Purchase this article with an account.
D. C. Mitchell, S.-L. Niu, M. Bennett, L. A. Greeley, K. G. Hines, B. M. Andersen; Effects of ROS Disk Membrane Phospholipids With Extremely Long Polyunsaturated Acyl Chains on Visual Signalling. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2928.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Phospholipids with extremely long chain polyunsaturated fatty acids (ELCPs) consist of 26 to 36 carbons. In rod outer segment disk membranes they comprise 10% to 30% of the phosphatidylcholine (PC) species. The possible impact of these ELCPs in visual signal transduction is unknown. To determine the manner in which ELCPs alter membrane stability and acyl chain packing and determine the effects of ELCPs on receptor function and G protein-coupled signal transduction within the rod outer segment.
Normal phase HPLC was used to isolate a PC fraction of disk membrane phospholipids that was greater than 95% ELCP. ELCP-PC was mixed with varying amounts of 18:0,18:1PC in pure lipid vesicles and reconstituted with rhodopsin, transducin and phosphodiesterase (PDE). Rhodopsin activation, transducin binding, PDE activity, acyl chain packing, and both membrane and protein thermal stability were examined.
Preliminary molecular characterization of the ELCP-PC fraction with capillary MS/MS showed that 50% of the acyl chains are 22:6n-3, about 30% are 32 carbon species and about 15% are 34 carbon species. In pure lipid bilayers increasing levels of ELCP-PC slightly disordered acyl chain packing and reduced the thermal stability of 18:0,18:1PC. Detailed examination of acyl chain packing demonstrated that the 32 and 34 carbon acyl chains do not extend from one bilayer leaflet, across the bilayer midplane into the opposite bilayer leaflet. This suggests that the ELCP acyl chains curl up in a manner similar to that recently demonstrated for docosahexaenoic acid(DHA). Increasing levels of ELCP-PC greatly enhanced formation of the active MII sate of rhodopsin. However, 40% ELCP-PC in 18:0,18:1PC lowered PDE activity by 50% at physiological levels of stimulus.
Large increases in rhodopsin activation coupled with modest relaxation in acyl chain packing suggest that ELCP-PC promotes rhodopsin activation via direct interaction rather than via changes in acyl chain packing. The reduction in PDE activity in spite of increased rhodopsin activation at high levels of ELCP-PC suggests that optimal functioning of GPCR signaling may require an optimal level of ELCP.
This PDF is available to Subscribers Only