Abstract
Zinc deficiency is known to cause night blindness, which can be reverted by the administration of zinc. The exact function of zinc is not understood but it is likely that zinc plays a unique role in the phototransduction process and/or photoreceptor/retinal pigment interaction. The localisation of free (histochemically reactive) zinc within the photoreceptors changes with light stimulation [Exp. Eye Res. (1999) 459]. In the dark-adapted retina chelatable zinc can be visualised primarily in the perikarya, whereas after photostimulation free zinc is mainly associated with the inner segments. This variation might be due to (1) a translocation of zinc from the perikarya to the inner segments, (2) a change in the state of zinc (from a free to a bound form, histochemically and non-histochemically reactive, respectively), or (3) zinc influx and/or efflux across the plasma membrane. MicroPIXE was used to analyse the total (free and bound) zinc distribution in each retinal layer and a difference was found between light- and dark-adapted retinas (preliminary data). Following light stimulation the most pronounced difference in the zinc concentration was found in the inner segments of the photoreceptors and the layer containing the photoreceptors perikarya (outer nuclear layer).
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