sentences:  Another, more ubiquitous transmembrane pump that exports calcium from the cell is the plasma membrane Ca2+ ATPase (PMCA), which has a much higher affinity but a much lower capacity.Since the PMCA is capable of effectively binding to Ca2+ even when its concentrations are quite low, it is better suited to the task of maintaining the very low concentrations of calcium that are normally within a cell.The Na+/Ca2+ exchanger complements the high affinity, low capacitance Ca2+-ATPase and together, they are involved in a variety of cellular functions including