Figure 4. Conditioning applications of extracellular [Ni²⁺] inactivate the cytosolic [Ca²⁺] response to subsequent [Ni²⁺] applications.

A, representative traces showing the effect of conditioning with extracellular [Ni²⁺] (0.5-3 mM) on the cytosolic [Ca²⁺] change induced by the subsequent application of 5 mM [Ni²⁺] (open bar) to cultured TM3 cells. The scale bar refers to changes in the levels of the cytosolic [Ca²⁺] (nM) in the bottom trace. B, effect of a range of conditioning extracellular [Ni²⁺] (0.5-5 mM) on the mean peak change (Δ) in cytosolic [Ca²⁺] (nM) elicited by the subsequent application of 5 mM [Ni²⁺]. The latter data points were derived by subtracting the basal from peak cytosolic [Ca²⁺]. Each data point was then compared with the response to a conditioning 0.5 mM [Ni²⁺] (regarded as control) by ANOVA with Bonferroni's correction for inequality. P values shown, n = 4–6 for each point.