Student Theses and Dissertations

Date of Award

1971

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Abstract

A new method was developed to measure magnesium transfer across the plasma membrane. This technique made use of the ligand, 8-hydroxyquinoline- 5-sulfonic acid (8-0H-Q) which fluoresces in the presence of magnesium and was used to demonstrate epinephrine stimulation of magnesium uptake.

The ligand was incorporated into plasma membrane vesicles prepared from rat epididymal fat cells. In the presence of calcium and magnesium but not in the presence of calcium alone, epinephrine and other lipolytic hormones stimulated an increase in fluorescence which was equivalent to an increase in intravesicular magnesium of 1.2 mM. The influx rate of magnesium entering the intravesicular space was calculated to be 10.2 micromoles of magnesium per gram of protein during the first thirty minutes. ACTH stimulation also caused an increase in fluorescence at a slower rate. Insulin and ouabain blocked the lipolytic hormone stimulated increase in fluorescence.

The uptake and retention of magnesium during epinephrine stimulation of plasma membrane vesicles was confirmed using radioactive magnesium (28Mg). Epinephrine stimulation of magnesium uptake in whole fat cells was shown using 2Mg and atomic absorption analysis of cold magnesium. Calcium potentiated the increase in magnesium retention following epinephrine stimulation.

Magnesium was shown to potentiate the decrease in fatty acid synthesis during epinephrine stimulation of fat cells. Uniformly labeled· l4C glucose was used for these studies.

These results are discussed in terms of a hypothetical model by which changes in intracellular magnesium concentration could account for changes in metabolism seen during lipolytic hormone stimulation of adipocytes.

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