Kinetics of bleaching and regeneration of rhodopsin in abnormal (RCS) and normal albino rats in vivo.

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Abstract
Rhodopsin concentration was measured by densitometry in retinae of rats with inherited retinal dystrophy (RCS [Royal College of Surgeons]) raised in darkness, and was compared with that of normal rats similarly reared. In RCS and normal rats the fraction of rhodopsin bleached was always directly proportional to the photon content of the light, I.t, where I is the light intensity in effective quanta (500 nm) per square centimeter per second and t is the duration of the bleaching exposure in seconds. Rhodopsin photosensitivity for bleaching was slightly higher in RCS rats than in normals (2.3 (10)-16 cm2 chromophore-1 compared with 1.3 (10)-16 cm2 chromophore-1). Rhodopsin regeneration in the dark in RCS and normal rats could not be described by the kinetics of a simple monomolecular chemical reaction. Following 5 min bleaches, the regeneration rate became slower as the preceding bleach was made stronger. Regeneration in the dark was significantly faster in RCS rats than in normal rats. In normal rats, after a full bleach, rhodopsin regenerated back to the dark-adapted level within 3-4 h. In RCS rats rhodopsin regenerated to reach a plateau level, below the previous dark-adapted level, that lasts for several hours. The faction of total rhodopsin that could regenerate gradually declined with age until in 70 day old RCS rats no rhodopsin regeneration could be measured by the densitometer. Total rhodopsin density (fully bleached-dark-adapted) was still close to normal.

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