Inhibitory effect of cochinchinenin B on capsaicin-activated responses in rat dorsal root ganglion neurons

Vanilloid receptor 1 (VR1) is a noxious receptor and a novel target for pain therapy. Cochinchinenin B (6-hydroxy-7-methoxy-3-(4′-hydroxybenzyl) chromone; CB) is one of the small-molecular components from the flavonoids of Dragon's Blood, a well-known herbal medicine to treat various types of pain. Using whole-cell patch clamp technique, we found that capsaicin (CAP)-activated currents (ICAP) was inhibited by CB with an IC50 of 0.92 mM in acutely isolated rat dorsal root ganglion (DRG) neurons. The inhibition was reversible and not competitive. We also found that the inhibition was neither voltage- nor agonist-dependent. The bind site was on the extracellular part of the channel since intracellular application of CB did not alter the inhibition effect on ICAP. In addition, CB inhibited CAP-evoked depolarization under current-clamp condition. Our findings indicate that CB may be a candidate in developing new analgesic drugs targeting the VR1 receptor.