The specific objectives of the work proposed are to determine the mechanisms by which calcium is transported across plasma and vesicular membranes of the mammary cell and to determine the role of calcium in the control of mammary function. We will use short-term, in vitro studies of mammary glands from pregnant and lactating mice to determine the role of sodium-calcium exchange across the basolateral membranes of the cell in maintaining the cytosolic level of calcium. Similar experimental materials will be used to study the role of calcium in regulating lactogenesis. Membrane vesicles isolated from the mammary glands of pregnant and lactating mice will be characterized and investigated for Ca ATPase activity and for ATP-dependent calcium transport. The distribution of this activity in membrane vesicular fractions of the mammary alveolar cell will be determined. The role of the apical membrane in calcium transport will be assessed in studies on the milk fat globule membrane from bovine milk. Finally, cultures of mammary cells from pregnant and lactating mice will be grown on floating collagen membranes in the presence of suitable hormones using methods developed in the laboratory of D. Pitelka. The resulting epithelial pavement will be characterized for its suitability as a two-dimensional model system for the study of the regulation of calcium transport in a secretory epithelium. Eventually we hope to use this model culture system for studies of the cellular mechanisms of hormonal control of differentiation and exocrine secretion in the mammary gland.