Figure 4. Effect of thimerosal on IICR in the presence or absence of 1 μM free Ca²⁺ in permeabilized A7r5 cells.

Data are plotted as fractional loss (the amount of ⁴⁵Ca²⁺ leaving the stores in 2 min divided by the total store Ca²⁺ content at that time) as a function of time in (A, B). (A) Effect of the presence (•) or absence (○) of 1 μM thimerosal on Ca²⁺ release provoked by 200 nM IP₃ in the absence of Ca²⁺. (B) Effect of the presence (•) or absence (○) of 1 μM thimerosal on Ca²⁺ release provoked by 200 nM IP₃ in the presence of 1 μM free Ca²⁺. (C) Bell-shaped dependence of the effect of thimerosal on IICR. Data are plotted as the difference between the fractional loss after the addition of IP₃ and the fractional loss before the addition of IP₃ as a function of the thimerosal concentration: ○, 200 nM IP₃, 1 mM EGTA; □, 200 nM IP₃, 1 μM free Ca²⁺; Δ, 750 nM IP₃, 1 mM EGTA. (D) Effect of NEM (○), diamide (□) and SIN-1 (Δ) on IICR. Data are plotted as the difference between the fractional loss after the addition of IP₃ and the fractional loss before the addition of IP₃ as a function of the NEM, diamide or SIN-1 concentration respectively. The experiment was performed using 750 nM IP₃ and in the presence of 1 mM EGTA. Each curve represents the means±S.E.M for three wells.