Ionic mechanisms underlying the center and surround responses of on-center bipolar cells in the carp retina.

Reversal potentials were measured for the center and surround responses of on-center bipolar cells in the carp retina. In the scotopic condition, the center response showed a reversal at 29 +/- 13mV, the surround response at 38 +/- 13 mV. The result suggests that both the center and surround responses were -53 +/- 11 mV and -59 +/- 11 mV, respectively. These responses were sensitive to the red light. It is therefore suggested that both the center and surround responses contributed by rods are mediated by changes in conductance of Na+ channels but in opposite ways. In the photopic condition, reversal potentials of the center and surround responses contributed by red cones are mediated by changes in conductance of K+ and/or Cl- channels, but in opposite ways. The responses in the mesopic condition showed the complex electrical properties as a consequence of interaction between the two ionic components described above.