INCREASE IN SENSITIVITY FOLLOWING LIGHT ILLUMINATION IN FROG PHOTORECEPTORS

Dark-adaptation of photoreceptors was studied by recording fast PIII responses of the isolated bull frog retina superfused with Conway's solution containing 5 mM sodium aspartate. When a dark-adapted retina is illuminated by an adapting light, the amplitude of the response decreases. Initially on turning off this light, the amplitude increases over that of the dark-adapted response. This phenomenon, hypersensitivity" is thought to be due to an increase in sensitivity of red rods. The hypersensitivity occurs following several minutes illumination with relatively weak light if [Ca2+ out] is low. Intense light and higher concentration of Ca2+ inhibit the hypersensitivity. Possible mechanisms for the hypersensitivity are discussed. © 1979."