Figure 7. Ca²⁺ Measurements in cnx, WT, and ninaA.

(A) Ca²⁺ indicator measurements in cnx, wt, and ninaA^P269 photoreceptors loaded with the low-affinity single-wavelength indicator dye Fluo-4FF (100 µM) via the patch pipette and illuminated for 2 s with the same intensity 485 nm light (equivalent to ~10⁸ effectively absorbed photons/s in wt flies). Traces show the mean from n = 15cnx (cnx¹ and cnx² pooled), 10 wt, and 7 ninaA cells. For clarity, the error range(±SEM) is shown only for cnx. (B) In a ninaA^P269 cell, a second much brighter stimulus (7.5-fold higher intensity) induced only a slightly greater Ca²⁺ rise, excluding the possibility that the slightly greater quantum catch in cnx mutants (Figure S2) could underlie the greatly increased Ca²⁺ signal in the cnx mutants (n = 3). (C) SERCA and (D) CalX were expressed normally in the cnx mutants. (1) Wild-type (bw;st), (2) cnx¹, (3) cnx². Flies assayed in all of the lanes were 1–2 days old. The nitrocellulose membranes were stained with 0.05% Ponceau S to ensure that each lane contained the appropriate amount of protein. The same blot was reprobed with anti-tubulin antibody. Five heads were loaded per lane.