Fig. 1.

Light-elicited decrease in average Ca²⁺ in cone terminals. (A-D) Images from two-photon scans of OPL of a flat-mounted anole retina loaded with the Ca²⁺ dye OGB-1. To reveal the decrease in Ca²⁺ resulting from light, scans were taken from dark-adapted retina before (A) and after (B) 5-min illumination with white light. Pseudocolor difference image (scan in B − scan in A) highlights the drop in Ca²⁺ resulting from illumination (C) Scale bar in A is 10 μm. The blue end of the color scale represents a larger decrease in Ca²⁺; the red end of the scale represents a smaller decrease. To control for possible effects of scanning, control scans were taken before (D) and after (E) a continued period of 5 min in darkness. The difference image (scan in E − scan in D) shows no decrease in Ca²⁺ (F). Quantification of spatially averaged Ca²⁺ in cone terminals by two-photon imaging of fura-2. (G) The calibration curve was determined with a fura-2 calcium imaging calibration kit (Invitrogen) and fit with the standard equation (Grynkiewicz et al., 1985), yielding a best-fit K_d of 234 nM. For clarity, only the lower concentration portion of the sigmoidal calibration curve is shown (continuous line). (H) White light stimulation causes a 50% drop in internal Ca²⁺. Blocking rod and cone PDE with IBMX leads to a rise in Ca²⁺ above the dark level and eliminates the effect of light. Exposing the retina to Ca²⁺-free saline for 15 min causes Ca²⁺ to drop below the light level.