Submitted to: Federation of American Societies for Experimental Biology Conference
Publication Type: Abstract Only
Publication Acceptance Date: April 19, 1998
Publication Date: N/A
Technical Abstract: The transcellular Ca2+ fluxes required for milk production must be rigorously regulated to maintain the low cytosolic Ca2+ concentrations critical to cell function. Ca2+-ATPase's play a critical role in the maintenance of cellular calcium homeostasis. In specialized tissue (e.g. mammary gland), unique patterns of Ca2+-ATPase expression and isotypes may be expected to compensate for the large calcium load of lactation. Using RT-PCR and sequencing, we identified 6 calcium pumps in lactating mammary tissue. Three plasma membrane Ca2+-ATPase's were found (PMCA1b, 2b, 4b). Two sacoplasmic/endoplasmic reticulum Ca2+-ATPase's were identified (SERCA2 and 3) and the rat homologue to the yeast golgi Ca2+-ATPase was found (RS-10). The patterns of mRNA expression of each of these pumps was examined in rat mammary tissue from rats 7-d pregnant to 21-d lactating. Northern blots revealed increased mRNA expression for all calcium 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 3-8 times more abundant than SERCA and PMCA1b and 4b. RS-10 was the only pump to increase near parturition. PMCA2b was the most abundant transcript found in lactating mammary tissue. At peak lactation, PMCA2b's expression approached that of actin. PMCA2b's high expression, high affinity for calcium, and high activity at low calmodulin concentrations suggest that PMCA2b is uniquely suited for maintenance of calcium homeostasis in the lactating mammary gland. RS-10's pattern of expression and abundance suggests that RS-10 is a candidate for the golgi Ca2+-ATPase shown to be important in maintaining golgi CA2+ concentration required for casein synthesis and micelle formation.