From candelas to photoisomerizations in the mouse eye by rhodopsin bleaching in situ and the light-rearing dependence of the major components of the mouse ERG
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Abstract
To quantify the rate at which light in a ganzfeld produces photoisomerizations in
mouse rods in situ, we measured the rate of rhodopsin bleaching in eyes of recently
euthanized mice with fully dilated pupils. The amount of rhodopsin declined as a first-order
(exponential) function of the duration of the exposure at the luminance of 920 scot
cd m(-2): the rate constants of bleaching were 8.3 x 10(-6) and 2.8 x 10(-5) s(-1)
(scot cd(-1)m2)(-1) for C57B1/6 and 129P3/J mice, respectively. When the approximately
3-fold difference in effective areas of the pupils of the mice are taken into consideration,
the bleaching rates for both strains become essentially the same, 2.6 x 10(-6) fraction
rhodopsin (scot Td s)(-1). Assuming 7 x 10(7) rhodopsin molecules per rod, this bleaching
rate yields the result that a flash of 1 scot Td s produces 181 photoisomerizations
per rod, a value close to that derived from analysis of the collecting area of the
rod for axially propagating light. We measured the electroretinograms of mice of the
two strains reared under controlled illumination conditions (2 and 100 lux), and compared
their properties, using the calibrations to determine the absolute sensitivities of
the b-wave and a-waves. The intensity that produces a half-saturating rod b-wave response
is 0.3-0.6 photoisomerizations rod(-1), and the amplification constant of the rod
a-wave is 5-6 s(-2) photoisomerization(-1), with little dependence on the strain.