The tetrodotoxin-resistant sodium channel Na(V)1.8/SNS is expressed exclusively in sensory neurons and appears to have an important role in pain pathways. Unlike other sodium channels, Na(V)1.8 is poorly expressed in cell lines even in the presence of accessory beta-subunits. Here we identify annexin II light chain (p11) as a regulatory factor that facilitates the expression of Na(V)1.8. p11 binds directly to the amino terminus of Na(V)1.8 and promotes the translocation of Na(V)1.8 to the plasma membrane, producing functional channels. The endogenous Na(V)1.8 current in sensory neurons is inhibited by antisense downregulation of p11 expression. Because direct association with p11 is required for functional expression of Na(V)1.8, disrupting this interaction may be a useful new approach to downregulating Na(V)1.8 and effecting analgesia.

The underlying mechanism for nerve growth factor (NGF) evoked pain and long-lasting mechanical hyperalgesia remains poorly understood. Using intrathecal antisense against the NGF receptor, receptor tyrosine kinase (TrkA), we found NGF to act at the primary afferent nociceptor directly in the Sprague-Dawley rat. Inhibitors of the three major pathways for TrkA receptor signalling, extracellular signal-related kinase (ERK)/mitogen-activated protein kinase kinase (MEK) (ERK/MEK), phosphatidylinositol 3-kinase (PI3K), and phospholipase Cgamma (PLCgamma) all attenuate NGF-induced hyperalgesia. Although inhibitors of kinases downstream of PI3K and PLCgamma[glycogen synthetase kinase 3 (GSK3), calmodulin-dependent protein kinase II (CAMII-K) or protein kinase C (PKC)] do not reduce mechanical hyperalgesia, hyperalgesia induced by activation of PI3K was blocked by ERK/MEK inhibitors, suggesting cross-talk from the PI3K to the ERK/MEK signalling pathway. As integrins have been shown to modulate epinephrine and prostaglandin E(2)-induced hyperalgesia, we also evaluated a role for integrins in NGF-induced mechanical hyperalgesia using beta(1)-integrin-specific antisense or antibodies.

We recently reported that hyperalgesia induced by the inflammatory mediator prostaglandin E(2) (PGE(2)) requires intact alpha1, alpha3 and beta1 integrin subunit function, whereas epinephrine-induced hyperalgesia depends on alpha5 and beta1. PGE(2)-induced hyperalgesia is mediated by protein kinase A (PKA), while epinephrine-induced hyperalgesia is mediated by a combination of PKA, protein kinase Cepsilon (PKCepsilon) and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK). We hypothesized that inflammatory mediator-induced hyperalgesia involves specific interactions between different subsets of integrin subunits and particular second messenger species. In the present study, function-blocking anti-integrin antibodies and antisense oligodeoxynucleotides were used to elucidate these interactions in rat. Hyperalgesia produced by an activator of adenylate cyclase (forskolin) depended on alpha1, alpha3 and beta1 integrins. However, hyperalgesia induced by activation of the cascade at a point farther downstream (by cAMP analog or PKA catalytic subunit) was independent of any integrins tested. In contrast, hyperalgesia induced by a specific PKCepsilon agonist depended only on alpha5 and beta1 integrins. Hyperalgesia induced by agonism of MAPK/ERK depended on all four integrin subunits tested (alpha1, alpha3, alpha5 and beta1). Finally, disruption of lipid rafts antagonized hyperalgesia induced by PGE(2) and by forskolin, but not that induced by epinephrine. Furthermore, alpha1 integrin, but not alpha5, was present in detergent-resistant membrane fractions (which retain lipid raft components). These observations suggest that integrins play a critical role in inflammatory pain by interacting with components of second messenger cascades that mediate inflammatory hyperalgesia, and that such interaction with the PGE(2)-activated pathway may be organized by lipid rafts.