Huang S J, Robinson D W
Department of Biochemistry, University of California, Davis 95616, USA.
Neuroscience. 1998 Jul;85(1):239-47. doi: 10.1016/s0306-4522(97)00351-5.
The correlated activity of developing retinal ganglion cells is essential for the reorganization and refinement of retinogeniculate projections. Previous studies have uncovered marked changes in the spiking properties of retinal ganglion cells during this period of reorganization; however, a full understanding of the changes in the underlying ionic conductances has yet to be obtained. To this end, the whole-cell configuration of the patch-clamp technique was used to record currents conducted by voltage-gated calcium channels in 83 dissociated cat retinal ganglion cells obtained from animals aged between embryonic day 34 and postnatal day 105. Calcium currents, magnified by using barium as the major charge carrier, were isolated by substituting choline for Na+ in the bathing solution and Cs+ for K+ in the electrode solution. Three voltage-gated Ca2+ conductances were identified based on their voltage dependence and kinetics of activation and inactivation: a transient low-voltage-activated conductance, a transient high-voltage-activated conductance and a sustained high-voltage-activated conductance. During the developmental period examined there were significant increases in the densities of all three conductances, as well as significant changes in some of their activation and inactivation properties. These findings, together with those reported previously for the voltage-gated Na+ and K+ conductances, are related to the generation of excitability in developing retinal ganglion cells during a period critical to the normal development of the visual system. Furthermore, while the sustained high-voltage-activated conductance was present in all of the retinal ganglion cells observed, only about 72% expressed the transient high-voltage-activated current. During the developmental period examined, there was also an increase in the proportion of cells expressing the transient low-voltage-activated conductance. This, along with our previous finding that retinal ganglion cells heterogeneously express different types of voltage-gated K+ channels, strongly suggests that the spiking patterns observed in different classes of retinal ganglion cell may be due, in part, to their intrinsic membrane properties.
发育中的视网膜神经节细胞的相关活动对于视网膜膝状体投射的重组和精细化至关重要。先前的研究已经揭示了在此重组期间视网膜神经节细胞的放电特性发生了显著变化；然而，对于潜在离子电导变化的全面理解尚未实现。为此，采用膜片钳技术的全细胞配置来记录从胚胎第34天到出生后第105天的动物中分离出的83个猫视网膜神经节细胞中电压门控钙通道传导的电流。通过在浴液中用胆碱替代Na+以及在电极溶液中用Cs+替代K+，以钡作为主要电荷载体放大的钙电流被分离出来。基于其电压依赖性以及激活和失活动力学，确定了三种电压门控Ca2+电导：一种瞬时低电压激活电导、一种瞬时高电压激活电导和一种持续高电压激活电导。在所研究的发育期间，所有这三种电导的密度都有显著增加，并且它们的一些激活和失活特性也有显著变化。这些发现，连同先前报道的关于电压门控Na+和K+电导的发现，与在视觉系统正常发育的关键时期发育中的视网膜神经节细胞兴奋性的产生有关。此外，虽然在所观察的所有视网膜神经节细胞中都存在持续高电压激活电导，但只有约72%的细胞表达瞬时高电压激活电流。在所研究的发育期间，表达瞬时低电压激活电导的细胞比例也有所增加。这与我们先前的发现——视网膜神经节细胞异质性地表达不同类型的电压门控K+通道——一起，强烈表明在不同类别的视网膜神经节细胞中观察到的放电模式可能部分归因于它们内在的膜特性。
