The role of zinc in the dark-adapted retina studied directly using microPIXE

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 b ut it is likely that zinc plays a unique role in the phototransduction proc ess and/or photoreceptor/retinal pigment interaction. The localisation of f ree (histochemically reactive) zinc within the photoreceptors changes with light stimulation [Exp. Eye Res. (1999) 459]. In the dark-adapted retina ch elatable zinc can be visualised primarily in the perikarya, whereas after p hotostimulation free zinc is mainly associated with the inner segments. Thi s 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 wa s used to analyse the total (free and bound) zinc distribution in each reti nal layer and a difference was found between light- and dark-adapted retina s (preliminary data). Following light stimulation the most pronounced diffe rence in the zinc concentration was found in the inner segments of the phot oreceptors and the layer containing the photoreceptors perikarya (outer nuc lear layer). (C) 2001 Elsevier Science B.V. All rights reserved.