Active transport of triiodothyronine (T 3) into isolated rat liver cells

Abstract

Since the receptors for thyroid hormones are located within the cell [I] , these hormones have to be transported from the extracellular compartment through the plasma membrane into the cell. Only scarce and conflicting data concerning this transport mechanism are available. Both diffusion [2-4] and carrier-mediated processes [ 5-71 have been described or suggested. In view of the fact that amino acids [S] are transported through the plasma membrane by active or mediated processes, it is not likely that thyroid hormones enter the cell by diffusion only. In an attempt to gain more insight into the mechanism of cellular uptake of T3 the present study was performed. As a model we have chosen non-proliferative cultures of parenchymal cells from adult rat liver. The use of primary cultures offers a distinct advantage over freshly prepared liver cell suspensions. Cells are given time to recover from the damage associated with the isolation, such as temporary changes in the inability to concentrate amino acids [9] and the increased catabolic state during the first 24 h after isolation [lo] . In this report, we describe the basic characteristics of T3 uptake in this system. A preliminary account of this work has been publi~ed [l I].