|Reinhardt, Timothy - Tim|
Submitted to: Federation of American Societies for Experimental Biology Conference
Publication Type: Abstract Only
Publication Acceptance Date: 4/19/1999
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Transcellular Ca2+ fluxes required for milk production must be rigorously regulated to maintain the low cytosolic Ca2+ concentrations critical to cell function. Ca2+-ATPases play a critical role in the maintenance of cellular Ca homeostasis. In the mammary gland, unique patterns of Ca2+-ATP xpression and isotypes may be expected to compensate for the large Ca load of lactation. Using RT-PCR and sequencing, we identified 6 different Ca pumps in lactating mammary tissue and examined their expression by Northern blotting. We examined the expression of the plasma membrane Ca2+-ATPases (PMCA1b, 2b, 4b) and the putative Golgi secretory pathway Ca2+-ATPases (SPCA) by Western blotting. Using an antibody that recognizes all PMCA isoforms (5F10), we found small amounts of PMCA protein in the mammary gland prior to parturition. As lactation started we found dramatic increases in PMCA protein expression. The use of isoform specific antibodies showed the increased PMCA protein expressed in lactating mammary tissue was primary PMCA2b. Relatively small amounts of PMCA1b and 4b protein were found in lactating tissue. PMCA4b appeared to be the major PMCA expressed in mammary tissue during gestation. SPCA protein expression in the mammary gland started to increase approx. 1 wk prior to parturition and continued to increase as lactation proceeded. PMCA2b's high expression, high affinity for Ca, and high activity at low calmodulin concentrations 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 that RS-10 is a candidate for the Golgi Ca2+-ATPases shown to be important in maintaining Golgi Ca2+ concentration required for casein synthesis and micelle formation.