FIGURE 3.

External Ca²⁺ is required for STX3 phosphorylation at T14 in both rod and cone photoreceptor terminals. (A) Representative confocal images through the OPL show that phosphorylation of STX3 at T14 in photoreceptors terminals in dark-adapted retinal eyecups (top panel) is abolished by the omission of Ca²⁺ from the external bath solution (“O Ca,” bottom panel). Scale bar = 5 μm. (B) In rod spherules, the pSTX3/STX3 ratio in dark-adapted retinal eyecups was greatly reduced in the absence of external Ca²⁺ (p < 0.0001) and indistinguishable from that of light-treated eyecups, with or without external Ca²⁺; p = 0.6035 and 0.6928, respectively. (C) In cone pedicles, the high pSTX3/STX3 ratio in dark-adapted eyecups was reduced in the absence of external Ca²⁺ to levels indistinguishable from that of light-treated eyecups, with or without external Ca²⁺; p = 0.3016; p = 0.998, respectively. For (B,C), n = 4,4 (mice). **indicates p < 0.01, ****Indicates p < 0.0001, and ^†indicates that p approaches significance.