Emodin is a principle ingredient isolated from rhubarb rhizome, which is commonly used for
constipation or
pain-related diseases in
traditional Chinese medicine (TCM) practice. The transient receptor potential vanilloid 1
ion channel proteins (TRPV1) are abundantly expressed in the peripheral sensory neurons and are assumed to act as a kind of nociceptor involved in the perception of
pain and development of
hyperalgesia. The aim of this study was to further unravel the
analgesic mechanisms of rhubarb through investigating the effects of its main constitutive ingredient
emodin on the expression of TRPV1
mRNA as well as on its
calcium- mediating functions in vitro. The primary DRG neurons with a high purity and viability were obtained, and the TRPV1
mRNA expression levels were examined by using real-time RT-PCR and the elevated amplitudes of intracellular [Ca(2+)]i in the DRG neurons evoked by TRPV1 agonist
capsaicin were examined by confocal microscopy. The results showed that
emodin could significantly down-regulate both the
mRNA expression of TRPV1 and the
capsaicin-evoked intracellular fluorescent intensity in the DRG neurons under both 37 degrees C and 39 degrees C in vitro. Concomitantly, all of the changes induced by
emodin could not be blocked by pretreatment of the primary neurons with
capsazepine, an antagonist of TRPV1. In conclusion, we established that the
mRNA expression level of TRPV1 and its
calcium-mediating function in naive DRG neurons could be down-regulated by
emodin through perhaps the non-TRPV1 channel pathways, and this might be the molecular mechanisms for rhubarb to inhibit
hyperalgesia induced by inflammatory stimuli.