Autoradiographic study of nuclear localization of aldosterone binding sites in intact renal cells: lack of temperature dependency

Abstract

We examined by autoradiography on intact target cells the nucleocytoplasmic distribution of aldosterone-receptor complexes and the thermodependency of the nuclear translocation process. Autoradiographs (dry films) were performed on cortical collecting tubules isolated by microdissection, after incubation of rabbit kidney pyramids with [3H]aldosterone (2 X 10(-9)M) in the presence or absence of an excess unlabelled aldosterone (X100). Paired experiments were done at 30 degrees C (1 h) or 4 degrees C (2 h). In both cases, the specific labelling was exclusively nuclear. Values were higher at 30 degrees C (14.5 +/- 1.5 specific silver grains per 100 micron2) than at 4 degrees C (5.4 +/- 0.6), with no concommitant cytoplasmic labelling (4 degrees C:0.7 +/- 0.3; 30 degrees C: -0.04 +/- 0.6). At 30 degrees C, addition of unlabelled spirolactone (X200) prevented the observed autoradiographic nuclear accumulation of aldosterone-receptor complexes, suggesting that cytoplasmic binding preceded the nuclear entry. The results suggest that, in intact cells, almost all aldosterone receptor complexes accumulate in nuclei, and that this process does not depend on temperature. In parallel biochemical-binding series we found the classical distribution of aldosterone receptor complexes both in cytoplasm and nuclei, and the classical thermodependency of nuclear translocation. The present autoradiographic results, together with similar observations reported for sex steroids (Martin P.M. and Sheridan P. J., J. steroid Biochem. 16 (1982) 215-229), question the classical model of thermodependent nuclear translocation, based on biochemical experiments.