DECREASED ENERGY REQUIREMENT OF TOAD RETINA DURING LIGHT ADAPTATION AS DEMONSTRATED BY P-31 NUCLEAR-MAGNETIC-RESONANCE

1. The effect of light and dark adaptation on the levels of phosphorus metabolites (nucleotide di- and triphosphates, phosphocreatine, pyrid ine nucleotide, inorganic phosphate, phosphodiesters, phosphomonoester s, and uridine diphosphate-glucose) in the toad (Bufo marinus) retina and retinal extracts was studied by P-31 nuclear magnetic resonance (N MR) spectroscopy. 2. Spectra were acquired using an NMR probe specific ally designed for superfusion and illumination of a single retina. Ret inae were maintained at a steady state for up to 10 h in an electrolyt e solution containing 10 mm Hepes buffer and bubbled with 98% O2-2% CO 2, pH 7.8 at 20-degrees-C. 3. The intracellular concentrations of the phosphorus metabolites were measured in total darkness or during prolo nged exposure to light. The concentration of nucleoside triphosphates (NTP) in the dark-adapted retina was about 1.5 mm and that of phosphoc reatine (PCr) was about 0.7 mm. 4. In saturating levels of light, 6.0 x 10(11) or 1.5 x 10(13) quanta s-1 cm-2 at 520 nm, the levels of PCr and phosphomonoesters rose, the levels of NTP and protons (pH) were ma intained, and the levels of pyridine nucleotides and nucleotide diphos phates (NDP) fell. 5. A rise in the level of PCr in the presence of an unchanged level of NTP in the light-adapted retina indicates that the energy consumption of the retina is greater in the dark. 6. These res ults are in agreement with the results of oxygen consumption, glucose dependence, and electrophysiological studies which also indicate that the metabolic energy requirement of the retina decreases in light.