In mammals, four different genes encode four PMCA isoforms. PMCA1 and 4 are expressed ubiquitously; PMCA 2 and 3 are expressed prevalently in the central nervous systems. More than 30 variants are generated by mechanisms of alternative splicing. The pump variants generated by alternative splicing at the C-terminal region of the protein (site C) are of particular interest, since this site contains the calmodulin-binding site. This domain, in the absence of calmodulin, interacts with the protein and keeps the pump in an inactive state. Calmodulin displaces the binding with the intramolecular receptors, removing the inhibition. This type of splicing occurs in all isoforms and causes the inclusion of one (or two) additional exons, or portion of exons, leading to a truncated version of the pump, which displays a shorter regulatory domain as compared to the full length variant. The truncated version of the pump is named a, the full length variant is named b variant. The second site of alternative splicing is located closer to the 5’ end of the gene (site A) in the cytosolic portion that connects the second to the third transmembrane domain of the pump. This portion is considered to be the “transducer domain” of the pump, since it seems to be involved in the conformational changes occurring during the transport cycle. Depending on the isoform, splicing at site A introduces one or more exons. The situation of PMCA2 is particularly complicated: three different exons, respectively of 33, 60 and 42 base pairs (bp) can be alternative introduced. In the w variant all three exons are included and their inclusion is responsible for the targeting of the PMCA2 pump to the apical pole of the plasma membrane in polarized cells; in the z variant all three exons are excluded. The physiological meaning of the existence of such elevated number of isoforms is not clear: it must be related to the cell specific demands of Ca2+ homeostasis, i.e., different PMCA isoforms could be recruited to specific regions of the plasma membrane by forming differential complexes with partner proteins (Brini and Carafoli, 2009). Their activity could be also modulated by the interaction with different proteins such for example the 14-3-3 protein which has an inhibitory role on isoform 1,3 and 4 but not on isoform 2 of the PMCA (Rimessi et al., 2005; Linde et al., 2008). An unusual PMCA2 splicing isoform (w/a) is responsible for Ca2+ extrusion from the stereocilia of hair cells, the sensory system of the inner ear. Ca2+ enters stereocilia of hair cells through mechanoelectrical transduction (MET) channels opened by the deflection of the hair bundle, and is exported back to endolymph by splicing isoform w/a of the PMCA2 pump. Ablation or missense mutations of the pump cause deafness, as described for several mutations identified in mice. Two deafness-inducing missense mutations (V586M, and G293S) were also identified in human families (Schultz et al., 2005; Ficarella et al., 2007). Our work functionally characterized the w/a isoform by overexpressing it in model cells. At variance with the other PMCA2 variants, w/a isoform became activated only marginally when exposed to a Ca2+ pulse. Ca2+ measurements in cells overexpressing different PMCA2 splicing variants indicate that the combination of the products obtained by alternative splicing occurring at two different sites is responsible for different functional characteristics of the pumps, that may be related to the different responsiveness to the acidic phospholipids, that, together with calmodulin, are the main PMCA activators. We also characterized the effects of several deafness-inducing mutations on PMCA activity (Ficarella et al., 2007, Spiden et al., 2008). All of them essentially delayed the dissipation of Ca2+ transients induced by cell stimulation. The mutations impaired the longer term export of Ca2+ a defect that could influence the fraction of MET channels open at rest in hair cells. By increasing Ca2+ near the stereocilia tips the pump would augment the probability of MET channels block and increase the rate of adaptation. Conversely, reduced Ca2+ levels would reduce the rate of adaptation and increase open probability thus making the sensory hair cells less able to respond to subsequent sonorous stimuli.