Holmgaard Kim, Jensen Kimmo, Lambert John D C
Institute of Physiology and Biophysics, Building 1160, University of Aarhus, DK-8000 Aarhus C, Denmark.
Brain Res. 2009 Jan 16;1249:79-90. doi: 10.1016/j.brainres.2008.10.033. Epub 2008 Oct 28.
We have previously demonstrated that L-type Ca(2+) channels are involved in post-tetanic potentiation (PTP) of GABAergic IPSCs in cultured hippocampal neurons. Here we have used intracellular Fluo-3 to detect Ca(2+) in single GABAergic boutons in response to stimulation that evokes PTP. During control stimulation of the presynaptic GABAergic neuron at 40 Hz for 1-2 s, DeltaF/F(0) increased rapidly to a peak value and started to decline shortly after the train ended, returning to baseline within 10-20 s. The L-type channel blocker, isradipine (5 microM), had no significant effect on the amplitude or kinetics of the Ca(2+) signal. Following blockade of N- and P/Q-type Ca(2+)-channels, the amplitude was reduced by 52.9+/-3%. Isradipine caused a reduction of the remaining response (by 26.6+/-5%, P<0.01), that was fully reversible on washing. The L-type channel "agonist", BayK 8644 (8 microM), caused a significant enhancement of the peak (by 18.7%+/-7%, P<0.05). The rising phase of the Ca(2+) signal, which is related to the rate of entry of Ca(2+) into the bouton, was decreased by isradipine (by 25.5+/-6%, P<0.05) and enhanced by BayK 8644 (by 45.2%+/-16%, P<0.05). These Ca(2+) imaging experiments support the putative role of L-type channels in PTP of GABAergic synapses on cultured hippocampal neurons. We expect L-channels to be few in number, although they may couple strongly to intracellular signalling cascades that could amplify a signal that regulates synaptic vesicle turnover in the GABAergic boutons.
我们先前已经证明，L型Ca(2+)通道参与培养的海马神经元中GABA能抑制性突触后电流（IPSC）的强直后增强（PTP）。在此，我们使用细胞内Fluo-3来检测单个GABA能突触小体中响应诱发PTP的刺激时的[Ca(2+)]i。在以40 Hz对突触前GABA能神经元进行1-2 s的对照刺激期间，DeltaF/F(0)迅速增加至峰值，并在刺激串结束后不久开始下降，在10-20 s内恢复至基线。L型通道阻滞剂异搏定（5 microM）对Ca(2+)信号的幅度或动力学没有显著影响。在阻断N型和P/Q型Ca(2+)通道后，幅度降低了52.9+/-3%。异搏定使剩余反应降低（降低26.6+/-5%，P<0.01），洗脱后完全可逆。L型通道“激动剂”BayK 8644（8 microM）使峰值显著增强（增强18.7%+/-7%，P<0.05）。与Ca(2+)进入突触小体的速率相关的Ca(2+)信号上升期，异搏定使其降低（降低25.5+/-6%，P<0.05），BayK 8644使其增强（增强45.2%+/-16%，P<0.05）。这些Ca(2+)成像实验支持L型通道在培养的海马神经元中GABA能突触PTP中的假定作用。我们预计L通道数量较少，尽管它们可能与细胞内信号级联反应紧密耦合，这些信号级联反应可以放大调节GABA能突触小体中突触囊泡周转的信号。
