Korean J Physiol Pharmacol Vol 16: 139－144, April, 2012 http://dx.doi.org/10.4196/kjpp.2012.16.2.139 TRPC-Mediated Current Is Not Involved in Endocannabinoid-Induced Short-Term Depression in Cerebellum W onseok Chang1, Joo Min Park1, Jun Kim1, and Sang Jeong Kim1,2 Departments of 1Physiology, 2Brain and Cognitive Sciences, Seoul National University College of Medicine, Seoul 110-799, Korea It has been reported that activation of metabotropic glutamate receptor 1 (mGluR1) can mediate endocannabinoid-induced short-term depression of synaptic transmission in cerebellar parallel fiber (PF)-Purkinje cell (PC) synapse. mGluR1 has signaling pathways involved in intracellular calcium increase which may contribute to endocannabinoid release. Two major mGluR1-evoked calcium signaling pathways are known: (1) slow-kinetic inward current carried by transient receptor potential canonical (TRPC) channel which is permeable to Ca2＋; (2) IP3-induced calcium release from intra- cellular calcium store. However, it is unclear how much each calcium source contributes to endocannabinoid signaling. Here, we investigated whether calcium influx through mGluR1-evoked TRPC channel contributes to endocannabinoid signaling in cerebellar Purkinje cells. At first, we applied SKF96365 to inhibit TRPC, which blocked endocannabinoid-induced short-term depression completely. However, an alternative TRP channel inhibitor, BTP2 did not affect endocannabinoid-induced short-term depression although it blocked mGluR1-evoked TRPC currents. Endocannabinoid signaling occurred normally even though the TRPC current was mostly blocked by BTP2. Our data imply that TRPC current does not play an important role in endocannabinoid signaling. W e also suggest precaution in applying SKF96365 to inhibit TRP channels and propose BTP2 as an alternative TRPC inhibitor. Key Words: Endocannabinoid, TRPC, Short-term depression, Cerebellar Purkinje cell, BTP2 INTRODUCTION Metabotropic glutamate receptors (mGluRs) are a type of G-protein coupled receptor that modulate protein ex- pression, neurotransmission and neuronal excitability throughout the CNS [1-4]. mGluR1 is a member of a Group I mGluR that is expressed in cerebellar Purkinje cells and in many other postsynaptic neurons. Activation of mGluR1 induces several cellular events in cerebellar Purkinje cells like the activation of PLC-β-IP3 signal cascade [5,6] or slow excitatory postsynaptic currents (EPSCs) [7,8]. Slow cur- rents are known to be mediated by transient receptor po- tential canonical (TRPC) channels [8]. Slow currents are non-selective cation currents which include Na＋ and Ca2＋ influxes [9] so it may elevate intracellular Ca2＋ concen- tration in cerebellar Purkinje cells. The function of such slow currents is still unknown, however. Received February 28, 2012, Revised March 25, 2012, Accepted March 25, 2012 Corresponding to: Sang Jeong Kim, Department of Physiology, Seoul National University College of Medicine, 28, Yeongon-dong, Chongro-gu, Seoul 110-744, Korea. (Tel) 82-2-740-8229, (Fax) 82-2- 763-9667, (E-mail) sangjkim@snu.ac.kr This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 139 Delta-9-tetrahydrocannabinol (Δ9-THC), the principal psychoactive constituent of marijuana affects brain func- tion by activating the G-protein coupled receptor, cannabi- noid receptor-1 (CB1R) [10,11], which is expressed through- out the brain [12]. Two major endogenous ligands of the receptor, 2-arachidonylglycereol (2-AG) and anandamide are known so far [13,14]. Endocannabinoids function as a retrograde messenger that contributes to long-term and short-term plasticity in the CNS [15-17]. It is reported that strong depolarization of postsynaptic neurons [18,19] or ad- ministration of mGluR agonists [20,21] can suppress pre- synaptic transmitter release and diminish EPSCs. It is found that the depression of EPSCs has an endocannabi- noid-dependent mechanism and three different models for the mechanism of endocannabinoid release have been suggested. Endocannabinoids are released by large ele- vation of calcium concentration in the postsynaptic neuron that is usually induced by strong depolarization (depolari- zation-induced suppression of inhibition/excitation, DSI/ DSE), strong activation of G protein-coupled receptors (receptor-driven endocannabinoid release, RER), or simul- taneous small elevations of calcium concentration and weak ABBREVIATIONS: PF, parallel fiber; PC, Purkinje cell; EPSC, excitatory postsynaptic current; TRPC channel, transient receptor potential canonical channel; CB1R, cannabinoid receptor-1; mGluR, metabotropic glutamate receptor; DSI/DSE, depolarization-induced suppression of inhibition/excitation; RER, receptor-driven endocanna- binoid release; Ca-RER, Ca2＋-assisted RER; VOCC: voltage-operated calcium channel; ER, endoplasmic reticulum; CF, climbing fiber.