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 P2X3 receptors to transduce
pain. To understand whether the CGRP action involves
P2X3 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 P2X3 receptors, acute application of CGRP did not change
P2X3 receptor function. Nevertheless, after 1 h of CGRP treatment, strong enhancement of the amplitude of
P2X3 receptor currents was observed together with accelerated recovery from desensitization. Receptor upregulation persisted up to 10 h (despite CGRP washout), was accompanied by increased P2X3 gene transcription, and was fully prevented by the CGRP antagonist CGRP(8-37). Surface biotinylation showed CGRP augmented
P2X3 receptor expression, consistent with confocal microscopy data indicating enhanced P2X3 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 P2X3 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.