title: Angiotensin II increases the cytosolic calcium activity in rat podocytes in culture.
abstract: In the glomerulus, angiotensin II (Ang II) reduces the ultrafiltration coefficient and enhances the filtration of macromolecules. During glomerular injury, inhibition of the renin-angiotensin system by angiotensin-converting-enzyme inhibitors reduces proteinuria and retards the progression to end-stage renal insufficiency. The mechanisms by which Ang II modulates glomerular function are still a matter of investigation. To study whether Ang II may regulate the cytosolic calcium activity ([Ca2+]i) in podocytes, these cells were propagated in short-term culture and the effect of Ang II was examined with the Fura-2 microfluorescence technique in single podocytes. The cellular identity of cultured podocytes was proven by the expression of WT-1 and pp44, specific antibodies against podocytes in vivo. Ang II led to a concentration-dependent, reversible and slow increase of [Ca2+]i with an EC50 of 3 nmol/liter Ang II (N = 229). Ten nmol/liter Ang II increased [Ca2+]i from 41 +/- 9 to 260 +/- 34 nmol/liter (N = 210). In a solution with an extracellular reduced Ca2+ concentration of 10 micromol/liter, Ang II-mediated [Ca2+]i increase was significantly reduced by 60 +/- 20% (N = 12), indicating that the [Ca2+]i increase was due to a Ca2+ influx from the extracellular space and a release of Ca2+ from intracellular stores. Flufenamate, an inhibitor of non-selective ion channels, significantly inhibited Ang II-mediated increase of [Ca2+]i (IC50 = 20 micromol/liter, N = 29), whereas the L-type Ca2+ channel blocker nicardipine even in high concentrations of > 1 micromol/liter had only a small inhibitory effect. The AT1 receptor antagonist losartan inhibited Ang II-mediated [Ca2+]i increase with an IC50 of about 0.3 nmol/liter (N = 35). The data suggest that Ang II increases [Ca2+]i in podocytes by an influx of Ca2+ through non-selective channels and by a release of Ca2+ from intracellular stores. The effect of Ang II is mediated via an AT1 receptor.
authors.affiliation: Department of Medicine, Albert-Ludwigs-Universität Freiburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Henger
authors.forename: T
authors.initials: T
authors.lastname: Huber
authors.forename: K G
authors.initials: KG
authors.lastname: Fischer
authors.forename: R
authors.initials: R
authors.lastname: Nitschke
authors.forename: P
authors.initials: P
authors.lastname: Mundel
authors.forename: P
authors.initials: P
authors.lastname: Schollmeyer
authors.forename: R
authors.initials: R
authors.lastname: Greger
authors.forename: H
authors.initials: H
authors.lastname: Pavenstädt
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D005439:Flufenamic Acid / Q000494:pharmacology; D007678:Kidney Glomerulus / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D009529:Nicardipine / Q000494:pharmacology; D009994:Osmolar Concentration; D051381:Rats; D011945:Receptors, Angiotensin / Q000502:physiology
chemical_list: D011945:Receptors, Angiotensin; D000804:Angiotensin II; D005439:Flufenamic Acid; D009529:Nicardipine; D002118:Calcium