Light potentiation of horizontal cells in the isolated rabbit retina

When the retinas of some fishes and amphibians are dark-adapted the hyperpo larising response of horizontal cells (HCs) to a light stimulus is suppress ed (; dark suppression) but is restored to that of light adaptation when a light stimulus is rapidly repeated (= light potentiation (LP). This phenome non, which had not been previously demonstrated in a mammal, has been recor ded from isolated rabbit retinas. The steady amount of LP of HCs after seve ral light stimuli was expressed as the percentage of induced hyperpolarisat ion when that of the dark-adapted retina is taken as 100%. The LP was small (113+/-13%, n=14), when the HCs had stable and large responses (>15 mV), b ut varied greatly between HCs. Those HCs with slight LP (106+/-3% n=8) desi gnated as x-HCs, mostly exhibited larger overshoots than did those HCs with stronger LP (123+/-14, n=6) and designated y-HCs. These mostly had a small er overshoot. Other HCs (z-HCs) were unstable and were only slightly hyperp olarised by the first light stimulus after dark adaptation but showed the s trongest LP (193+/-48%, n=7). These results could indicate a variable degre e of light potentiation in normally-functioning HCs, which can be classifie d accordingly. It is possible, however, that the degree of LP is small in a ll normally-functioning HCs, but as the HCs in isolated mammalian retinal p reparations deteriorate, the phenomenon of LP is progressively exaggerated. LP is not peculiar to HCs and can also occur in cells which depolarise in response to a light stimulus, and can be evident in the PIII component of t he ERG.