Calmodulin content of rat mammary tissue and isolated cells during pregnancy and lactation

Publisher Website
Google Scholar
Abstract
The calmodulin content of heat-treated extracts of rat mammary tissue and isolated cells was measured by using stimulation of cyclic nucleotide phosphodiesterase (PDE) activity and radioimmunoassay (RIA) procedures. The calmodulin content of mammary tissue increased 2.5-fold near the time of parturition, remained at the elevated level during lactation, then, after the onset of involution, decreased to values similar to those measured from mammary tissue of pregnant rats. When tissue from 15 animals in different stages of pregnancy, lactation and involution were compared, the RIA gave 2.6-fold higher results than the PDE assay. To investigate further the increase in calmodulin content of mammary tissue, secretory and myoepithelial cells were enzymically dissociated from rat mammary tissue during different stages of pregnancy, lactation and involution. Protein, DNA, lactose, G-6-P dehydrogenase and alkaline phosphatase were assayed to characterize the cell fractions. By using RIA, the calmodulin content per mg of protein in isolated secretory-cell fractions was high near parturition, then decreased and remained relatively constant during lactation. The amount of calmodulin expressed per mg of DNA in secretory cells did not show a marked change near parturition, suggesting a constant amount of calmodulin per cell. The calmodulin content of myoepithelial cells dissociated from mammary tissue and measured by using RIA was 6-fold lower than in secretory cells and remained relatively constant during the course of lactation. The changing lvels of calmodulin in rat mammary tissue during development may be related to proliferation and destruction of secretory epithelial cells, events that occur near parturition and involution, respectively.