title: Aldosterone actions on basolateral Na+/H+ exchange in Madin-Darby canine kidney cells.
abstract: In recent studies, there has been a re-evaluation of the polarity of Na+/H+ exchange in Madin-Darby canine kidney (MDCK) cells. This study was designed to examine aldosterone actions on basolaterally located Na+/H+ exchange of MDCK cell monolayers grown on permeant filter supports; pHi was analysed in the absence of bicarbonate by using the pH-sensitive fluorescent probe 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein. Pre-exposure of MDCK cells to aldosterone led within 10-20 min to an alkalization of pHi (approximately 0.3 pH unit); this effect is prevented by an addition of dimethylamiloride to the basolateral superfusate. Addition of aldosterone led to stimulation of the basolaterally located Na+/H+ exchange activity (Na(+)-dependent recovery from an acid load); this effect required preincubation (more then 3 min) and was observed at 0.1 nM aldosterone. Pre-exposure (15 min) of MDCK monolayers to phorbol 12-myristate 13-acetate also led to an activation of Na+/H+ exchange; pre-exposure to 8-bromo-cAMP led to inhibition of Na+/H+ exchange activity. An inhibitory effect of aldosterone was observed if Na+/H+ exchange activity was analysed in the presence of aldosterone; the highest inhibitory effects (20%-30%) occurred at concentrations of 5 nM and higher. Aldosterone-dependent inhibition does not require preincubation and is fully reversible; it was only observed at low (20 mM) but not at high Na+ concentrations (130 mM). The data suggest that aldosterone has an instantaneous inhibitory effect on basolaterally located Na+/H+ exchange activity under conditions of low Na+, but stimulates the rate of transport activity upon preincubation under conditions of physiological Na+ concentrations.
authors.affiliation: Department of Physiology, University of Zürich, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Vilella
authors.forename: L
authors.initials: L
authors.lastname: Guerra
authors.forename: C
authors.initials: C
authors.lastname: Helmle-Kolb
authors.forename: H
authors.initials: H
authors.lastname: Murer
mesh_terms: D000450:Aldosterone / Q000494:pharmacology*; D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002460:Cell Line; D004285:Dogs; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D011493:Protein Kinase C / Q000494:pharmacology; D011494:Protein Kinases / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers
chemical_list: D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D000450:Aldosterone; D011494:Protein Kinases; D011493:Protein Kinase C