Figure 1.

4-CEP induced Ca²⁺ release but abolished store-operated Ca²⁺ entry in rat L6 myoblasts and HEK293 cells co-expressing STIM1/ORAI1. (A) Structures for 4-CEP, 4-CmC, 4-ClP and caffeine. (B) The effects of 4-CEP, 4-CmC and 4-ClP on the cytosolic Ca²⁺ level in rat L6 myoblasts. The cells were maintained in Ca²⁺ free solution first and then perfused with different compounds (500 μM for each compound) in Ca²⁺ free and 1.5 mM Ca²⁺ solution as indicated by the arrows. (C) 4-CEP (500 μM) nearly abolished the TG (1 μM)-induced Ca²⁺ influx in the myoblasts. (D) Mean ± SEM data for the comparison of Ca²⁺ release and influx induced by 4-ClP, 4-CmC, 4-CEP and TG in the myoblasts (n = 19–40 cells in each group). (E) The effects of 4-CEP, 4-CmC and 4-ClP (500 μM) in STIM1/ORAI1 cells. (F) 4-CEP (500 μM) abolished the TG (1 μM)-induced Ca²⁺ influx in STIM1/ORAI1 cells. (G) Mean ± SEM data for Ca²⁺ release and influx induced by 4-ClP, 4-CmC, 4-CEP and TG in the STIM1/ORAI1 cells (n = 18–26 cells in each group). Ca²⁺ release was measured as the peak of Ca²⁺ release signal; and Ca²⁺ influx was measured at 1 min after Ca²⁺ re-addition. One-way ANOVA with Bonferroni test was used for (D) and (G). ** P < 0.01, *** P < 0.001.