Activation kinetics of retinal cones and rods: response to intense flashes of light. 1990

S Hestrin, and J I Korenbrot
Department of Physiology, School of Medicine, University of California, San Francisco 94143.

Cone photoreceptors are less sensitive to light and the duration of their photoresponse is shorter than that of rods. In salamander rods and cones, we identified 3 components in membrane currents activated by bright flashes of light: an early receptor current (ERC) resulting from charge displacement within visual pigments, a saturation photocurrent generated by the closure of the cGMP-sensitive channels, and a putative Na-Ca exchanger current. The time courses of both the ERC and the onset of the saturation photocurrent were similar in rods and cones. The putative Na-Ca exchanger current, on the other hand, is 4- to 8-fold faster in cones. The onset of the saturation photocurrent consisted of a delay followed by a fast relaxation with an exponential time course. In both photoreceptor types the delay and the time course of the fast relaxation are dependent on light intensity and reach a limiting value when about 1% of the photopigment is bleached. The limiting value of the delay, about 8 msec, and of the relaxation time constant, about 2 msec, are nearly identical in rods and cones. The near identity of these parameters implies that at least 2 kinetic steps in the activation response of rods and cones are quantitatively similar. These findings suggest that the functional differences between rods and cones may arise from disparities in the processes that restore the components of the phototransduction cascade to their dark level and not from differences in the activation processes.

UI MeSH Term Description Entries
D007700 Kinetics The rate dynamics in chemical or physical systems.
D007814 Larva Wormlike or grublike stage, following the egg in the life cycle of insects, worms, and other metamorphosing animals. Maggots,Tadpoles,Larvae,Maggot,Tadpole
D010775 Photic Stimulation Investigative technique commonly used during ELECTROENCEPHALOGRAPHY in which a series of bright light flashes or visual patterns are used to elicit brain activity. Stimulation, Photic,Visual Stimulation,Photic Stimulations,Stimulation, Visual,Stimulations, Photic,Stimulations, Visual,Visual Stimulations
D010786 Photoreceptor Cells Specialized cells that detect and transduce light. They are classified into two types based on their light reception structure, the ciliary photoreceptors and the rhabdomeric photoreceptors with MICROVILLI. Ciliary photoreceptor cells use OPSINS that activate a PHOSPHODIESTERASE phosphodiesterase cascade. Rhabdomeric photoreceptor cells use opsins that activate a PHOSPHOLIPASE C cascade. Ciliary Photoreceptor Cells,Ciliary Photoreceptors,Rhabdomeric Photoreceptor Cells,Rhabdomeric Photoreceptors,Cell, Ciliary Photoreceptor,Cell, Photoreceptor,Cell, Rhabdomeric Photoreceptor,Cells, Ciliary Photoreceptor,Cells, Photoreceptor,Cells, Rhabdomeric Photoreceptor,Ciliary Photoreceptor,Ciliary Photoreceptor Cell,Photoreceptor Cell,Photoreceptor Cell, Ciliary,Photoreceptor Cell, Rhabdomeric,Photoreceptor Cells, Ciliary,Photoreceptor Cells, Rhabdomeric,Photoreceptor, Ciliary,Photoreceptor, Rhabdomeric,Photoreceptors, Ciliary,Photoreceptors, Rhabdomeric,Rhabdomeric Photoreceptor,Rhabdomeric Photoreceptor Cell
D004594 Electrophysiology The study of the generation and behavior of electrical charges in living organisms particularly the nervous system and the effects of electricity on living organisms.
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D014562 Urodela An order of the Amphibia class which includes salamanders and newts. They are characterized by usually having slim bodies and tails, four limbs of about equal size (except in Sirenidae), and a reduction in skull bones. Amphiuma,Caudata,Eel, Congo,Salamanders,Congo Eel,Congo Eels,Eels, Congo,Salamander

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