Activation of a regenerative calcium conductance in turtle cones by peripheral stimulation

Abstract
Light stimulation of the periphery of the receptive field of some turtle [Pseudemys scripta elegans] cones evoked spikes which are tetrodotoxin-insensitive. In all cones, Sr2+ or Ba2+ (4-12 mM) induced the appearance of spikes in response to peripheral illumination. These spikes were blocked by Co2+ and by agents which depolarized the L-horizontal cells and blocked their responses. Apparently peripheral illumination evokes Ca2+ spikes in turtle cones through a feedback synaptic mechanism from the L-horizontal cells.