Submitted to: American Society for Bone and Mineral Research
Publication Type: Abstract Only
Publication Acceptance Date: December 1, 1998
Publication Date: N/A
Technical Abstract: The transcellular Ca**2+ fluxes required for milk production must be rigorously regulated to maintain the low cytosolic Ca**2+ concentrations critical to cell function. The many Ca**2+-ATPases in a cell play pivotal roles in maintaining intracellular Ca balance required for signal transduction and the functioning of numerous Ca dependent proteins. Using RT-PCR and sequencing, we identified 6 Ca pumps in lactating mammary tissue. Three plasma membrane Ca**2+-ATPases were found (PMCA-1b, 2b, 4b). Two sacoplasmic/endoplasmic reticulum Ca**2+-ATPases were identified (SERCA2 and 3) and the rat homologue to the yeast golgi Ca**2+-ATPase was found (RS-10). The patterns of mRNA expression of each of these pumps were examined in rat mammary tissue from rats 7 d pregnant to 21 d lactating. Northern blots revealed increased mRNA expression for all Ca pumps by d 7 of lactation and transcripts continued to increase through d 18 of lactation. PMCA1b and 4b and SERCA showed the lowest level of expression. RS-10 transcripts were 3-8x more abundant than SERCA and PMCA1b and 4b. RS-10 was the only pump transcript to increase prior to parturition. PMCA2b was the most abundant transcript found in lactating mammary tissue. At peak lactation PMCA2b's mRNA expression approached that of actin. PMCA2b's high expression, high affinity for Ca, and high activity at low calmodulin conc suggest that PMCA2b is uniquely suited for maintenance of Ca homeostasis in the lactating mammary gland. RS-10's pattern of expression and abundance suggest it is a candidate for the golgi Ca**2+-ATPase which is important in maintaining golgi Ca**2+ conc required for casein synthesis and micelle formation.