Fig. 1.

Indicator dyes do not significantly influence the light response. a, Quantum bumps recorded in response to a 1.5 sec stimulus of identical intensity in a cell loaded with 100 μmINDO-1 are similar to those recorded from another cell with control intracellular solutions containing no Ca²⁺ buffers.b, Similarly, Fluo-3 (100 μm) has little or no effect on responses to 20 msec flash or 500 msec step of light (the difference in absolute amplitudes is well within the experimental variability). Thedotted trace shows the response to a second 500 msec stimulus recorded 2 min after making a Ca²⁺measurement using a submaximal 100 msec flash containing ∼10⁷ effective photons. All responses recorded in standard Ringer’s solution (1.5 mmCa²⁺) at a holding potential of −70 mV. Stimulus intensity in b was 3.8 × 10⁴effective photons · sec⁻¹ (calibrated from bump counts as in a).