Verweij J, Kamermans M, Spekreijse H
Graduate School Neurosciences, Amsterdam, The Netherlands.
Vision Res. 1996 Dec;36(24):3943-53. doi: 10.1016/s0042-6989(96)00142-3.
We studied feedback from horizontal cells to cones in isolated goldfish retinae and found that surround stimuli evoke an inward current and a slowly developing outward current. The surround-evoked currents are blocked by the glutamate antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) and are, like horizontal cell responses, most effectively evoked by large stimuli. This indicates that the currents are caused by feedback from horizontal cells. The surround-evoked inward current is neither blocked by picrotoxin nor carried by chloride. Instead, it is carried by calcium, and it triggers a slowly developing calcium-dependent chloride current. We were unable to mimick the surround-evoked currents by modulating the extracellular GABA concentration. We conclude that when horizontal cells hyperpolarize they feed back to the cones by shifting the cone calcium-current activation range to more negative potentials. This type of feedback, directly targeted at the calcium current, scarcely influences the membrane potential of the receiving neuron, but effectively modulates its synaptic output.
我们研究了分离的金鱼视网膜中水平细胞对视锥细胞的反馈，发现周边刺激会引发内向电流和缓慢发展的外向电流。周边刺激诱发的电流被谷氨酸拮抗剂6,7-二硝基喹喔啉-2,3-二酮（DNQX）阻断，并且与水平细胞反应一样，大刺激能最有效地诱发这些电流。这表明这些电流是由水平细胞的反馈引起的。周边刺激诱发的内向电流既不被印防己毒素阻断，也不是由氯离子携带。相反，它由钙离子携带，并触发缓慢发展的钙依赖性氯电流。我们无法通过调节细胞外GABA浓度来模拟周边刺激诱发的电流。我们得出结论，当水平细胞超极化时，它们会通过将视锥细胞钙电流的激活范围转移到更负的电位来反馈给视锥细胞。这种直接针对钙电流的反馈几乎不影响接收神经元的膜电位，但能有效地调节其突触输出。
