THE SIGNIFICANCE OF THE ISOFORMS OF PLASMA-MEMBRANE CALCIUM-ATPASE

The plasma membrane calcium ATPase (PMCA) or Ca2+ pump transports Ca2 ions out of the cells, by using the energy stored in ATP. It is essen tial in the control of Ca2+ concentration in the cytosol. The plasma m embrane Ca2+ pump has been found in all mammalian cells and is encoded by four independent genes. The number of possible isoforms is further increased by alternative splicing at two independent sites; transcrip ts for more than 20 isoforms have been detected. The PMCA isoforms, in particular some of their alternatively spliced isoforms, have been sh own to bind calmodulin with different affinity. The activity of these alternatively spliced pumps is possibly differently regulated by kinas e-mediated phosphorylation. A short summary of recent work on the prop erties of the PMCA isoforms is presented here.