Ammonium Ion Effects on Hybridoma Cell Physiology

Citation

McQueen, Anne T. (1989) Ammonium Ion Effects on Hybridoma Cell Physiology. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/a159-dy39. https://resolver.caltech.edu/CaltechETD:etd-02122007-131458

Abstract

Ammonium ion is an important inhibitor of mammalian cell growth. Measurements of changes in hybridoma intracellular pH upon NH₄Cl addition (using a flow cytometric assay in which cells are stained with a pH-sensitive fluorescent dye) indicate that NH⁺₄ causes a steady-state cytoplasmic acidification. There is a correlation between NH₄Cl effects on growth and on intracellular pH, and these effects are independent of the external pH value, suggesting that NH⁺₄, not NH₃ (produced by the dissociation of NH⁺₄ at higher external pH values), is the species responsible for growth inhibition.

Ammonium ion has similar effects on batch growth in flasks in an incubator and in a bioreactor at controlled pH and dissolved oxygen concentration. Both decreases in the external pH value and increases in the NH₄Cl concentration inhibit glucose consumption in batch growth. This is hypothesized to be due to intracellular pH decreases. However, cell growth is not dependent on glucose consumption. Changes in the external pH value and in the NH₄Cl concentration, which result in growth inhibition, have no effect on the specific antibody production rate.

A mechanism is proposed and a mathematical model is developed to explain the intracellular pH decreases caused by NH⁺₄. This model incorporates a detailed description of the behavior of the Na⁺/H⁺-exchanger, which is assumed to be the main pH_i controller of the cell. The model is able to reproduce the salient features of the experimental results.

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