MODULATION OF TRANSMISSION GAIN BY PROTONS AT THE PHOTORECEPTOR OUTPUT SYNAPSE
MODULATION OF TRANSMISSION GAIN BY PROTONS AT THE PHOTORECEPTOR OUTPUT SYNAPSE
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DOI：
10.1073/pnas.90.21.10081
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发表时间：
1993-11-01
影响因子：
11.1
通讯作者：
MAHMUD, F
中科院分区：
文献类型：
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作者：
BARNES, S;MERCHANT, V;MAHMUD, F
用全细胞膜片钳技术研究了虎蝾螈（Ambystoma tigrinum）视网膜薄片光感受器对光反应的突触传递。突触强度是由细胞外的pH值调制在一个惊人的方式：光敏突触后电流在水平和双极细胞被发现是pH值的指数函数，表现出一个e倍增加每0.23 pH单位的pH范围从7到8。在分离的光感受器的钙通道电流进行了测量，也表现出质子敏感性。外部碱化从pH 7至8的通道激活的电压依赖性转移负12 mV。突触传递函数模型表明，突触前钙通道可能是质子作用的主要部位。碱化引起的钙内流和递质释放增加，可引起更大的突触后电流。这些结果表明，已知发生在视网膜中的活性依赖性间质pH值变化，而不减轻在该突触处的信号剪切，可能提供控制在光感受器输出突触处的增益的适应性机制。
Synaptic transmission of the light response from photoreceptors to second-order cells of the retina was studied with the whole-cell patch-clamp technique in tiger salamander (Ambystoma tigrinum) retinal slices. Synaptic strength is modulated by extracellular pH in a striking manner: Light-sensitive postsynaptic currents in horizontal and bipolar cells were found to be exponential functions of pH, exhibiting an e-fold increase per 0.23 pH unit over the pH range from 7 to 8. Calcium channel currents in isolated photoreceptors were measured and also exhibited proton sensitivity. External alkalinization from pH 7 to 8 shifted the voltage dependence of channel activation negative by 12 mV. A model of the synaptic transfer function suggested that presynaptic Ca channels could be the primary sites of proton action. Increased Ca influx and transmitter release brought about by alkalinization give rise to larger postsynaptic currents. These results suggest that activity-dependent interstitial pH changes known to occur in the retina, while not alleviating signal clipping at this synapse, may provide an adaptative mechanism controlling gain at the photoreceptor output synapse.