CALCIUM, CAMP, AND DOPAMINE AFFECT SINGLE MAMMOTROPHS ASSAYED BY HEMOLYTIC PLAQUES

We investigated the effects of dopamine, forskolin, and maitotoxin on prolactin release from individual rat and monkey mammotrophs. Forskolin increases cAMP levels, whereas maitotoxin amplifies the influx of extracellular calcium. Prolactin secretion from single mammotrophs was visualized by the reverse hemolytic plaque assay and then quantified by measuring the proportion of plaque-forming cells and the mean plaque area. In the presence of dopamine alone both the plaque proportion and mean area of the plaques formed by rat mammotrophs decreased by 50 and 40%, respectively. This inhibition of secretion was blocked by the dopaminergic antagonist spiperone as well as forskolin and maitotoxin. Forskolin and maitotoxin alone significantly elevated both the proportion (+30%) and area (+180% for forskolin and +250% for maitotoxin) of the plaques. These actions of maitotoxin were neutralized by D-600, a calcium channel blocker. All of these agents induced similar trends with monkey prolactin cells. We conclude that single mammotrophs in culture respond to perturbations in a differential manner and in a way predicted by earlier results based on macropopulation measurements.