capsazepine and carvone

Transient receptor potential (TRP) channels in the spinal dorsal horn lamina II (substantia gelatinosa; SG), which are involved in the modulation of nociceptive transmission, have not yet been fully examined in property. Activation of the TRP channels by various plant-derived chemicals results in an increase in the spontaneous release of L-glutamate onto the SG neurons. We examined the effects of a monoterpene ketone (-)-carvone (contained in spearmint) and its stereoisomer (+)-carvone (in caraway) on glutamatergic spontaneous excitatory transmission in SG neurons of adult rat spinal cord slices by using the whole-cell patch-clamp technique. (-)-Carvone and (+)-carvone increased the frequency of spontaneous excitatory postsynaptic current (sEPSC) in a reversible and concentration-dependent manner with a small increase in its amplitude. Half-maximal effective concentrations of (-)-carvone and (+)-carvone in increasing sEPSC frequency were 0.70 mM and 0.72 mM, respectively. The (-)-carvone but not (+)-carvone activity was inhibited by a TRPV1 antagonist capsazepine. On the other hand, the (+)-carvone but not (-)-carvone activity was inhibited by a TRPA1 antagonist HC-030031. These results indicate that (-)-carvone and (+)-carvone activate TRPV1 and TRPA1 channels, respectively, resulting in an increase in spontaneous L-glutamate release onto SG neurons, with almost the same efficacy. Such a difference in TRP activation between the stereoisomers may serve to know the properties of TRP channels in the SG.

Topics: Acetanilides; Animals; Capsaicin; Cyclohexane Monoterpenes; Excitatory Postsynaptic Potentials; Glutamic Acid; Male; Monoterpenes; Neurons; Patch-Clamp Techniques; Purines; Rats; Rats, Sprague-Dawley; Stereoisomerism; Substantia Gelatinosa; Synaptic Transmission; Transient Receptor Potential Channels; TRPA1 Cation Channel; TRPC Cation Channels; TRPV Cation Channels

(-)-Carvone is an antinociceptive monoterpene found as the main active constituent of essential oils obtained from plants of the genus Mentha. Here, we have investigated the pharmacology of this monoterpene in dorsal root ganglia (DRG) neurons and TRPV1-expressing HEK293 cells. (-)-carvone at pharmacological active concentrations did not reveal significant cytotoxicity to the cells used in this study, as investigated by neutral red and propidium iodide flow cytometry assays. In calcium imaging experiments 1 mM (-)-carvone increased the cytosolic calcium levels in DRG neurons from 120.6 ± 5.0 nM (basal) to 310.7 ± 23.1 nM (P < 0.05). These effects were completely abolished when neurons were preincubated with calcium-free bath solution or ruthenium-red (5 µM) and capsazepine (10 µM), suggesting the possibility of TRPV1 channel-activation by (-)-carvone. Activity of (-)-carvone on TRPV1 channels was further investigated in HEK293 cells expressing recombinant human TRPV1 channels revealing dose-dependent calcium transients with an EC(50) of 1.3 ± 0.2 mM (Hill coefficient = 2.5). In conclusion, we show for the first time the ability of (-)-carvone to induce increases in cytosolic calcium concentration through TRPV1 activation.

Topics: Animals; Calcium Signaling; Capsaicin; Cell Survival; Cyclohexane Monoterpenes; HEK293 Cells; Humans; Monoterpenes; Neurons; Rats; Rats, Wistar; TRPV Cation Channels