Delayed upregulation of ATP P2X3 receptors of trigeminal sensory neurons by calcitonin gene-related peptide

Recent evidence indicates a key role for the neuropeptide calcitonin gene-related peptide ( CGRP) in migraine pain, as demonstrated by the strong analgesic action of CGRP receptor antagonists, although the mechanisms of this effect remain unclear. Most trigeminal nociceptive neurons releasing CGRP also express ATP-activated purinergic P2X(3) receptors to transduce pain. To understand whether the CGRP action involves P2X(3) receptor modulation, the model of trigeminal nociceptive neurons in culture was used to examine the long-term action of this peptide. Although 79% of CGRP-binding neurons expressed P2X(3) receptors, acute application of CGRP did not change P2X(3) receptor function. Nevertheless, after 1h of CGRP treatment, strong enhancement of the amplitude of P2X(3) receptor currents was observed together with accelerated recovery from desensitization. Receptor upregulation persisted up to 10 h ( despite CGRP washout), was accompanied by increased P2X(3) gene transcription, and was fully prevented by the CGRP antagonist CGRP(8-37). Surface biotinylation showed CGRP augmented P2X(3) receptor expression, consistent with confocal microscopy data indicating enhanced P2X(3) immunoreactivity beneath the neuronal membrane. These results suggest that CGRP stimulated trafficking of P2X3 receptors to the cell-surface membrane. Using pharmacological tools, we demonstrated that this effect of CGRP was dependent on protein kinase A and PKC activation and was prevented by the trafficking inhibitor brefeldin A. Capsaicin-sensitive TRPV1 vanilloid receptors were not upregulated. The present data demonstrate a new form of selective, slow upregulation of nociceptive P2X(3) receptors on trigeminal neurons by CGRP. This mechanism might contribute to pain sensitization and represents a model of neuronal plasticity in response to a migraine mediator.