Experimental and modeling studies of desensitization of P2X3 receptors.
The function of ATP-activated P2X3 receptors involved in pain sensation is modulated by desensitization, a phenomenon poorly understood. The present study used patch-clamp recording from cultured rat or mouse sensory neurons and kinetic modeling to clarify the properties of P2X3 receptor desensitization. Two types of desensitization were observed, a fast process (t1/2 = 50 ms; 10 microM ATP) following the inward current evoked by micromolar agonist concentrations, and a slow process (t1/2 = 35 s; 10 nM ATP) that inhibited receptors without activating them. We termed the latter high-affinity desensitization (HAD). Recovery from fast desensitization or HAD was slow and agonist-dependent. When comparing several agonists, there was analogous ranking order for agonist potency, rate of desensitization and HAD effectiveness, with 2-methylthioadenosine triphosphate the strongest and beta,gamma-methylene-ATP the weakest. HAD was less developed with recombinant (ATP IC50 = 390 nM) than native P2X3 receptors (IC50 = 2.3 nM). HAD could also be induced by nanomolar ATP when receptors seemed to be nondesensitized, indicating that resting receptors could express high-affinity binding sites. Desensitization properties were well accounted for by a cyclic model in which receptors could be desensitized from either open or closed states. Recovery was assumed to be a multistate process with distinct kinetics dependent on the agonist-dependent dissociation rate from desensitized receptors. Thus, the combination of agonist-specific mechanisms such as desensitization onset, HAD, and resensitization could shape responsiveness of sensory neurons to P2X3 receptor agonists. By using subthreshold concentrations of an HAD-potent agonist, it might be possible to generate sustained inhibition of P2X3 receptors for controlling chronic pain.
Sokolova
Elena
E
International School for Advanced Studies, Via Beirut 4, 34104 Trieste, Italy.
Skorinkin
Andrei
A
Moiseev
Igor
I
Agrachev
Andrei
A
Nistri
Andrea
A
Giniatullin
Rashid
R
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008954:Models, Biological; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D018408:Patch-Clamp Techniques; D058910:Purinergic P2 Receptor Agonists; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000235:genetics / Q000502:physiology*; D058477:Receptors, Purinergic P2X3; D013873:Thionucleotides / Q000494:pharmacology
C546407:P2RX3 protein, human; C546409:P2rx3 protein, mouse; C546410:P2rx3 protein, rat; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; D058477:Receptors, Purinergic P2X3; D013873:Thionucleotides; C005147:5'-adenylyl (beta,gamma-methylene)diphosphonate; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; C008501:2-methylthio-ATP