Expression und Lokalisation der PMCA-Isoformen 1 bis 4 in den Geschlechtsorganen des Bullen und Interaktion des Enzyms mit dem Bläschendrüsenprotein PDC-109

The steep Ca2+-gradient between the intracellular and the extracellular space is maintained by effective Ca2+-transporting enzymes. One of these enzymes is the Plasma membrane Ca2+-ATPase (PMCA). The various PMCA isoforms and splice variants show developmental-, tissue-, and cell-specific patterns of expression. Studies on knockout mice carrying PMCA1, PMCA2 or PMCA4 null mutations point out to the in vivo function of the different isoforms. Atp2b1-/- mice are embryonic lethal, Atp2b2-/- mice are ataxic and profoundly deaf. Homozygous mice with a targeted gene deletion of PMCA4 are infertile due to severely impaired sperm motility. Null mice show normal spermatogenesis and mating behaviour, but sperm of these animals can not achieve a hyperactivated state of motility. Furthermore, PMCA4 is essential for achieving a low resting Ca2+ concentration in mouse sperm. Therefore, a pivotal role of PMCA4 on the regulation of sperm function and intracellular Ca2+ levels in sperm was claimed. The study analyzes the gene and protein expression of PMCA4 in bull testis and epididymis, as this isoform is believed to be essential for sperm fertilization capacity. It focuses on the differential expression of the two isoforms PMCA4a and 4b and tries to elucidate a functional implication.