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 Retinal Cones and Rods: resolution to Intense I. Korenbrot Department of Physiology, School of Medicine, University of atomic number 20 at San Francisco, San Francisco, California 94143 Cone photoreceptors are less natural to visible radiation and the duration of their photo repartee is shorter than that of rods. In salamander rods and cones, we identify 3 components in membrane currents activated by in behinddescence flashes of light: an early receptor current (ERC) resulting from charge extirpation within visual pigments, a fertilisation photocurrent generated by the pulley of the cGMP-sensitive channels, and a putative Na-Ca exchanger current. The epoch courses of both the ERC and the blast of the saturation photocurrent were similar in rods and cones. The putative Na-Ca exchanger current, on the different hand, is 4- to 8-fold immediateer in cones. The onset of the saturation photocurrent consisted of a stick about on followed by a fast relaxation with an exponential cartridge holder course.

In both photoreceptor types the delay and the clip course of the fast relaxation are dependent on light impregnation and reach a limiting harbor 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 about identical in rods and cones. The near identity of these parameters implies that at least 2 energising steps in the activation respons e of rods and cones are quantitatively simil! ar. These findings suggest that the structural differences between rods and cones whitethorn arise from disparities in the processes that restore the components of the phototransduction cascade to their dark direct and not from differences in the activation processes. The visual systemof man can detect singlephotons in darkness and yet remain functional under bright lights (Rodieck, 1973). This flexible performance...If you want to get a full essay, secern it on our website: OrderCustomPaper.com

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