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A study on the mechanism of light adaptation of vertebrate photoreceptors with the patch clamp method.

膜片钳法研究脊椎动物感光细胞光适应机制。

基本信息

批准号：
63570068
负责人：
KONDO Hiroaki
金额：
$ 1.22万
依托单位：
St. Marianna University School of Medicine
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1989
项目状态：
已结题

项目摘要

There has been considerable speculation that decreased cytoplasmic Ca^<2+> concentration may play a role in light adaptation of vertebrate photoreceptors. In order to study the steady-state action of Ca^<2+> on the phototransduction cascade, we examined the effects of lowered external Ca^<2+> concentration, an phosphodiesterase inhibitor (IBMX), and several guanylate-cyclase excitants on flash responses of frog rods. Membrane current was recorded from an isolated, dark-adapted rod by sucking its inner segment into a glass pipette containing Ringer solution. The outer segment of the cell was exposed to bath solution which could be changed.During prolonged exposure ( >2min ) to 1-10muM Ca^<2+> solutions, the latency of flash responses was markedly increased and the recovery process was accelerated. The sensitivity to relatively dim flashes was reduced, but the saturating intensity of flash stimulation seemed to be same as that in the normal Ringer solution.Prolonged exposure ( >2min ) to 5-50)muM IBMX solutions increased the latency of flash responses and slowed both of the rising and recovery phases.Na-nitroprusside and unsaturated fatty acids (arachidonic acid and linoleic acid) which were intracellularly applied with patch electrodes produced only acceleration of the recovery phase. They appeared to have no effect on the early phase and maximal(saturated) amplitude of the flash responses.These results supports the idea that decreased cytoplasmic Ca^<2+> concentration may decrease PDE activity and accelerate guanylate cyclase. All substances we tested seemed to make no or little influence on the maximal amplitude of flash responses. This may imply the existence of a mechanism that maintains the free cGMP homeostasis.

已经有相当多的推测认为细胞质Ca 2+ 浓度降低可能在脊椎动物感光器的光适应中发挥作用。为了研究Ca^2+对光转导级联的稳态作用，我们研究了降低的外部Ca^2+浓度、磷酸二酯酶抑制剂(IBMX)和几种鸟苷酸环化酶兴奋剂对青蛙视杆细胞闪光反应的影响。通过将隔离的暗适应棒的内部部分吸入含有林格溶液的玻璃吸管中来记录膜电流。细胞的外节暴露于可改变的浴溶液中。在长时间暴露于1-10μM Ca^2+溶液中(>2分钟)时，闪光反应的潜伏期显着增加并且恢复过程加速。对相对较暗闪光的敏感性降低，但闪光刺激的饱和强度似乎与正常林格溶液中的相同。长时间暴露于 5-50)μM IBMX 溶液会增加闪光反应的潜伏期，并减慢上升和恢复阶段。细胞内的硝普钠和不饱和脂肪酸（花生四烯酸和亚油酸）应用贴片电极仅产生恢复阶段的加速。它们似乎对闪光反应的早期阶段和最大（饱和）幅度没有影响。这些结果支持细胞质Ca ^ 2+ 浓度降低可能降低PDE活性并加速鸟苷酸环化酶的观点。我们测试的所有物质似乎对闪光响应的最大幅度没有影响或影响很小。这可能意味着存在一种维持游离 cGMP 稳态的机制。