LIPID SYNTHESIS AND SECRETION BY MAMMARY CELL ACINI AND CITRATE TRANSPORT BY BOVINE MAMMARY ENDOMEMBRANES
Abstract
The lactating mammary gland consists of a heterogeneous cell population which enables the synthesis and secretion of milk. Although mammary tissue contains a variety of cell types, only mammary epithelial cells are believed to be responsible for milk synthesis and secretion. These cells are arranged spherically to form an alveolus which is the individual secretory unit of the mammary gland. Isolated alveoli, acini, were used as models to monitor the effects of colchicine, vinblastine and cytochalasin B on lipid synthesis and secretion. The vinca alkaloid, colchicine, at a concentration of 1 mM was observed to slightly stimulate CO(,2) production and lipogenesis by acini. Lower concentrations of colchicine, 100 uM and 10 uM, were without effect on CO(,2) production and lipogenesis by acini. Colchicine inhibited acinar lipid secretion in a dose dependent manner. The lowest concentration of colchicine (10 uM) was without effect on acinar lipid secretion. Vinblastine, like colchicine, inhibited acinar lipid secretion in a dose dependent manner. Unlike colchicine, vinblastine also inhibited acinar lipid synthesis from ('3)H(,2)O and glucose. Cytochalasin B, a drug which disrupts microfilaments, inhibited acinar lipid synthesis and secretion. In addition, cytochalasin B, at concentrations of 50 uM and 5 uM, significantly inhibited CO(,2) production from glucose. Bovine and caprine milks contain 7 mM citrate. The mechanism responsible for citrate accumulation in milk was shown to be exocytosis. Bovine mammary acini were observed to be impermeable to citrate. Secretory vesicles were shown to be less capable of citrate transport than either Golgi apparatus or endoplasmic reticulum. The Golgi apparatus and endoplasmic reticulum proved equally competent in citrate uptake. Fluorocitrate and ATP were observed to inhibit citrate transport into Golgi apparatus and the mechanism of ATP inhibition appeared to be of the noncompetitive type.
Degree
Ph.D.
Subject Area
Anatomy & physiology|Animals
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