Aldosterone and nuclear volume cycling

The response of target cells to the steroid hormone aldosterone has been di vided into acute nongenomic (<10 min) and sustained genomic (>10 min) actio n. In the light of recent experiments this nomenclature does not hold anymo re and should be abandoned. By applying atomic force microscopy (AFM) we ob served in living endothelial cells that aldosterone induces cell volume inc rease in less than 10 minutes. The cell nucleus was identified as the swell ing site. Hormone-induced nuclear swelling can reach 15 to 28% of total cel l volume dissipating within 30 minutes. This phenomenon could have function al impact on flow resistance in small blood vessels. AFM-investigation of t he intracellular signal pathway in nuclear envelope of aldosterone-injected Xenopus laevis oocytes visualizes putative intracellular receptors (40 kD granules) bound to nuclear pores 2 minutes after hormone injection, with su bsequent macromolecule translocation into the nucleus. 15 minutes later mac romolecules (800 kD plugs) appear in the central channels of the nuclear po res. The plugs resemble ribonucleoproteins that carry the aldosterone-induc ed mRNA to the ribosomes. We postulate that steroid-induced nuclear swellin g is caused by a shift of receptors/transcription factors from cytoplasm in to nucleoplasm followed by gene transcription. Nuclear volume returns to no rmal when mRNA export through the nuclear pores is finished. Thus, steroid- induced net-movements of macromolecules between intracellular compartments initiate shifts in cell volume compensated by volume regulatory transporter s and ion channels in the plasma membrane. Copyright (C) 2000 S. Karger AG Basel.