MECHANISM OF THE SLOW DEPRESSIVE POTENTIAL PRODUCTION IN THE ISOLATED FROG RETINA

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Abstract
The mechanism of the slow depressive potential (SD) production was investigated with the isolated frog retina deprived of the pigment epithe -lium. Both the latency and the amplitude of the b-wave were affected by the evolution of the SDP. A decrease in amplitude and an increase in latency were observed during the development of the SDP. Reduction of Na or Mg in the bathing solution did not affect significantly both the amplitude of the SDP and the b-wave latency. Exposing the retina to the Ca-free solution, the amplitude of the SDP was decreased and the b-wave latency was lengthened gradually. Lowering the K concentration on the receptor side caused an increase, on the contrary, raising the K concentration a decrease in amplitude of the SDP. There was a logarithmic relation between the amplitude of the SDP and K concentration in the bathing solution. Whereas, raising the K concentration on the receptor side led to an increase in the b-wave latency. The ratio of E1 and E2 of the SDP remained constant even if various cation concentrations in the bathing solutions were modified. The SDP induced by a light stimulus was interpreted as the summed response of the negative response and the positive response. The SDP is apparently generated most probably by the Miiller cell as a depolarization of a cell membrane except that forming the so-called inner limiting membrane.