Modulation of sensory neuron potassium conductances by anandamide indicates roles for metabolites.
OBJECTIVE
The endogenous cannabinoid anandamide (AEA) acts at cannabinoid (CB(1)) and vanilloid (TRPV(1)) receptors. AEA also shows antinociceptive properties; although the underlying mechanism for this is not fully understood, both CB(1) and TRPV(1) may be involved. Voltage-activated Ca(2+) channels in rat-cultured dorsal root ganglion (DRG) neurons are modulated by AEA. However, AEA in different populations of neurons enhanced or attenuated KCl-evoked Ca(2+) influx; these effects were linked with soma size. The aim of this study was to determine how AEA or its metabolites might produce these variable responses.


METHODS
The whole cell patch-clamp technique and fura-2 Ca(2+) imaging were used to characterize the actions of AEA on action potential firing and voltage-activated K(+) currents and to determine whether AEA metabolism plays any role in its effects on cultured DRG neurons.


RESULTS
AEA attenuated multiple action potential firing evoked by 300 ms depolarizing current commands in a subpopulation of DRG neurons. Application of 1 microM AEA attenuated voltage-activated K(+) currents and the recovery of KCl-evoked Ca(2+) transients. The insensitivity of these responses to the CB(1) receptor antagonist rimonabant (100 nM) and preincubation of DRG neurons with pertussis toxin suggested that these actions are not CB(1) receptor-mediated. Preincubating DRG neurons with the fatty acid amide hydrolase (FAAH) inhibitor phenylmethylsulphonyl fluoride (PMSF) attenuated the inhibitory actions of AEA on K(+) currents and Ca(2+) influx.


CONCLUSIONS
These data suggest that the products of AEA metabolism by FAAH contribute to the attenuation of K(+) conductances and altered excitability of cultured sensory neurons.
Evans
R M
RM
School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, UK.
Wease
K N
KN
MacDonald
C J
CJ
Khairy
H A
HA
Ross
R A
RA
Scott
R H
RH
D000200:Action Potentials; D000581:Amidohydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D001095:Arachidonic Acids / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D002478:Cells, Cultured; D004558:Electric Stimulation; D063388:Endocannabinoids; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D009475:Neurons, Afferent / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010664:Phenylmethylsulfonyl Fluoride / Q000494:pharmacology; D053284:Polyunsaturated Alkamides / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D043882:Receptors, Cannabinoid / Q000378:metabolism; D000099252:Fatty Acid Amide Hydrolases
D000581:Amidohydrolases; D001095:Arachidonic Acids; D002118:Calcium; D015220:Calcium Channels; D063388:Endocannabinoids; D004791:Enzyme Inhibitors; D010664:Phenylmethylsulfonyl Fluoride; D053284:Polyunsaturated Alkamides; D011188:Potassium; D024642:Potassium Channels, Voltage-Gated; D011189:Potassium Chloride; D043882:Receptors, Cannabinoid; D000099252:Fatty Acid Amide Hydrolases; C078814:anandamide