Expression of bovine mammary gland Ca2+ATPases

Control of transcellular Ca2+ fluxes associated with lactation are critical to mammary function and Ca2+ homeostasis. Mammary Ca2+ transport and storage may contribute to the pathological hypocalcemia seen in dairy cows at parturition. RT-PCR and Western Blotting were used to identify which Ca2+ ATPases are present in the bovine mammary gland and in milk fat globule membranes (MFGM). PMCA1, PMCA2 and PMCA4 are plasma membrane Ca2+ ATPases expressed in the bovine mammary gland. A putative Golgi Ca2+ ATPase (bSPCA) is also found in significant amounts in the mammary gland. The expression of Ca2+ ATPases in the bovine mammary gland is associated with mammary gland development and lactation. The timing, magnitude and types of Ca2+ ATPases expressed in mammary gland suggest an important role for these Ca2+ ATPases in mammary and cow calcium homeostasis. The significant expression of PMCA2 postpartum and its unique biochemical activity imply an important role for PMCA2 in maintaining mammary gland Ca 2+ homeostasis during lactation. The expression of Ca2+ ATPases prepartum may also be associated with the development of hypocalcemia in the cow. The most striking finding is that the prepartal expression of bSPCA was correlated with the amount of calcium secreted into the first milk as well as the degree of hypocalcemia seen in cows. The cDNA of bSPCA was cloned and sequenced. The full-length cDNA of bSPCA has been submitted to;GENBANK (ACCESSION NO. AF230532). To understand the physiological functions of these Ca2+ ATPases on transcellular Ca2+ movement in lactating mammary secretory cells, the cellular locations of SPCA and PMCAs (apical vs. basolateral) was also established. Localizations of these Ca2+ ATPases by immunohistochemistry showed that SPCA is located in mammary secretory cells in the cytoplasm between the nucleus and the apical membrane, an area associated with the location of the Golgi. The PMCAs are located in both apical and basolateral membranes of secretory cells. PMCA2 and PMCA4 are located in the apical membrane of lactating cells. The apical location of PMCA2 and PMCA4 indicates that these PMCAs transport intracellular Ca2+ into milk