Ascorbic acid transport by a clonal line of pheochromocytoma cells

A clonal line of rat pheochromocytoma cells was used as a model of noradrenergic tissue to study ascorbic acid transport. These cells were used because, like sympathetic neurons, they synthesize large amounts of noradrenaline in the presence of ascorbate, they respond to nerve growth factor with the production of neurites and they release, store and take up catecholamines. In these cells, both with and without nerve growth factor (NGF) treatment, [14C]ascorbic acid was concentrated by a stereospecific saturable, energy dependent transport system that could be described by a Michaelis-Menten transport model. The Kt and Vmax for ascorbic acid were approximately 0.03 mM and 0.3 nmole per min per mg protein respectively for both untreated and NGF-treated cells. The ability of the cells to concentrate ascorbic acid was not due to intracellular binding. Cells untreated with NGF and loaded with [14C]ascorbic acid to a concentration of 5.6 nmoles per mg protein retained only 6% of the initial intracellular [14C]ascorbic acid after the 24 h in normal growth medium. Thus, although pheochromocytoma cells contain an ascorbate concentrating system, optimal production of noradrenaline requires ascorbate in the medium.