Fura-FF pentapotassium salt is a fura-2 derivative that has Ca²⁺ sensitivity similar to mag-fura-2, but is relatively insensitive to Mg²⁺. This water-soluble salt form is useful for intracellular loading by microinjection, infusion from patch pipette or uptake induced by our Influx pinocytic cell-loading reagent (I-14402).