Simulation of the interactions of Mn ²⁺ with a slow buffer (Pv). Traces show (from top to bottom): a, free [Ca²⁺]; b, Ca²⁺ bound to Pv; c, Mg²⁺ bound to Pv; d, free [Mg²⁺]; e, free Pv; f, free [Mn²⁺ ]; g, Mn²⁺ bound to Pv. A bolus of Ca²⁺ was added at 1 s. The solid black trace was obtained in the absence, and the red dashed in the presence of 20 nM free Mn²⁺. (See Eisner et al., 2023 for model). The equilibrium constants and therefore the associated rate constants for Mn²⁺ binding to the intracellular buffers, including Fura2, were estimated from the reported values relative to Ca²⁺Martell and Smith (1974), i.e., EGTA logK_Ca 11.0, logK_Mn = 12.3, logK_Mg = 5.28; EDTA: logK_Ca = 10.7, logK_Mn = 12.0, logK_Mg = 8.8.