Peripheral inflammation upregulates P2X receptor expression in satellite glial cells of mouse trigeminal ganglia: a calcium imaging study.

Satellite glial cells (SGCs) in sensory ganglia are altered structurally and biochemically as a result of nerve injury. Whereas there is ample evidence that P2 purinergic receptors in central glial cells are altered after injury, there is very little information on similar changes in SGCs, although it is well established that SGCs are endowed with P2 receptors. Using calcium imaging, we characterized changes in P2 receptors in SGCs from mouse trigeminal ganglia in short-term cultures. Seven days after the induction of submandibular inflammation with complete Freund's adjuvant, there was a marked increase in the sensitivity of SGCs to ATP, with the threshold of activation decreasing from 5 μM to 10 nM. A similar observation was made in the intact trigeminal ganglion after infra-orbital nerve axotomy. Using pharmacological tools, we investigated the receptor mechanisms underlying these changes in cultured SGCs. We found that in control tissues response to ATP was mediated by P2Y (metabotropic) receptors, whereas after inflammation the response was mediated predominantly by P2X (ionotropic) receptors. As the contribution of P2X1,3,6 receptors was excluded, and the sensitivity to a P2X7 agonist did not change after inflammation, it appears that after inflammation the responses to ATP are largely due to P2X2 and/or 5 receptors, with a possible contribution of P2X4 receptors. We conclude that inflammation induced a large increase in the sensitivity of SGCs to ATP, which involved a switch from P2Y to P2X receptors. We propose that the over 100-fold augmented sensitivity of SGCs to ATP after injury may contribute to chronic pain states.