Figure 8. Magnitude of Ca²⁺ release as a function of the duration of prior light exposure in Ringer solution.

Protocol as for Fig. 6A and B but duration of light exposure was varied. A, ratio of fluo-5F fluorescence evoked by first laser pulse (P1) divided by mean pedestal response. Each histogram column gives mean ±s.e.m.; n= 11. First histogram column is for paired controls for which no light exposure was given (as in Fig. 6A), and following three columns are for 4, 9 and 29 s exposure in Ringer solution to a saturating light of intensity of 1.37 × 10³ photons μm⁻² s⁻¹. Since the outer segment was stepped into 0 Ca²⁺, 0 Na⁺ solution 1 s before the end of illumination, the total durations of illumination were 5, 10 and 30 s respectively. Even the 30 s exposure produced a bleach of less than 0.03 % of the visual pigment. B, mean ±s.e.m. for the difference in the fluo-5F fluorescence evoked by the first and second laser pulses (P2 - P1) divided by the mean value of the pedestal. Data from the same experiments as in An = 11. Bleaches were calculated as described in the Methods for the total duration of each light exposure (i.e. for 5, 10 and 30 s exposures). C, data from B replotted as a function of the duration of the light exposure in Ringer solution. Data have been fitted with a single exponential curve of time constant of 4.0 ± 0.3 s using a weighted least-squares algorithm.