Hashimotodani Yuki, Ohno-Shosaku Takako, Tsubokawa Hiroshi, Ogata Hidenori, Emoto Ken, Maejima Takashi, Araishi Kenji, Shin Hee-Sup, Kano Masanobu
Department of Cellular Neurophysiology, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8640, Japan.
Neuron. 2005 Jan 20;45(2):257-68. doi: 10.1016/j.neuron.2005.01.004.
Endocannabinoids mediate retrograde signal and modulate transmission efficacy at various central synapses. Although endocannabinoid release is induced by either depolarization or activation of G(q/11)-coupled receptors, it is markedly enhanced by the coincidence of depolarization and receptor activation. Here we report that this coincidence is detected by phospholipase Cbeta1 (PLCbeta1) in hippocampal neurons. By measuring cannabinoid-sensitive synaptic currents, we found that the receptor-driven endocannabinoid release was dependent on physiological levels of intracellular Ca(2+) concentration (Ca(2+)), and markedly enhanced by depolarization-induced Ca(2+) elevation. Furthermore, we measured PLC activity in intact neurons by using exogenous TRPC6 channel as a biosensor for the PLC product diacylglycerol and found that the receptor-driven PLC activation exhibited similar Ca(2+) dependence to that of endocannabinoid release. Neither endocannabinoid release nor PLC activation was induced by receptor activation in PLCbeta1 knockout mice. We therefore conclude that PLCbeta1 serves as a coincidence detector through its Ca(2+) dependency for endocannabinoid release in hippocampal neurons.
内源性大麻素介导逆行信号，并调节各种中枢突触的传递效率。尽管内源性大麻素的释放可由去极化或G(q/11)偶联受体的激活所诱导，但去极化与受体激活同时发生时，其释放会显著增强。在此我们报告，海马神经元中的磷脂酶Cβ1（PLCβ1）可检测到这种同时发生的情况。通过测量对大麻素敏感的突触电流，我们发现受体驱动的内源性大麻素释放依赖于细胞内Ca(2+)浓度（[Ca(2+)]i）的生理水平，并因去极化诱导的[Ca(2+)]i升高而显著增强。此外，我们通过使用外源性TRPC6通道作为PLC产物二酰基甘油的生物传感器，测量了完整神经元中的PLC活性，发现受体驱动的PLC激活对[Ca(2+)]i的依赖性与内源性大麻素释放相似。在PLCβ1基因敲除小鼠中，受体激活既不诱导内源性大麻素释放，也不诱导PLC激活。因此，我们得出结论，PLCβ1通过其对海马神经元内源性大麻素释放的Ca(2+)依赖性，充当了一种同时发生情况的检测器。
