Plasma membrane Ca²⁺-ATPases can shape the pattern of Ca²⁺ transients induced by store-operated Ca²⁺ entry

Calcium (Ca²⁺) is a critical cofactor and signaling mediator in cells, and the concentration of cytosolic Ca²⁺ is regulated by multiple proteins, including the plasma membrane Ca²⁺-ATPases (adenosine triphosphatases) (PMCAs), which use ATP to transport Ca²⁺ out of cells. PMCA isoforms exhibit different kinetic and regulatory properties; thus, the presence and relative abundance of individual isoforms may help shape Ca²⁺ transients and cellular responses. We studied the effects of three PMCA isoforms (PMCA4a, PMCA4b, and PMCA2b) on Ca²⁺ transients elicited by conditions that trigger store-operated Ca²⁺ entry (SOCE) and that blocked Ca²⁺ uptake into the endoplasmic reticulum in HeLa cells, human embryonic kidney (HEK) 293 cells, or primary endothelial cell isolated from human umbilical cord veins (HUVECs). The slowly activating PMCA4b isoform produced long-lasting Ca²⁺ oscillations in response to SOCE. The fast-activating isoforms PMCA2b and PMCA4a produced different effects. PMCA2b resulted in rapid and highly PMCA abundance-sensitive clearance of SOCE-mediated Ca²⁺ transients, whereas PMCA4a reduced cytosolic Ca²⁺, resulting in the establishment of a higher than baseline cytosolic Ca²⁺ concentration. Mathematical modeling showed that slow activation was critical to the sustained oscillation induced by the "slow" PMCA4b pump. The modeling and experimental results indicated that the distinct properties of PMCA isoforms differentially regulate the pattern of SOCE-mediated Ca²⁺ transients, which would thus affect the activation of downstream signaling pathways.