Berntson Amy, Smith Robert G, Taylor W Rowland
John Curtin School of Medical Research and Centre for Visual Sciences, Australian National University, Canberra, Australia.
Vis Neurosci. 2004 Nov-Dec;21(6):913-24. doi: 10.1017/S095252380421611X.
Light-evoked currents were recorded from rod bipolar cells in a dark-adapted mouse retinal slice preparation. Low-intensity light steps evoked a sustained inward current. Saturating light steps evoked an inward current with an initial peak that inactivated, with a time constant of about 60-70 ms, to a steady plateau level that was maintained for the duration of the step. The inactivation was strongest at hyperpolarized potentials, and absent at positive potentials. Inactivation was mediated by an increase in the intracellular calcium concentration, as it was abolished in cells dialyzed with 10 mM BAPTA, but was present in cells dialyzed with 1 mM EGTA. Moreover, responses to brief flashes of light were broader in the presence of intracellular BAPTA indicating that the calcium feedback actively shapes the time course of the light responses. Recovery from inactivation observed for paired-pulse stimuli occurred with a time constant of about 375 ms. Calcium feedback could act to increase the dynamic range of the bipolar cells, and to reduce variability in the amplitude and duration of the single-photon signal. This may be important for nonlinear processing at downstream sites of convergence from rod bipolar cells to AII amacrine cells. A model in which intracellular calcium rapidly binds to the light-gated channel and reduces the conductance can account for the results.
在暗适应的小鼠视网膜切片标本中记录视杆双极细胞的光诱发电流。低强度光阶跃诱发持续内向电流。饱和光阶跃诱发一个具有初始峰值的内向电流，该峰值在约60 - 70毫秒的时间常数内失活，至稳定的平台水平，并在光阶跃持续期间保持。失活在超极化电位时最强，在正电位时不存在。失活由细胞内钙浓度增加介导，因为在用10 mM BAPTA透析的细胞中失活被消除，但在用1 mM EGTA透析的细胞中存在。此外，在细胞内存在BAPTA的情况下，对短暂闪光的反应更宽，表明钙反馈积极塑造光反应的时间进程。对于双脉冲刺激观察到的失活恢复发生的时间常数约为375毫秒。钙反馈可能起到增加双极细胞动态范围的作用，并减少单光子信号幅度和持续时间的变异性。这对于从视杆双极细胞到AII无长突细胞的下游汇聚部位的非线性处理可能很重要。一个细胞内钙快速结合到光门控通道并降低电导的模型可以解释这些结果。
