Exp Neurobiol.  2012 Jun;21(2):75-82. 10.5607/en.2012.21.2.75.

Capsaicin Blocks the Hyperpolarization-Activated Inward Currents via TRPV1 in the Rat Dorsal Root Ganglion Neurons

Affiliations
  • 1Department of Physiology and Biophysics, Inha University College of Medicine, Incheon 402-752, Korea. kwak1014@inha.ac.kr

Abstract

Capsaicin, the pungent ingredient in hot pepper, activates nociceptors to produce pain and inflammation. However, prolonged exposures of capsaicin will cause desensitization to nociceptive stimuli. Hyperpolarization-activated cation currents (Ih) contribute to the maintenance of the resting membrane potential and excitability of neurons. In the cultured dorsal root ganglion (DRG) neurons, we investigated mechanisms underlying capsaicin-mediated modulation of Ih using patch clamp recordings. Capsaicin (1 microM) inhibited Ih only in the capsaicin-sensitive neurons. The capsaicin-induced inhibition of Ih was prevented by preexposing the TRPV1 antagonist, capsazepine (CPZ). Capsaicin-induced inhibition of Ih was dose dependent (IC50= 0.68 microM) and partially abolished by intracellular BAPTA and cyclosporin A, specific calcineurin inhibitor. In summary, the inhibitory effects of capsaicin on Ih are mediated by activation of TRPV1 and Ca(2+)-triggered cellular responses. Analgesic effects of capsaicin have been thought to be related to desensitization of nociceptive neurons due to depletion of pain-related substances. In addition, capsaicin-induced inhibition of Ih is likely to be important in understanding the analgesic mechanism of capsaicin.

Keyword

capsaicin; DRG neuron; hyperpolarization-activated cation current; rat
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