Molecular mechanisms underlying the high temporal resolution of photoreceptors.

点击翻译按钮获取中文摘要

Photo-electric transduction system in photoreceptor cells of higher animals possesses sophisticated characteristics. First is the ability for adaptation against an extraordinarily wide back-ground illumination, and second is a high temporal resolution that allows the system to receipt a photic pulse as a pulse. PI examined the function of an inhibitory subunit of cGMP-phosphodiesterase (g subunit of PDE ; Pg) and its regulatory mechanism to elucidate the molecular mechanism that attributes to the high temporal resolution of photoreceptors. In addition, on the basis of the finding that inositol phospholipids affect the phosphorylation of Pg by an endogenous protein kinase in photoreceptors, PI examined the relationship between the regulatory mechanism of light-dependent cGMP phosphodiesterase and inositol phospholipids metabolizing system in rod photoreceptors.As for the endogenous protein kinase of Pg in rod photoreceptors, its molecular weight was found to be approximately 42-45 kDa and pI value was 5.2. PI could not succeed to obtain its specific antibody nor a clone of its gene for its low content in source organ, though PI obtained new insight in the function of Pg during the examination described above. By this time, the inhibition of the apo-enzyme of phosphodiesterase is the only one function of Pg. However, it was shown that the release of Pg from Pab by binding with transducin results in the release of cGMP from the non catalytic binding site on Pab. This fact suggests that the quick recovery of cGMP after light stimulation of PDE is at least partly attributable to the release of cGMP from Pab. Furthermore, PI found that the inhibitors of inositol phospholipid metabolism (U73122 and neomycin) significantly inhibit light-mediated cGMP hydrolysis in rod photoreceptor outer segments.