THE C-WAVE OF THE ELECTRORETINOGRAM POSSESSES A 3RD COMPONENT FROM THE PROXIMAL RETINA

ERG and light-induced extracellular potassium ([K+](o)) changes have b een measured in isolated retinas of both Rana esculenta and Rana tempo raria. The conditions of the preparations have been varied. Isolated f rog retinas kept receptor side-upward in a moist chamber without perfu sion showed the well-known slow PIII in the ERG. Retinas superfused fr om the receptor side, with O-2 enrichment at their vitreal surface, ho wever, exhibit a slow cornea-positive potential in the ERG. The slow E RG-potentials relate to different light-induced potassium changes in t he proximal retina. There was a long lasting and larger proximal potas sium increase in adequately maintained retinas but a smaller and short er one in preparations lacking superfusion and oxygen. There was no si gnificant difference between the size of potassium decrease around rec eptors of retinas superfused from their vitreal side and those superfu sed from receptor side. A reduction of slow PIII should therefore not be responsible for the slow cornea-positive potential. The long lastin g and larger (by 59%) potassium increase in the proximal retina may co unteract the potential in the Muller cells caused by the potassium dec rease around receptors and thereby cancel slow PIII and generate a thi rd component of the electroretinogram c-wave.