Beltrán-Matas Pablo, Hartveit Espen, Veruki Margaret L
Department of Biomedicine, University of Bergen, Bergen, Norway.
Front Ophthalmol (Lausanne). 2023 Apr 5;3:1134765. doi: 10.3389/fopht.2023.1134765. eCollection 2023.
Amacrine cells are a highly diverse group of inhibitory retinal interneurons that sculpt the responses of bipolar cells, ganglion cells, and other amacrine cells. They integrate excitatory inputs from bipolar cells and inhibitory inputs from other amacrine cells, but for most amacrine cells, little is known about the specificity and functional properties of their inhibitory inputs. Here, we have investigated GABA receptors of the AII amacrine, a critical neuron in the rod pathway microcircuit, using patch-clamp recording in rat retinal slices. Puffer application of GABA evoked robust responses, but, surprisingly, spontaneous GABA receptor-mediated postsynaptic currents were not observed, neither under control conditions nor following application of high-K solution to facilitate release. To investigate the biophysical and pharmacological properties of GABA receptors in AIIs, we therefore used nucleated patches and a fast application system. Both brief and long pulses of GABA (3 mM) evoked GABA receptor-mediated currents with slow, multi-exponential decay kinetics. The average weighted time constant (τ) of deactivation was ~163 ms. Desensitization was even slower, with τ ~330 ms. Non-stationary noise analysis of patch responses and directly observed channel gating yielded a single-channel conductance of ~23 pS. Pharmacological investigation suggested the presence of α2 and/or α3 subunits, as well as the γ2 subunit. Such subunit combinations are typical of GABA receptors with slow kinetics. If synaptic GABA receptors of AII amacrines have similar functional properties, the slow deactivation and desensitization kinetics will facilitate temporal summation of GABAergic inputs, allowing effective summation and synaptic integration to occur even for relatively low frequencies of inhibitory inputs.
无长突细胞是一类高度多样化的抑制性视网膜中间神经元，它们塑造双极细胞、神经节细胞和其他无长突细胞的反应。它们整合来自双极细胞的兴奋性输入和来自其他无长突细胞的抑制性输入，但对于大多数无长突细胞而言，关于其抑制性输入的特异性和功能特性知之甚少。在这里，我们使用大鼠视网膜切片的膜片钳记录法研究了视杆通路微电路中的关键神经元AII无长突细胞的GABA受体。通过压力施加GABA可诱发强烈反应，但令人惊讶的是，无论是在对照条件下还是在应用高钾溶液以促进释放后，均未观察到自发的GABA受体介导的突触后电流。因此，为了研究AII无长突细胞中GABA受体的生物物理和药理学特性，我们使用了有核膜片和快速施加系统。短暂和长时间的GABA（3 mM）脉冲均诱发了具有缓慢的多指数衰减动力学的GABA受体介导的电流。失活的平均加权时间常数（τ）约为163毫秒。脱敏甚至更慢，τ约为330毫秒。对膜片反应的非平稳噪声分析和直接观察到的通道门控产生了约23 pS的单通道电导。药理学研究表明存在α2和/或α3亚基以及γ2亚基。这种亚基组合是具有缓慢动力学的GABA受体的典型特征。如果AII无长突细胞的突触GABA受体具有相似的功能特性，那么缓慢的失活和脱敏动力学将促进GABA能输入的时间总和，即使对于相对较低频率的抑制性输入也能实现有效的总和和突触整合。
