Capsaicin-induced desensitization is prevented by capsazepine but not by ruthenium red in guinea pig bronchi.

In isolated guinea pig bronchi, the influence of ruthenium red, capsazepine and extracellular Ca2+ on capsaicin-induced desensitization was examined to investigate whether this desensitization was mediated via a specific receptor coupled with an ion channel. Pre-exposure of tissues to capsaicin (1, 3 or 10 microM) caused a dose-dependent desensitization to the second application of capsaicin. However, the contractile responses to exogenous tachykinins were not changed after pre-exposure of tissues to capsaicin. This capsaicin-induced desensitization was prevented by capsazepine (30 microM), but not by ruthenium red added to tissues 20 min before pretreatment with capsaicin (3 microM). While the excitatory contractile response to capsaicin was markedly reduced in the absence of extracellular Ca2+, the desensitization induced by capsaicin was not changed by the removal of extracellular Ca2+. In summary, the results from the present study suggest that in vitro functional desensitization induced by capsaicin in guinea pig bronchi may involve changes in the vanilloid receptor and occur through a ruthenium red-insensitive pathway.