Ca-pumping by PMCA-neuroplastin complexes operates in the kiloHertz-range.

Ca-ATPases in the plasma membrane extrude Ca ions from the cytosol to the extracellular space thereby terminating Ca-signals and controlling Ca-homeostasis in any type of cell. Recently, these Ca-pumps have been identified as protein complexes of the transporting subunits PMCAs1-4 and the single-span membrane proteins Neuroplastin (NPTN) or Basigin that are obligatory for efficient trafficking of the pump complexes to the surface membrane. Quantitative investigation of the pumping velocity controlling the time course of Ca-signals, however, has remained unresolved. Here we show, using Ca-activated K channels as fast native reporters of intracellular Ca concentration(s) together with membrane-tethered fluorescent Ca-indicators, that under cellular conditions PMCA2-NPTN complexes can clear Ca in the low millisecond-range. Computational modeling exploiting EM-derived densities of Ca-source(s) and Ca-transporters in freeze-fracture replicas translated these fast kinetics into transport rates for individual PMCA2-NPTN pumps of more than 5000 cycles/s. Direct comparison with the Na/Ca-exchanger NCX2, an alternate-access transporter with established cycling rates in the kHz range, indicated similar efficiencies in Ca-transport. Our results establish PMCA2-NPTN complexes, the most abundant Ca-clearing tool in the mammalian brain, as transporters with unanticipated high cycling rates and demonstrate that under cellular conditions ATPases may operate in the kHz-range.