Figure 4. Effect of FK506 on the uptake of exogenously added Ca²⁺ in permeabilized SH-SY5Y cells under oxalate-facilitated uptake conditions.

A, the effect of FK506 (50 μM) on Ca²⁺ uptake was measured by adding 4 pulses of exogenous Ca²⁺ (10 nmol) before and after FK506 application. The fluorescence signal is indicated in arbitrary units (A.U.), since it was difficult to estimate the [Ca²⁺] accurately in the presence of 20 mM oxalate. B, the 4 pulses before and after FK506 were normalized, averaged and superimposed. The mean decay (n= 4) of the [Ca²⁺] in control conditions and after addition of FK506 (50 μM) is plotted. This Ca²⁺ decay can be fitted by a monoexponential function (y= e^−t/τ), which resulted in a significant increase in the time constant τ of ≈35 % (P < 0.01 by Student's paired t test). Typical for 3 experiments. The inset shows the effect of the vehicle (0.1 % ethanol) on the uptake of exogenously added Ca²⁺ (average of 4 pulses of 10 nmol Ca²⁺). C, the effect of thapsigargin (4 nM or 1 μM) on the uptake of exogenously added Ca²⁺ (average of 4 pulses of 10 nmol Ca²⁺).