Light activation of phospholipase A2 in the photoreceptor of the crayfish (Procambarus clarkii).
Retinal lipids of crayfish, kept at 4 degrees C under continuous darkness for 3 weeks, consisted mainly of phosphatidylcholine (PC) and phosphatidylethanolamine (PE); sphingomyelin (SM), phosphatidylinositol (PI) and phosphatidylserine (PS) were minor contributors. PI, involved in the phototransduction cascade, never reached greater concentrations than 7% of the total. High concentrations of polyunsaturated fatty acids (PUFA) such as 20:4n-6, 20:5n-3 and 22:6n-3 (DHA, docosahexaenoic acid) were present in PC, PE and PS, but scarce in SM and PI. In retinae of crayfish kept at 4 degrees C in darkness for 3 weeks and then exposed to white light (6 h; ca. 4,500 lx), SM and PS remained seemingly unaffected. PC, however, significantly decreased within 10 min to 65% of the initial value and 50% at 180 min. To study the reduction of PC, lipids of retinae suspended in physiological solution with/without phospholipase C (PLC) and phospholipase A2 (PLA2) inhibitors such as DMDA (= DEDA), manoalide, ET-18-OCH3, and U-73122 were measured. Only free fatty acids (FFA) of retinae with inhibitors of PLA2 like DMDA and manoalide decreased. Retinae irradiated by white light for 3 h displayed a significant reduction of PC, compared with those that had remained in continuous darkness. However, the PC of retinae with PLA2-inhibitors was not decreased by light. Our results provide evidence that not only photoreceptor cell PLC, but also PLA2 is activated by light.
Kashiwagi
T
T
Department of Virology, School of Medicine, Kurume University, Fukuoka, Japan.
Meyer-Rochow
V B
VB
Nishimura
K
K
Eguchi
E
E
D000818:Animals; D003400:Astacoidea; D002462:Cell Membrane / Q000201:enzymology; D003623:Dark Adaptation / Q000502:physiology; D004789:Enzyme Activation / Q000502:physiology; D004963:Estrenes / Q000494:pharmacology; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000378:metabolism / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D010742:Phospholipid Ethers / Q000494:pharmacology; D010775:Photic Stimulation; D017956:Photoreceptor Cells, Invertebrate / Q000187:drug effects / Q000201:enzymology*; D011760:Pyrrolidinones / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology; D014785:Vision, Ocular / Q000502:physiology*
D004963:Estrenes; D005230:Fatty Acids, Nonesterified; D005231:Fatty Acids, Unsaturated; D010713:Phosphatidylcholines; D010726:Phosphodiesterase Inhibitors; D010742:Phospholipid Ethers; D011760:Pyrrolidinones; D013729:Terpenes; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C026659:edelfosine; C059778:7,7-dimethyl-5,8-eicosadienoic acid; C045673:manoalide; D010741:Phospholipases A; D054467:Phospholipases A2