Effects of capsaicin on Ca(2+) release from the intracellular Ca(2+) stores in the dorsal root ganglion cells of adult rats.

We have investigated the effect of capsaicin on Ca(2+) release from the intracellular calcium stores. Intracellular calcium concentration (Ca(2+)) was measured in rat dorsal root ganglion (DRG) neurons using microfluorimetry with fura-2 indicator. Brief application of capsaicin (1 microM) elevated Ca(2+) in Ca(2+)-free solution. Capsaicin-induced Ca(2+) transient in Ca(2+)-free solution was evoked in a dose-dependent manner. Resiniferatoxin, an analogue of capsaicin, also raised Ca(2+) in Ca(2+)-free solution. Capsazepine, an antagonist of capsaicin receptor, completely blocked the capsaicin-induced Ca(2+) transient. Caffeine completely abolished capsaicin-induced Ca(2+) transient. Dantrolene sodium and ruthenium red, antagonists of the ryanodine receptor, blocked the effect of capsaicin on Ca(2+). However, capsaicin-induced Ca(2+) transient was not affected by 2-APB, a membrane-permeable IP(3) receptor antagonist. Furthermore, depletion of IP(3)-sensitive Ca(2+) stores by bradykinin and phospholipase C inhibitors, neomycin, and U-73122, did not block capsaicin-induced Ca(2+) transient. In conclusion, capsaicin increases Ca(2+) through Ca(2+) release from ryanodine-sensitive Ca(2+) stores, but not from IP(3)-sensitive Ca(2+) stores in addition to Ca(2+) entry through capsaicin-activated nonselective cation channel in rat DRG neurons.