Figure 4. Extracellular Ca2+ is required for hyperpolarization-induced Sp4 degradation.
(A) Western analysis of Sp4 after incubation of CGNs for 60 min in control or EGTA-treated culture medium. Sp1 and c-Fos were used as negative and positive controls, respectively. (B) Graph shows mean (n = 6) Sp4/GAPDH ratio (±SEM) of cells treated as in (A). A two-way ANOVA indicates a main significant effect of KCl [F1,20 = 11.12, p < 0.005] and EGTA [F1,20) = 8.06, p < 0.05]. The interaction effect between the two factors is significant, F1,20 = 8.23, p < 0.01. Graphical representation shows that EGTA affects Sp4 protein abundance only when the extracellular concentration of KCl is 5mM. Post hoc comparisons between two means were conducted using the Bonferroni correction, **p < 0.01; ***p < 0.001.