Effects of morphine preconditioning on TRPV1 sensitization and ERK1/2 phosphorylation induced by TGFβ1 in neurocytes

Myocardium ischemia-reperfusion injury (IRI) is the major cause of cardiac dysfunction. While intrathecal morphine preconditioning (MPC) can alleviate IRI in animal model, the molecular processes underlying IRI and MPC remain elusive. This study aims to test whether pretreatment with morphine can ameliorate the increased activity of transient receptor potential vanilloid 1 (TRPV1) induced by transforming growth beta1 (TGFβ1) in cultured dorsal root ganglion neurons as a model of the effects of cardiac ischemia on nociceptive primary afferent neurons.

To simulate the effect of MPC on dorsal root ganglia (DRG) neurons during myocardial IRI in vivo, the cells were pretreated with morphine for 10 min, followed by wash-out for 30 min before TGFβ1 was added. Afterwards, DRG neurons and N2a cells in all groups were stimulated by capsaicin, and the inward current induced by capsaicin were detected by whole-cell recording on DRG neurons; the expression of TRPV1, phosphorylated (p) TRPV1, ERK1/2, and pERK1/2 were detected by western blot in N2a cells.

In comparison with cells with normal culture, the inward current was enhanced of cells incubated with TGFβ1 (P < 0.05), and the relative expression of TRPV1, pTRPV1, and pERK1/2 was upregulated as well (P < 0.05); In comparison with cells incubated with TGFβ1, the inward current induced by capsaicin were decreased by pretreatment with morphine (P < 0.05), Moreover, the relative expression of TRPV1, pTRPV1, and pERK1/2 were also reduced by MPC (P < 0.05).

MPC inhibits TRPV1 sensitized by TGFβ1 in DRG cells, and the mechanism might be associated with the downregulation of pERK1/2 expression.