Fig. 1. Time course of Phen Green (1 µmol l^–1) fluorescence quenching induced by addition of copper chloride at three different concentrations to buffer containing dye-equilibrated hepatopancreatic mitochondria. Arrows show the points where copper chloride was added to a stable fluorescence signal produced in the absence of the metal. This graph is representative of multiple similar recordings under experimental conditions reported in this study. Copper influx was estimated by the initial rate of fluorescence quenching observed over the first 120 s of incubation following addition of the metal. The excitation wavelength was 490 nm and the emission of the dye was recorded at 520 nm. Addition of 1 mmol l^–1 EDTA restored the fluorescent signal by complexing Cu²⁺ in solution.