A new cornea-positive component to the ERG of the aspartate-treated frog retina?

Using isolated bullfrog retinas treated with aspartate, we have found a new cornea-positive photo-response (positive response). The positive response could be detected only when the retina was stimulated by a dim flash. The peak amplitude and the rate of initial rise of the positive response were intensity dependent. The spectral sensitivity of the positive response peaked at 500 nm. The general characteristics of the response were different from those of the PIII response. The positive response was closely related to the extracellular Na+ and Ca2+ concentration and completely abolished by 50 microM La3+. On the basis of the present findings, it was suggested that some types of calcium channels or transporters are involved in the generation of the positive response.