Minimal photobleaching of mbYFPQS occurs with repeated photo-stimulation.

<p>A. A cultured midbrain neuron expressing mbYFPQS was imaged with an exposure of 100 ms every 5 s for 35 min with less than 6% decrease in baseline fluorescence. B. A neuron imaged with the same parameters (100 ms exposure, every 5 s) that was whole-cell patch-clamped with potassium gluconate internal solution (12.6 mM Cl⁻). A decrease in fluorescence was observed with break-in to whole-cell mode (denoted by dotted line) but after reaching a new stable baseline, there was less than 5% decrease in fluorescence over 35 min of imaging. C. Brightfield and epifluorescence image of cell imaged in <i>B</i>. D. Bar graph of % increase in fluorescence of typical internal solutions (CsCl (134 mM Cl⁻); KGluconate (121 mM Gluconate/12.6 mM Cl⁻); KMeSO4 (121 MeSO4/12.6 mM Cl⁻)) compared to fluorescence in high intracellular chloride concentrations (158 mM Cl⁻). Experiments were done in perforated mbYFPQS-expressing neurons after incubation in ionophores used for chloride and pH calibration experiments. The results show that gluconate and methylsulfate ions do not appreciably quench the mbYFPQS fluorescence.