Effects of maintained illumination upon [K+]0 in the subretinal space of the frog retina.

Changes in extracellular potassium ion concentration, [K+]0, were measured in the subretinal space of an in vitro preparation of bullfrog retina, pigment epithelium and choroid. In response to maintained illumination [K+]0 fell to a minimum value in 30-40 sec, and then began to recover, reaching a steady-state approximately 10 min after light onset. At light offset, [K+]0 overshot the dark-adapted baseline before recovering. Pigment epithelial membrane potentials followed [K+]0 during this entire timeperiod, causing parallel changes in the d.c. level of the vitreal electroretinogram (ERG). These changes in [K+]0 are very similar to those observed in the cat retina in vivo, except that they are slower in time-course by nearly an order of magnitude. The vitreal ERG, however, is much different in frog than in cat, since in frog, but not in cat, it is an indirect measure of [K+]0 in the subretinal space.