Temporal kinetics of the light/dark translocation andcompartmentation of arrestin and α-transducin in mousephotoreceptor cells

[摘要] Purpose: To determine the temporal kinetics of the simultaneoustranslocation of arrestin and rod α-transducin in mice exposed todifferent lighting environments and to compare the subcellularcompartmentation of cone α-transducin with arrestin.Methods: Double labeling immunofluorescence microscopy and imageanalysis are used to visualize and quantify the concentrations of rodarrestin and α-transducin in the subcellular compartments of therod outer segments, the rod inner segments and the synaptic terminals.Results: The magnitude of the effects of the translocation areclearly contrasted in images of the retinas of animals that have beenmaximally light adapted verses retinas that have been maximally darkadapted. The onset of light results in a rapid, simultaneous,translocation of arrestin and α-transducin from their respectivecompartments (α-transducin in the rod outer segment and arrestin inthe rod inner segment) to the opposite compartment. Almost all ofα-transducin has translocated in less than two min whereas thetranslocation of the majority of arrestin requires at least five to sixmin. Translocation in the opposite direction, from light to dark, occursmore slowly for both proteins with arrestin requiring almost 30 min andα-T needing more than 200 min to complete its journey. Under thesame lighting conditions, cone arrestin translocation is incomplete.Cone α-transducin does not translocate under any the lightingconditions tested. Unlike the frog, continuous exposure of mice to lightdoes not result in arrestin translocating back to the rod innersegment.Conclusions: These data suggest that there are four mechanismsinvolved in the translocation of these two proteins. They also supportthe conclusion that the more important cellular function of thetranslocation process is to terminate phototransduction in rod and conephotoreceptors, which could provide protection against light damage. Thesecondary function of translocation is to maximize rod sensitivity tolight during dark adaptation. The restricted localization of coneα-transducin to the cone outer segment is consistent with thefunction of cones in bright light, just as the concentration of rodα-transducin in dark adapted rod outer segment is consistent withtheir functioning in dim light.

[学科分类] 生物化学/生物物理