Pan Z H
Department of Anatomy, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
J Neurophysiol. 2000 Jan;83(1):513-27. doi: 10.1152/jn.2000.83.1.513.
Whole cell voltage-clamp recordings were performed to investigate voltage-activated Ca(2+) currents in acutely isolated retinal bipolar cells of rats. Two groups of morphologically different bipolar cells were observed. Bipolar cells of the first group, which represent the majority of isolated bipolar cells, were immunoreactive to protein kinase C (PKC) and, therefore likely to be rod bipolar cells. Bipolar cells of the second group, which represent only a small population of isolated bipolar cells, did not show PKC immunoreactivity and were likely to be cone bipolar cells. The validity of morphological identification of bipolar cells was further confirmed by the presence of GABA(C) responses in these cells. Bipolar cells of both groups displayed low-voltage-activated (LVA) Ca(2+) currents with similar voltage dependence of activation and steady-state inactivation. However, the activation, inactivation, and deactivation kinetics of the LVA Ca(2+) currents between rod and cone bipolar cells differed. Particularly, the LVA Ca(2+) currents of rod bipolar cells displayed both transient and sustained components. In contrast, the LVA Ca(2+) currents of cone bipolar cells were mainly transient. In addition, the LVA Ca(2+) channels of rod bipolar cells were more permeable to Ba(2+) than to Ca(2+), whereas those of cone bipolar cells were equally or less permeable to Ba(2+) than to Ca(2+). The LVA Ca(2+) currents of both rod and cone bipolar cells were antagonized by high concentrations of nimodipine with IC(50) of 17 and 23 microM, respectively, but largely resistant to Cd(2+) and Ni(2+). Bipolar cells of both groups also displayed high-voltage-activated (HVA) Ca(2+) currents. The HVA Ca(2+) currents were, at least in part, to be L-type that were potentiated by BayK-8644 (1 microM) and largely antagonized by low concentrations of nimodipine (5 microM). The L-type Ca(2+) channels were almost exclusively located at the axon terminals of rod bipolar cells but expressed at least in the cell soma of cone bipolar cells. Results of this study indicate that rod and cone bipolar cells of the mammalian retina differentially express at least two types of LVA Ca(2+) channels. Rod and cone bipolar cells also show different spatial distribution of L-type Ca(2+) channels.
采用全细胞电压钳记录技术，研究大鼠急性分离视网膜双极细胞中的电压门控性Ca(2+)电流。观察到两组形态不同的双极细胞。第一组双极细胞占分离出的双极细胞的大多数，对蛋白激酶C（PKC）呈免疫反应性，因此可能是视杆双极细胞。第二组双极细胞仅占分离出的双极细胞的一小部分，不显示PKC免疫反应性，可能是视锥双极细胞。这些细胞中GABA(C)反应的存在进一步证实了双极细胞形态学鉴定的有效性。两组双极细胞均表现出低电压激活（LVA）Ca(2+)电流，其激活和稳态失活的电压依赖性相似。然而，视杆和视锥双极细胞之间LVA Ca(2+)电流的激活、失活和去激活动力学有所不同。特别是，视杆双极细胞的LVA Ca(2+)电流表现出瞬时和持续两种成分。相比之下，视锥双极细胞的LVA Ca(2+)电流主要是瞬时的。此外，视杆双极细胞的LVA Ca(2+)通道对Ba(2+)的通透性比对Ca(2+)的通透性更高，而视锥双极细胞的LVA Ca(2+)通道对Ba(2+)的通透性与对Ca(2+)的通透性相当或更低。视杆和视锥双极细胞的LVA Ca(2+)电流均被高浓度尼莫地平拮抗，其IC(50)分别为17和23 microM，但对Cd(2+)和Ni(2+)具有很大抗性。两组双极细胞也表现出高电压激活（HVA）Ca(2+)电流。HVA Ca(2+)电流至少部分是L型的，可被BayK-8644（1 microM）增强，并被低浓度尼莫地平（5 microM）很大程度地拮抗。L型Ca(2+)通道几乎只位于视杆双极细胞的轴突末端，但至少在视锥双极细胞的胞体中表达。本研究结果表明，哺乳动物视网膜的视杆和视锥双极细胞至少差异表达两种类型的LVA Ca(2+)通道。视杆和视锥双极细胞在L型Ca(2+)通道的空间分布上也有所不同。
