The Appearance, Distribution, and Longevity of Receptor-[¹²⁵I]T₃Complexes within the Nuclei of Isolated Rat Hepatocytes

Abstract

The nuclei of isolated rat hepatocytes were separable into three receptor compartments based upon their differential salt extractabilities: nucleoplasmic receptors (NP) extractable with 0.15 M KCl, high-salt extractable receptors (HSE) extractable with 0.4 M KCl, and salt-resistant receptors (SR) extractable with 0.4 M KCl/5 mM dithiothreitol. The receptor distribution among the three compartments was approximately NP, 45%; HSE, 30%; SR, 25%. The mean percent occupancy with endogenous T3 of the SR receptors (86%) was higher than the occupancies of the NP receptors (68%) and the HSE receptors (63%). When hepatocytes were pulsed with 3 nM [125I]T3 at 37 degrees C for brief intervals, receptor-[125I]T3 complexes were detectable in all three nuclear compartments within 15 sec. With increasing pulse intervals up to 120 sec, the receptor content of each nuclear compartment increased progressively and without evidence of preferential accumulation in any of the three compartments. To determine the life span and intercompartmental "migration" pattern of nuclear receptors, hepatocytes were pulsed with 3 nM [125I]T3 at 37 degrees C for 2.5 min or 5 min, followed by a chase with a 500-fold excess of nonlabeled T3. The population of receptor-[125I]T3 complexes generated during the pulse was serially recovered at increasing intervals after the chase. The complexes of each compartment dissociated with a half-life of approximately 3 min and manifested no predilection to accumulate in any of the compartments. Exposure of isolated hepatocytes to 3 nM T3 for 5 min or 10 min at 37 degrees C induced no change in the gross intercompartmental distribution of receptors compared to control hepatocytes incubated without T3.(ABSTRACT TRUNCATED AT 250 WORDS)