2X3 receptor may involve the movement of an N-terminal inactivation particle, in analogy to the “hinged-lid“ or “ball and chain” mechanisms of voltage-gated NaV and Shaker KV channels, respectively. •Three N-terminal P2X2-specific residues strongly retard P2X3 receptor desensitization.•Most of the delayed desensitization of the P2X3 triple mutant can be assigned to S15V.•Other hydrophobic substitutions of 15S also slow desensitization of the P2X3.•S15V-rP2X3 was pharmacologically indistinguishable from the wt-P2X3 receptor.•A S15V-rP2X3 1321N1 cell line facilitated automated screening of P2X3 antagonists.