FIGURE 3.

A, comparison of Ca²⁺ transport activity measured on microsomal membranes isolated from CHO cells overexpressing PMCA2 z/b, w/b, and w/a variants. Membranes vesicles were preincubated at 37 °C, and Ca²⁺ uptake was initiated by the addition of 4 mm ATP (where indicated). 50 μm CaCl₂ was added where indicated. B, CaM dependence of Ca²⁺ uptake by microsomal membranes preincubated at 37 °C with 200 nm CaM. C, acidic phospholipid (PS) dependence of Ca²⁺ uptake by microsomal membranes preincubated at 37 °C with 25 μm PS. A–C, ATPase activity was indicated as the decrease of the absorbance at 340 nm. D, histograms show the means ± S.D. of the activity of the pumps. The activity was expressed as micromoles of P_i/min/μg of protein and calculated as indicated under “Experimental Procedures.” The data are representative of at least three experiments with different membranes preparations. *, p < 0.05, in respect to the respective controls in the absence of CaM and PS.