Quantification of TRPV1 protein levels in rat tissues to understand its physiological roles.

Transient receptor potential subfamily V, member 1 (TRPV1) is a nonselective cation channel expressed in both the peripheral and central nervous systems (CNS). TRPV1 protein levels in rat tissues were determined under normal and pain states using enzyme-linked immunosorbent assay. In naive rats, brain TRPV1 protein concentrations ranged from 1.5 to 4 ng/mg in hippocampus, cortex, hypothalamus, and cerebellum. Rat spinal cord TRPV1 protein levels were 40-50 ng/mg in L1-L5 of the lumbar regions, but increased to 97 ± 9.3 ng/mg toward the end of the lumbar region (L6-S1). In the complete Freund's adjuvant (CFA)-induced inflammatory pain model, TRPV1 protein level significantly increased on both the contralateral (36.5 %, p < 0.05) and ipsilateral (31.4 %, p < 0.05) L4-L6 dorsal root ganglia (DRG). TRPV1 protein levels also increased 33.3 % (p < 0.05) on the ipsilateral sciatic nerve, but no significant change in the lumbar spinal cord of CFA rats. In the monoiodoacetate-induced rat knee joint pain model, TRPV1 protein level was significantly reduced in the ipsilateral L3-L5 DRG (33.3 %, p < 0.01), no significant difference was detected in the lumbar region of the spinal cord. Quantitative determination of TRPV1 protein levels may help to elucidate the TRPV1 physiological roles and regulatory mechanisms in various pain states.