Modulation of aldosterone-induced stimulation of ENaC synthesis by changing the rate of apical Na+ entry.
Primary cultures of immunodissected rabbit connecting tubule and cortical collecting duct cells were used to investigate the effect of apical Na+ entry rate on aldosterone-induced transepithelial Na+ transport, which was measured as benzamil-sensitive short-circuit current (I(sc)). Stimulation of the apical Na+ entry, by long-term short-circuiting of the monolayers, suppressed the aldosterone-stimulated benzamil-sensitive I(sc) from 320 +/- 49 to 117 +/- 14%, whereas in the presence of benzamil this inhibitory effect was not observed (335 +/- 74%). Immunoprecipitation of [(35)S]methionine-labeled beta-rabbit epithelial Na+ channel (rbENaC) revealed that the effects of modulation of apical Na+ entry on transepithelial Na+ transport are exactly mirrored by beta-rbENaC protein levels, because short-circuiting the monolayers decreased aldosterone-induced beta-rbENaC protein synthesis from 310 +/- 51 to 56 +/- 17%. Exposure to benzamil doubled the beta-rbENaC protein level to 281 +/- 68% in control cells but had no significant effect on aldosterone-stimulated beta-rbENaC levels (282 +/- 68%). In conclusion, stimulation of apical Na+ entry suppresses the aldosterone-induced increase in transepithelial Na+ transport. This negative-feedback inhibition is reflected in a decrease in beta-rbENaC synthesis or in an increase in beta-rbENaC degradation.
Dijkink
L
L
Department of Cell Physiology, University Medical Centre Nijmegen, 6500 HB Nijmegen, The Netherlands.
Hartog
A
A
Van Os
C H
CH
Bindels
R J
RJ
D000450:Aldosterone / Q000494:pharmacology*; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D016764:Cell Polarity / Q000502:physiology; D002478:Cells, Cultured; D053503:Epithelial Sodium Channels; D005110:Extracellular Space / Q000378:metabolism; D005246:Feedback / Q000502:physiology; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000096:biosynthesis*; D013462:Sulfur Radioisotopes
D053503:Epithelial Sodium Channels; D015222:Sodium Channels; D013462:Sulfur Radioisotopes; C013407:benzamil; D000450:Aldosterone; D000584:Amiloride; D012964:Sodium