Pharmacological evidence for the involvement of diacylglycerol lipase in depolarization-induced endocanabinoid release.
Depolarization-induced suppression of inhibition (DSI) or excitation (DSE) is a well-known form of endocannabinoid-mediated short-term plasticity that is induced by postsynaptic depolarization. It is generally accepted that DSI/DSE is triggered by Ca(2+) influx through voltage-gated Ca(2+) channels. It is also demonstrated that DSI/DSE is mediated by 2-arachidonoylglycerol (2-AG). However, how Ca(2+) induces 2-AG production is still unclear. In the present study, we investigated molecular mechanisms underlying the Ca(2+)-driven 2-AG production. Using cannabinoid-sensitive inhibitory synapses of cultured hippocampal neurons, we tested several inhibitors for enzymes that are supposed to be involved in 2-AG metabolism. The chemicals we tested include inhibitors for phospholipase C (U73122 and ET-18), diacylglycerol kinase (DGK inhibitor 1), phosphatidic acid phosphohydrolase (propranolol), and diacylglycerol lipase (DGL; RHC-80267 and tetrahydrolipstatin (THL)). However, unfavorable side effects were observed with these inhibitors, except for THL. Furthermore, we found that RHC-80267 hardly inhibited the endocannabinoid release driven by G(q/11)-coupled receptors, which is thought to be DGL-dependent. By contrast, THL exhibited no side effects as long as we tested, and was confirmed to inhibit the DGL-dependent process. Using THL as a DGL inhibitor, we demonstrated that DGL is involved in both hippocampal DSI and cerebellar DSE. To test a possible involvement of PLCdelta in DSI, we examined hippocampal DSI in PLCdelta1, delta3 and delta4-knockout mice. However, there was no significant difference in the DSI magnitude between these knockout mice and wild-type mice. The present study clearly shows that DGL is a prerequisite for DSI/DSE. The enzymes yielding DG remain to be determined.
Hashimotodani
Yuki
Y
Department of Neurophysiology, Graduate School of Medicine, Osaka University, Suita 565-0871, Japan.
Ohno-Shosaku
Takako
T
Maejima
Takashi
T
Fukami
Kiyoko
K
Kano
Masanobu
M
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001095:Arachidonic Acids / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D063385:Cannabinoid Receptor Modulators / Q000378:metabolism*; D002478:Cells, Cultured; D004558:Electric Stimulation; D063388:Endocannabinoids; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005989:Glycerides / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D008071:Lipoprotein Lipase / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D018408:Patch-Clamp Techniques; D054803:Phospholipase C delta / Q000172:deficiency; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
D000319:Adrenergic beta-Antagonists; D001095:Arachidonic Acids; D063385:Cannabinoid Receptor Modulators; D063388:Endocannabinoids; D004791:Enzyme Inhibitors; D005989:Glycerides; C094503:glyceryl 2-arachidonate; D011433:Propranolol; D008071:Lipoprotein Lipase; D054803:Phospholipase C delta; D002118:Calcium