Purotoxin1 (PT-1) is a P2X3 selective inhibitor. This peptide was originally isolated from the Central Asian spider Geolycosa sp. It was shown to inhibit selectively P2X3 receptor channels at a 100 nM concentration. Studies were carried-out on cultured rat DRG neurons. Patch-clamp experiments did not show any inhibitory effect of PT-1 on voltage-gated channels (potentials range tested from -100 to 20 mV), neither on TRPV1 (after activation with 500 nM capsaicin). The selectivity of PT-1 for P2X3 was highlighted by activating this receptor with 10 µM ATP and 100 µM α, β Methylene-ATP. Indeed, unlike P2X3, P2X2 and heterodimer P2X2/3 are known to be not sensitive to such concentrations. Moreover, P2X3, P2X2, and P2X2/3 are the only known ATP-sensitive receptors expressed in plasma membranes of DRG neurons. So, the observed effect seems to be well related to a selective inhibition of P2X3. P2X3-mediated current was fully inhibited with 100 nM PT-1, making it the most potent and selective ligand for P2X3.

Therapeutic interest : pain

P2X3 receptors are known to be implicated in pain mechanisms. Behavioral experimentations carried-out on rat pain models using 0.5 nmol PT-1 injected intraplantar showed to reduce nociception. This anti-nociceptive effect is comparable to A-317491 compound (Abbott's drug) with an amount of almost 3 orders of magnitude lower.

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