High cGMP synthetic activity in carp cones
High cGMP synthetic activity in carp cones
复制标题
DOI：
10.1073/pnas.0812781106
复制
发表时间：
2009-07-14
影响因子：
11.1
通讯作者：
Kawamura, Satoru
中科院分区：
文献类型：
--
作者：
Takemoto, Norihiko;Tachibanaki, Shuji;Kawamura, Satoru
视锥细胞的光反应比视杆细胞更短，即使在非常亮的光下也不会饱和。使用纯化的视杆和视锥匀浆，我们测量了鸟苷酸环化酶 (GC) 的活性，这种酶负责 cGMP 合成，从而恢复光响应。视锥细胞中的基础GC活性比视杆细胞中高36倍：这主要是由于视锥细胞（GC-C）中的GC表达水平高于视杆细胞（GC-R）中的GC表达水平所致。通过对视杆细胞和视锥细胞中表达的 GC 激活蛋白 (GCAP) 亚型的鉴定和定量，以及在存在和不存在 GCAP 的情况下确定 GC 激活的动力学参数，我们估计了低和高 Ca2+ 浓度下视杆细胞和视锥细胞中的原位 GC 活性。研究表明，在暗适应和光适应状态下，视锥细胞的 GC 活性均比视杆细胞高 10 倍以上。在杆状和锥状外节的截短制剂中测量的 GC 活性的电生理学估计给出了一致的结果。我们对原位 GC 活性的估计合理地解释了锥光响应的快速恢复和非饱和行为。
Cones show briefer light responses than rods and do not saturate even under very bright light. Using purified rod and cone homogenates, we measured the activity of guanylate cyclase (GC), an enzyme responsible for cGMP synthesis and therefore recovery of a light response. The basal GC activity was 36 times higher in cones than in rods: It was mainly caused by higher expression levels of GC in cones (GC-C) than in rods (GC-R). With identification and quantification of GC-activating protein (GCAP) subtypes expressed in rods and cones together with determination of kinetic parameters of GC activation in the presence and absence of GCAP, we estimated the in situ GC activity in rods and cones at low and high Ca2+ concentrations. It was revealed that the GC activity would be > 10 times higher in cones than in rods in both the dark-adapted and the light-adapted states. Electrophysiological estimation of the GC activity measured in the truncated preparations of rod and cone outer segments gave consistent results. Our estimation of the in situ GC activity reasonably explained the rapid recovery and nonsaturating behavior of cone light responses.