Effects of hypoxia and post-hypoxic recovery on chick retinal pigment epithelium potentials and light-evoked responses in vitro.
OBJECTIVE
To determine the cellular mechanisms involved in the hypoxia-induced alteration of the retinal pigment epithelium (RPE) potentials and the light-evoked responses of the RPE in chicks. In addition, to determine the mechanisms involved in the recovery of the RPE during the post-hypoxic period.


METHODS
In vitro preparations of chick retina-RPE-choroid were studied by potassium-selective microelectrodes placed in the subretinal space. In addition, single-barrel microelectrodes were used to obtain intracellular recordings from the RPE cells. The perfusate was bubbled continuously with 95% oxygen and 5% carbon dioxide for the control condition and replaced by 95% nitrogen and 5% carbon dioxide to induce hypoxia.


RESULTS
Hypoxia induced a significant reduction of the trans-tissue potential which was found to result from the depolarization of the apical membrane of the RPE. This depolarization was induced by an increase of subretinal [K+]o. The c-wave was also markedly decreased or abolished during hypoxia. There were two phases of post-hypoxic recovery: an initial small increase in the trans-tissue potential resulting from a basal membrane depolarization followed by an apical membrane hyperpolarization. The trans-tissue potential and the c-wave also were supernormal in two phases during this post-hypoxic period. The c-wave amplitude was temporarily elevated (263.7 +/- 77.4% of pre-hypoxic control) because of the enhanced trans-epithelial c-wave and without a light-evoked decrease in subretinal [K+]o.


CONCLUSIONS
The trans-tissue potential and the c-wave were markedly decreased during hypoxia. During the post-hypoxic period, both potential recovered with transient supernormalities in two phases. The results suggested that the hypoxic changes resulted directly from changes of the RPE membranes and indirectly from a change in the subretinal [K+]o but were not mediated by the light-evoked decrease in subretinal [K+]o.
Nakazaki
S
S
Department of Ophthalmology, Miyazaki Medical College, Japan. shujina@postl.miyazaki-med.ac.jp
Nao-i
N
N
Sawada
A
A
D000818:Animals; D015687:Cell Hypoxia; D002645:Chickens; D017097:Electric Impedance; D004594:Electrophysiology; D066298:In Vitro Techniques; D008027:Light; D010100:Oxygen / Q000502:physiology*; D010857:Pigment Epithelium of Eye / Q000502:physiology* / Q000528:radiation effects*; D012160:Retina / Q000502:physiology* / Q000528:radiation effects*
D010100:Oxygen