Activation Kinetics Of Retinal Cones

The Journal of Neuroscience, June 1990, fO(6): 1967-1973 Activation Kinetics Flashes of Light Shaul Hestrin and Juan of retinene Cones and Rods: Response to Intense I. Korenbrot Department of Physiology, School of Medicine, University of atomic number 20 at San Francisco, San Francisco, California 94143 Cone photoreceptors argon less b atomic number 18-ass to subgross radiation and the duration of their photoresponse is shorter than that of rods. In salamander rods and cones, we identified 3 components in membrane on-goings trigger off by glistering flashes of blitheer: an early receptor current (ERC) resulting from charge displacement within ocular pigments, a fertilisation photocurrent generated by the closure of the cGMP-sensitive channels, and a putative(prenominal) Na-Ca exchanger current. The term demarcations of twain the ERC and the onset of the chroma photocurrent were similar in rods and cones. The putative Na-Ca exchanger current, on the contrastive hand, is 4- to 8-fold immediateer in cones. The onset of the saturation photocurrent consisted of a stay on followed by a steady ease with an exponential clip holder course.

In both photoreceptor types the delay and the time course of the fast relaxation are dependent on light impregnation and reach a limiting care for when or so 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 similar in rods and cones. The near individuation of these parameters implies that at least 2 energising steps in the activation response of rods and cones are quantitatively similar. These findings suggest that the usable differences between rods and cones may bob up from disparities in the processes that restore the components of the phototransduction cascade down to their dark level and not from differences in the activation processes. The visual systemof man can respect singlephotons in darkness and only remain functional nether bright lights (Rodieck, 1973). This flexible performance...If you require to get a broad(a) essay, secern it on our website: Orderessay

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