Figure 4. Inhibition of Ca-ATPase by thapsigargin. SR vesicles (0.1 mg/mL) from masseter (•), medial pterygoid (), and fast muscles () were incubated at 37°C in media containing 50 mmol/L MOPS-Tris (pH 7.2), 3 mmol/L ATP, 3 mmol/L MgCl₂, 100 mmol/L KCl, 0.1 mmol/L CaCl₂, 0.1 mmol/L EGTA, and thapsigargin as indicated in the abscissa. (A) Inhibition of Ca-ATPase activity. SR vesicles were incubated in the above medium with 10 µmol/L calcimycin added. The reactions and the Ca-ATPase activity determinations were performed as indicated in MATERIALS & METHODS. Bars, SD; n = 5. (B) Inhibition of ATP-dependent calcium uptake. SR vesicles were incubated in the above medium with the addition of tracer amounts of (⁴⁵Ca)CaCl₂. The reactions were performed as indicated in MATERIALS & METHODS. Bars, SD; n = 4.