Retina glycerolipids

NEOBIOSYNTHESIS OF PHOSPHATIDYLINOSITOL AND OF OTHER GLYCEROLIPIDS IN THE ENTIRE CATTLE RETINA... 

ACYL GROUPS, MOLECULAR SPECIES, AND LABELING BY Cr-GLYCEROL AND H-ARACHIDONIC ACID OF VERTEBRATE RETINA GLYCEROLIPIDS... 

The fatty acid composition of toad brain and retina glycerolipids is comparatively presented in Fig. 1. The toad brain lipids, although being more unsaturated as expected for a poikilotherm, share the general features known to be present in mammalian brain high concentration of arachidonate in PI and PE, and of docosahexaenoate in PS,... 

Fig. 1. Fatty acid distribution in toad brain (0) and retina (0) glycerolipids.

Large quantities of docosahexaenoate are present in all retina glycerolipids, due to the contribution of lipids from the outer segments of photoreceptors, which are known to be enriched in this fatty acid. However, the same holds for diacylglycerols and phosphatidic acid, which likely are not concentrated in these structures. The unusual composition of these intermediates suggests that an important proportion of toad retinal lipid metabolism may be involved in supporting photoreceptor lipid composition. The concentration of both DG and PA is 4-5 fold higher in the toad than in the cattle retina (Aveldaho Bazan, 1974 and unpublished). 

Table 1. Fatty acid composition of cattle retina glycerolipids.

To inquire about the relations among some glycerolipids in the cattle retina we undertook a time-course study on the simultaneous uptake of C-glycerol and H-arachidonic acid. A comparison is made with the toad (Table 2). The specific activities of cattle retina lipids show a rapid labeling by glycerol of PA at 5 min incubation, followed by a steadily increasing accumulation of label in the other lipids, particularly diacyl- and triacylglycerols. 

Table 3. Distribution of radioactivity from C-glycerol and H-arachidonic acid among retina glycerolipids after 30 min incubation (%)...

EFFECTS OF DIVALENT CATIONS, K+, AND X-537A ON GLYCEROLIPID METABOLISM IN THE CATTLE RETINA... 

The shifts in ion concentration may alter the lipid labeling by either a secondary effect or a direct action on the metabolic steps. In either case, the early time-course of the labeling suggests that the precursor can enter different pools of retina lipids and that different branches of the de novo biosynthesis of retina glycerolipids are very sensitive to shifts in the ionic environment. Further experiments with lower concentrations of X-537A as well as with another carboxylic acid lipid soluble ionophore will likely help in clarifying the dual effect shown here to be exerted by this antibiotic. 

EFFECTS OF TEMPERATURE, IONIC ENVIRONMENT, AND LIGHT FLASHES ON THE GLYCEROLIPID NEOSYNTHESIS IN THE TOAD RETINA... 

An active glycerolipid synthesis from C-glycerol, predominantly phosphatidylinositol formation, takes place in the toad retina both in vivo and in vitro (Bazan Bazan, 1976). To further study this process a survey of different incubating conditions was carried out. These included variations in temperature, the use of different ionic environments, and the action of a divalent ionophore. In addition it was of particular interest to inquire about the effect of the physiological stimulus of the retina, the light, on the de novo biosynthesis of lipids from C-glycerol in the entire toad retina. 

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