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Neuroscience. 1993 Aug;55(4):1015-23.

The role of calcium in capsaicin-induced desensitization in rat cultured dorsal root ganglion neurons.

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1
Sandoz Institute for Medical Research, London, U.K.

Abstract

The effects of capsaicin cytosolic Ca2+ concentration ([Ca2+]i) were measured in individual dorsal root ganglion neurons of the rat in culture. Capsaicin produced a rapid concentration-dependent (EC50 value of 72 nM) increase in [Ca2+]i which was entirely dependent on Ca2+ entry. Exposure of the neurons to a high concentration of capsaicin resulted in desensitization, but only in the presence of external Ca2+. Raising [Ca2+]i with a depolarizing concentration of potassium or the Ca2+ ionophore ionomycin did not reduce the response to a subsequent application of capsaicin. Capsaicin did not induce desensitization in Ca(2+)-free medium even if [Ca2+]i was simultaneously raised with a combination of ionomycin plus carbonyl cyanide m-chlorophenyl-hydrazone. Okadaic acid, a known inhibitor of protein phosphatases 1 and 2A, caused a transient dose-dependent (EC50 value, 100nM) rise in [Ca2+]i, but had no effect on either the responsiveness to capsaicin or capsaicin induced desensitization. The capsaicin antagonist capsazepine blocked the increase in [Ca2+]i evoked by capsaicin and prevented desensitization. These results suggest that desensitization requires the presence of extracellular Ca2+, cannot be mimicked by raising the concentration of [Ca2+]i and may involve Ca2+ entry through activated capsaicin-operated ion channels.

PMID:
7694175
DOI:
10.1016/0306-4522(93)90315-7
[Indexed for MEDLINE]

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