Overexpressing the SPL S94D variant in CHO cells results in a loss of function. (A) CHO cells were transfected with HA-tagged RGS18 and either Myc-tagged normal (WT) SPL or the phosphomimetic SPL S94D variant. After loading with Fura-2, the cells were stimulated with thrombin and changes in the cytosolic Ca²⁺ concentration were recorded. (B) Summary of 3 experiments (mean ± SEM). (C) Western blot showing equal expression of WT and S94D.