Otto-Bruc A, Fariss R N, Haeseleer F, Huang J, Buczyłko J, Surgucheva I, Baehr W, Milam A H, Palczewski K
Department of Ophthalmology, School of Medicine, University of Washington, Seattle, WA 98195, USA.
Proc Natl Acad Sci U S A. 1997 Apr 29;94(9):4727-32. doi: 10.1073/pnas.94.9.4727.
Guanylate cyclase-activating proteins (GCAP1 and GCAP2) are thought to mediate the intracellular stimulation of guanylate cyclase (GC) by Ca2+, a key event in recovery of the dark state of rod photoreceptors after exposure to light. GCAP1 has been localized to rod and cone outer segments, the sites of phototransduction, and to photoreceptor synaptic terminals and some cone somata. We used in situ hybridization and immunocytochemistry to localize GCAP2 in human, monkey, and bovine retinas. In human and monkey retinas, the most intense immunolabeling with anti-GCAP2 antibodies was in the cone inner segments, somata, and synaptic terminals and, to a lesser degree, in rod inner segments and inner retinal neurons. In bovine retina, the most intense immunolabeling was in the rod inner segments, with weaker labeling of cone myoids, somata, and synapses. By using a GCAP2-specific antibody in enzymatic assays, we confirmed that GCAP1 but not GCAP2 is the major component that stimulates GC in bovine rod outer segment homogenates. These results suggest that although GCAP1 is involved in the Ca2+-sensitive regulation of GC in rod and cone outer segments, GCAP2 may have non-phototransduction functions in photoreceptors and inner retinal neurons.
鸟苷酸环化酶激活蛋白（GCAP1和GCAP2）被认为介导Ca2+对鸟苷酸环化酶（GC）的细胞内刺激，这是视杆光感受器在光照后恢复暗状态的关键事件。GCAP1已被定位到视杆和视锥的外段，即光转导的部位，以及光感受器突触终末和一些视锥细胞体。我们使用原位杂交和免疫细胞化学方法在人、猴和牛的视网膜中定位GCAP2。在人和猴的视网膜中，抗GCAP2抗体的最强免疫标记出现在视锥细胞的内段、细胞体和突触终末，在视杆细胞内段和视网膜内层神经元中的标记程度较低。在牛视网膜中，最强的免疫标记出现在视杆细胞内段，视锥肌样体、细胞体和突触的标记较弱。通过在酶促测定中使用GCAP2特异性抗体，我们证实GCAP1而非GCAP2是刺激牛视杆外段匀浆中GC的主要成分。这些结果表明，尽管GCAP1参与视杆和视锥外段中GC的Ca2+敏感调节，但GCAP2可能在光感受器和视网膜内层神经元中具有非光转导功能。
