Reactive oxygen species uncouple external horizontal cells in the carp retina and glutathione couples them again

We have investigated the effect of free radicals on the electrical gap junc tions between horizontal cells in the carp retina. In our previous study, L -buthionine sulfoximine. an inhibitor of glutathione synthesis. caused unco upling of horizontal cells four days after injection. In the present study, we have used paraquat, a generator of exogenous reactive oxygen species, t o investigate whether it was the depletion of glutathione or an increase in the level of reactive oxygen species which resulted in horizontal cell unc oupling after L-buthionine sulfoximine injection. Intracellular recordings were made from L-type horizontal cells at various time-points after intravi treal injection of paraquat. Injection of 25 nmol paraquat caused an increa se in response amplitude to central spot light stimuli by two days after in jection, which continued for a further two to three days and had almost dis appeared by seven days after injection. There was also a sharp increase in reactive oxygen species production, peaking at four days and disappearing b y seven days after injection, and an accompanying depletion and a restorati on of glutathione levels with a similar rims-course. Marking cells with Luc ifer Yellow clearly illustrated uncoupling of horizontal cells after paraqu at injection. If paraquat and L-buthionine sulfoximine were injected simult aneously, the increase in response to central spots was observed as early a s one day after injection. This response amplitude was not more enhanced th an that observed after L-buthionine sulfoximine injection alone, although a dramatic increase in the level of reactive oxygen species was observed. From these results. we suggest that reactive oxygen species are involved in uncoupling. while recovery from uncoupling is dependent on glutathione. Fu rthermore, we conclude that a balance between glutathione and reactive oxyg en species levels is the most important Factor controlling gap junctional i ntercellular communication of L-type horizontal cells in the carp retina. ( C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.