LIGHT‐INDUCED ALTERATIONS IN RETINAL PYRUVATE AND HIGH‐ENERGY PHOSPHATES, IN VIVO

—The effect of illumination upon some metabolic substrates of frog retina was investigated in vivo, using conditions of illumination for which electrophysiological correlates in the retina are well defined. Frogs were frozen immediately after illumination, the tissue was processed for quantitative histochemistry, and the compounds were measured fluorometrically. Levels of P‐creatine were lower in flash‐illuminated retinas than in either dark‐ or light‐adapted retinas. The high‐energy phosphates and pyruvate changed rapidly upon exposure to flashing light, then returned towards the original steady‐state level, with ATP preceding pyruvate and P‐creatine. ATP and P‐creatine were primarily concentrated in the bipolar and ganglion cell layers. The energy reserve of the retina was depleted by an enhanced rate of neural activity in vivo. Levels of P‐creatine and ATP decreased in only those cellular layers which initiate neural action potentials. These data suggest that the mechanisms of neural excitation are closely coupled to energy and glucose metabolism in the retina.