Figure 1. Depolarization with 35 mM extracellular K⁺ elicits sustained increases of [Ca²⁺]_in of photoreceptor cells.

Cells were treated using Protocol I, as described in Methods. Briefly, following preincubation with Fura-2AM, cells were washed and incubated in 2 ml of BSS. After obtaining 3.5 min (A) or 7 min (B) of baseline data, 0.667 ml of modified BSS containing 129.2 KCl and no NaCl was added to bring the final extracellular K⁺ concentration to 35 mM. The cells were allowed to remain in this medium for the remainder of the experiment. Fluorescence emission ratios were obtained at 1 min intervals throughout the experiment.

Figure 1A.

Line tracings of [Ca²⁺]_in of six cells in a single microscope field before and for 28 min during depolarization. Pseudocolor animation of the changes in [Ca²⁺]_in can be viewed in Figure 2; the data in the lower left corner of each frame correspond to the emission ratio number and the recording time. All five photoreceptor cells showed sustained increases of [Ca²⁺]_in, while the apparently undifferentiated round cell did not.

Figure 1B.

Pseudocolor montage of [Ca²⁺]_in of two photoreceptors exposed to depolarizing conditions for > 2 h. Panel I: 5 min before exposure to 35 mM K⁺; panels II, III, and IV: 4 min, 1 h, and 2 h, respectively, following addition of KCl. Both cells showed sustained increases of [Ca²⁺]_in, but the magnitude of the response differed greatly between them.

Figure 1C.

A phase-contrast image of the cells analyzed in B, photographed under dim visible light and 380 nM illumination, is shown with the outline for integration of the fluorescence emission-ratio signal.