title: Preferential block of inactivation-deficient Na+ currents by capsaicin reveals a non-TRPV1 receptor within the Na+ channel.
abstract: Capsaicin elicits burning pain via the activation of the vanilloid receptor (TRPV1). Intriguingly, several reports showed that capsaicin also inhibits Na+ currents but the mechanisms remain unclear. To explore this non-TRPV1 action we applied capsaicin to HEK293 cells stably expressing inactivation-deficient rat skeletal muscle Na+ mutant channels (rNav1.4-WCW). Capsaicin elicited a conspicuous time-dependent block of inactivation-deficient Na+ currents. The 50% inhibitory concentration (IC50) of capsaicin for open Na+ channels at +30 mV was measured 6.8+/-0.6 microM (n=5), a value that is 10-30 times lower than those for resting (218 microM) and inactivated (74 microM) wild-type Na+ channels. On-rate and off-rate constants for capsaicin open-channel block at +30 mV were estimated to be 6.37 microM(-1) s(-1) and 34.4 s(-1), respectively, with a calculated dissociation constant (KD) of 5.4 microM. Capsaicin at 30 microM produced approximately 70% additional use-dependent block of remaining rNav1.4-WCW Na+ currents during repetitive pulses at 1 Hz. Site-directed mutagenesis showed that the local anesthetic receptor was not responsible for the capsaicin block of the inactivation-deficient Na+ channel. Interestingly, capsaicin elicited little time-dependent block of batrachotoxin-modified rNav1.4-WCW Na+ currents, indicating that batrachotoxin prevents capsaicin binding. Finally, neuronal open Na+ channels endogenously expressed in GH3 cells were as sensitive to capsaicin block as rNav1.4 counterparts. We conclude that capsaicin preferentially blocks persistent late Na+ currents, probably via a receptor that overlaps the batrachotoxin receptor but not the local anesthetic receptor. Drugs that target such a non-TRPV1 receptor could be beneficial for patients with neuropathic pain.
authors.affiliation: Department of Biology, State University of New York at Albany, Albany, NY, United States.
authors.forename: Sho-Ya
authors.initials: SY
authors.lastname: Wang
authors.forename: Jane
authors.initials: J
authors.lastname: Mitchell
authors.forename: Ging Kuo
authors.initials: GK
authors.lastname: Wang
mesh_terms: D000818:Animals; D002211:Capsaicin / Q000008:administration & dosage*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007668:Kidney / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D026941:Sodium Channel Blockers / Q000008:administration & dosage; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D050916:TRPV Cation Channels / Q000737:chemistry / Q000378:metabolism*
chemical_list: D026941:Sodium Channel Blockers; D015222:Sodium Channels; D050916:TRPV Cation Channels; C494484:TRPV1 receptor; D002211:Capsaicin