STUDIES ON THE SLOW DEPRESSIVE POTENTIAL OF THE ISOLATED FROG RETINA

Abstract

The slow depressive potential (SDP) was investigated in the isolated frog retina deprived of the pigment epithelium. In this preparation, the SDP could be evoked easily by photic, mechanical or electrical stimulation with applying a 15 m[image] Cl solution on the receptor side and of a Cl-free solution on the vitreous side. The SDP was characterized as a biphasic transretinal dc [direct current] potential change revealing the surface of the receptor side to be negative with respect to that of the vitreous side at first and then positive. The SDP was definitely an ''all-or-none'' response, and was elicited by a dc current across the retina when the electrode on the receptor side was positive. Transretinal impedance decreased during the SDP, and the elevation in conductivity was of the order of 2-4%. The a- and b-wave was affected by the SDP. The b-wave abolished at the peak of the negative potential shift and it had the long recovery time. The effect on the a-wave was not so remarkable as observed on b-wave and it restored its original amplitude when the negative potential shift returned to the original level. An increase of extracellular volume caused by contractions of Muller cells and an increase of K ion concentration in the extracellular space could be expected during the SDP.