Light-dependent hydration of the space surrounding photoreceptors in the cat retina.
We have studied the effect of retinal illumination on the concentration of the extracellular space marker tetramethylammonium (TMA+) in the dark-adapted cat retina using double-barreled ion-selective microelectrodes. The retina was loaded with TMA+ by a single intravitreal injection. Retinal illumination produced a slow decrease in [TMA+]o, which was maximal in amplitude in the most distal portion of the space surrounding photoreceptors, the subretinal space. The light-evoked decrease in [TMA+]o was considerably slower and of a different overall time course than the light-evoked decrease in [K+]o, also recorded in the subretinal space. [TMA+]o decreased to a peak at 38 s after the onset of illumination, then slowly recovered towards the baseline, and transiently increased following the offset of illumination. It resembled the light-evoked [TMA+]o decreases previously recorded in the in vitro preparations of frog (Huang & Karwoski, 1990, 1992) and chick (Li et al., 1992, 1994) but was considerably larger in amplitude, 22% compared with 7%. As in frog, where it was first recorded, the light-evoked [TMA+]o decrease is considered to originate from a light-evoked increase in the volume of the subretinal space (or subretinal hydration). A mathematical model accounting for [TMA+]o diffusion predicted that the volume increase underlying the response was 63% on average and could be as large as 95% and last for minutes. The estimated volume increase was then used to examine its effect on K+ concentration in the subretinal space. We conclude that a light-dependent hydration of the subretinal space represents a significant physiological event in the intact cat eye, which should affect the organization of the interphotoreceptor matrix, and the concentrations of all ions and metabolites located in the subretinal space.
Li
J D
JD
Department of Physiology, University of California, San Francisco 94143-0444.
Govardovskii
V I
VI
Steinberg
R H
RH
D000818:Animals; D001692:Biological Transport; D002415:Cats; D003623:Dark Adaptation; D004594:Electrophysiology; D005110:Extracellular Space / Q000378:metabolism*; D005731:Ganglionic Stimulants / Q000378:metabolism; D017736:Ion-Selective Electrodes; D010775:Photic Stimulation; D010786:Photoreceptor Cells / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012160:Retina / Q000378:metabolism / Q000502:physiology*
D005731:Ganglionic Stimulants; D000644:Quaternary Ammonium Compounds; C027917:tetramethylammonium; D011188:Potassium