Using FluoZin-3 and fura-2 to monitor acute accumulation of free intracellular Cd(2+) in a pancreatic beta cell line

The understanding of cellular Cd(2+) accumulation and toxicity is hampered by a lack of fluorescent indicators selective for intracellular free Cd(2+) ([Cd(2+)](i)). In this study, we used depolarized MIN6 mouse pancreatic beta cells as a model for evaluating [Cd(2+)](i) detection with commercially available fluorescent probes, most of which have been traditionally used to visualize [Ca(2+)](i) and [Zn(2+)](i). We trialed a panel of 12 probes including fura-2, FluoZin-3, Leadmium Green, Rhod-5N, indo-1, Fluo-5N, and others. We found that the [Zn(2+)](i) probe FluoZin-3 and the traditional [Ca(2+)](i) probe fura-2 responded most consistently and robustly to [Cd(2+)](i) accumulation mediated by voltage-gated calcium channels. While selective detection of [Cd(2+)](i) by fura-2 required the omission of Ca(2+) from extracellular buffers, FluoZin-3 responded to [Cd(2+)](i) similarly in the presence or absence of extracellular Ca(2+). Furthermore, we showed that FluoZin-3 and fura-2 can be used together for simultaneous monitoring of [Ca(2+)](i) and [Cd(2+)](i) in the same cells. None of the other fluorophores tested were effective [Cd(2+)](i) detectors in this model.