IMAGING NUCLEAR-PORES OF ALDOSTERONE-SENSITIVE KIDNEY-CELLS BY ATOMIC-FORCE MICROSCOPY

In nuclei of renal target cells, aldosterone enhances transcriptional activity followed by the translocation of specific RNA molecules acros s the nuclear envelope. Trafficking between cell nucleus and cytoplasm occurs via nuclear pore complexes (NPCs) located in the double-layere d nuclear envelope. We investigated the nucleocytoplasmic transport ro ute by structure-function analysis at subcellular level in quiescent a nd aldosterone-stimulated cells. With atomic-force microscopy (AFM) we imaged individual pores of the nuclear surface of cultured kidney cel ls and related the number of pores per mu m(2) to nuclear envelope con ductance (G(n), per mu m(2)) evaluated electrically by current injecti on into the isolated nucleus. NPCs were equally distributed resembling ''donut-like'' structures with outer diameters of 134 +/- 12 nm (n = 50), each equipped with a central channel. Six hours of aldosterone ex posure (0.1 mu M) increased the number of NPCs per mu m(2) of nuclear surface from 7.4 +/- 0.4 to 9.8 +/- 0.4 (n = 12; P < 0.01). At the sam e time G(n) rose from 6900 +/- 520 to 9600 +/- 610 pS/mu m(2) parallel ed by an increase of the intranuclear electrical potential from -2.8 /- 0.2 to -6.2 +/- 0.4 mV (n = 18; P < 0.01). Assuming that NPCs repre sent the sole conductive pathway in the nuclear envelope, we calculate a mean single NPC conductance of 932 and 980 pS, in the absence and p resence of aldosterone, respectively. We conclude that aldosterone fac ilitates nucleocytoplasmic transport by increasing the number of NPCs but not by modifying their biophysical properties. Possibly, aldostero ne controls similar transport mechanisms in both plasma membrane and n uclear envelope.