Wang Y, Rowan M J, Anwyl R
Department of Physiology, Trinity College, Dublin, Ireland.
J Neurophysiol. 1997 Feb;77(2):812-25. doi: 10.1152/jn.1997.77.2.812.
The mechanisms of the induction of long-term depression (LTD) of field excitatory postsynaptic potentials (EPSPs) and whole cell patch-clamped excitatory postsynaptic currents (EPSCs) were studied in the dentate gyrus of the rat hippocampus. LTD of field EPSPs measuring 40% of control at 30 min poststimulation was induced by low-frequency stimulation consisting of 900 pulses at 1 Hz. LTD of EPSCs measuring 37% of control was induced by a pairing procedure consisting of 60 pulses at 1 Hz applied under voltage clamp at a holding potential of -40 mV. The induction of LTD of field EPSPs was dependent on an influx of extracellular calcium, being reduced in a low-Ca2+ (0.8 mM) medium. However, substantial LTD (26%) was still induced in such a medium, demonstrating the relatively low sensitivity of LTD induction to the level of extracellular Ca2+. A high concentration of the N-methyl-D-aspartate receptor antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-AP5) (100 microM) did not significantly inhibit the induction of LTD of EPSCs evoked by the intracellular pairing procedure. D-AP5 partially reduced the magnitude of LTD of field EPSPs, but substantial LTD was still induced in the presence of AP5. The induction of LTD was strongly inhibited by Ni2+ (50 microM) but not by nifedipine (10 microM), indicating that Ca2+ influx via T-type, but not L-type, Ca2+ channels is required for the induction of LTD. The induction of LTD was strongly inhibited by thapsigargin, an agent known to deplete intracellular Ca2+ stores. The induction of LTD, but not long-term potentiation (LTP), was also strongly inhibited by ruthenium red, an agent known to block the ryanodine receptors located on intracellular Ca2+ stores. These results demonstrate that Ca2+ release from intracellular Ca2+ stores is required for the induction of LTD, but not LTP. The results of the present experiments suggest that the induction of LTD involves the entry of Ca2+ via low-voltage-activated voltage-gated Ca2+ channels followed by release of Ca2+ from intracellular ryanodine-receptor-sensitive Ca2+ stores.
我们研究了大鼠海马齿状回中诱发场兴奋性突触后电位（EPSP）和全细胞膜片钳记录的兴奋性突触后电流（EPSC）长时程抑制（LTD）的机制。通过1 Hz的900个脉冲组成的低频刺激，在刺激后30分钟诱发了场EPSP的LTD，其幅度为对照的40%。通过在-40 mV的钳制电位下电压钳施加1 Hz的60个脉冲组成的配对程序，诱发了EPSC的LTD，其幅度为对照的37%。场EPSP的LTD诱导依赖于细胞外钙的内流，在低钙（0.8 mM）培养基中其幅度降低。然而，在这种培养基中仍能诱发相当程度的LTD（26%），这表明LTD诱导对细胞外钙水平的敏感性相对较低。高浓度的N-甲基-D-天冬氨酸受体拮抗剂D-（-）-2-氨基-5-磷酸戊酸（D-AP5）（100 μM）并不能显著抑制细胞内配对程序诱发的EPSC的LTD诱导。D-AP5部分降低了场EPSP的LTD幅度，但在有AP5存在的情况下仍能诱发相当程度的LTD。LTD的诱导受到Ni2+（50 μM）的强烈抑制，但不受硝苯地平（10 μM）的抑制，这表明LTD的诱导需要通过T型钙通道而非L型钙通道的钙内流。LTD的诱导受到毒胡萝卜素的强烈抑制，毒胡萝卜素是一种已知能耗尽细胞内钙储存的药物。LTD的诱导也受到钌红的强烈抑制，钌红是一种已知能阻断位于细胞内钙储存上的ryanodine受体的药物，但长时程增强（LTP）不受影响。这些结果表明，细胞内钙储存的钙释放是LTD诱导所必需的，但不是LTP诱导所必需的。本实验结果表明，LTD的诱导涉及通过低电压激活的电压门控钙通道的钙内流，随后从细胞内ryanodine受体敏感的钙储存中释放钙。
