[Voltage dependence of the cobalt-induced blockage of synaptic transmission between the photoreceptors and horizontal cells of the retina].

: Synaptic transmission between photoreceptors and horizontal cells (HC) in the turtle retina blocked by Co2+ ions can be restored by constant radial current passed through the retina and depolarizing presynaptic receptor terminals. This result is not related with the action of current on horizontal cells themselves because their depolarization through the intracellular microelectrode did not restore the response to light. The restoring effect of presynaptic depolarization consists of two components: the opening of additional Ca-channels not blocked by Co2+ in the presynaptic membrane, and the voltage-dependence of Co2+ blockade. The latter component can explain such a paradoxical phenomenon as an increase of the horizontal cell response to moderate light stimuli when synaptic transmission is partly blocked by Co2+ ions.