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 essential in the control of Ca2+ concentration in the cytosol. The plasma membrane 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; transcripts for more than 20 isoforms have been detected. The PMCA isoforms, in particular some of their alternatively spliced isoforms, have been shown to bind calmodulin with different affinity. The activity of these alternatively spliced pumps is possibly differently regulated by kinase-mediated phosphorylation. A short summary of recent work on the properties of the PMCA isoforms is presented here.