Electroporation has become a useful tool for the introduction of biomolecules to a variety of cell types since the method was first described (1,2). This technique has also been used for important functional studies in the different GH cell strains: rat pituitary tumor cells that produce prolactin or growth hormone. In most cases, transient-expression experiments have been used to study cellular processes, such as rat growth hormone gene expression (3), prolactin promotor activity (4–7), and the transcription regulatory properties of hormones, such as thyroid hormones and retinoic acid (8–12).