Expression of A and B Types of Monoamine Oxidase in Differentiated Neuroblastoma Hybrid Cells

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Abstract
The total activities of monoamine oxidase (MAO) and the ratio of type B/type A activities were determined in mouse neuroblastoma N1E‐115 cells, and in NX31T and NG108‐15 hybrid cells derived from mouse neuroblastoma × rat sympathetic ganglion hybrid or mouse neuroblastoma × rat glioma hybrid cells. N1E‐115 and NX31T cells possessed type A activities exclusively, although NG108‐15 cells showed both type A (65–90%) and type B (10–35%) MAO activities. The activity of type A MAO in NX31T and N1E‐115 cells was relatively constant during culturing periods in the presence or absence of dibutyryl cyclic AMP (Bt2cAMP), whereas total MAO activity and the ratio of type B MAO/type A MAO in NG108‐15 cells increased as a function of culture periods. Prostaglandin E1 (PGE1) and theophylline, the best known combination to increase intracellular cyclic AMP content of NG108‐15 cells, caused similar increases of MAO and of the type B/type A ratio in NG108‐15 cells. The results suggest that MAO activity and expression of MAO B activity are regulated in NG108‐15 cells in a cyclic AMP‐dependent manner.