Constitutive and basal secretion from the endocrine cell line, AtT-20

In an attempt to generate antibody-secreting endocrine cells, the mouse pituitary cell line AtT-20, which is ouabain sensitive and HAT resistant, was fused to the mouse plasmacytoma, 4TOO1, which is ouabain resistant and HAT sensitive. Clones were selected that survived several rounds of selec-tion in medium containing ouabain (2.5 mM) and HAT. The surviving clones differed from wild type cells in that they grew slowly and extended thin branching processes several cell bodies in length. Individual subclones were tested by immunofluorescence, after fixation and detergent permeabilization of cells, for the expression of the endogenous hormone expressed by AtT-20 cells, ACTH. Metabolically labeled clones were also tested by immunoprecipitation for expression of the antibody produced by the plasmacytoma, IgG2b, x. Of 33 subclones that were recovered, none expressed antibodies, 30 expressed ACTH, two were mixed, containing both ACTH expressing and nonexpressing ceils, and one appeared to be an ACTH nonexpressor. None of the subclones retained the ouabain resistance of the myeloma parent.